UNIVERSITY OF ZIMBABWE · Relationship between stream bank cultivation and soil erosion in Dedza,...

UNIVERSITY OF ZIMBABWE

RELATIONSHIP BETWEEN STREAM BANK CULTIVATION AND SOIL

EROSION IN DEDZA, MALAWI

By

Chimango Mlowoka

A thesis submitted in partial fulfillment of the requirements of the Masters degree

in Integrated Water Resources Management (IWRM)

Civil Engineering Department

June 2008

UNIVERSITY OF ZIMBABWE

RELATIONSHIP BETWEEN STREAM BANK CULTIVATION AND SOIL

EROSION IN DEDZA, MALAWI

Supervised by Dr A. Murwira

Dr K.A. Wiyo

Mr A. Mhizha

A thesis submitted in partial fulfillment of the requirements of the Masters degree

in Integrated Water Resources Management (IWRM)

Civil Engineering Department

June 2008

Relationship between stream bank cultivation and soil erosion in Dedza, Malawi

University of Zimbabwe – IWRM MSc Thesis Chimango Mlowoka June 2008 ii

DECLARATION

I, Chimango Mlowoka declare that this thesis is my own work. To the best of my knowledge it

has not been submitted before for any degree at any university.

Signed: ………………………………

Date: …………………………………


University of Zimbabwe – IWRM MSc Thesis Chimango Mlowoka June 2008 iii

DEDICATION

To my husband Bryer, so understanding and supportive

To Favour, Khumbiro and Kunozga, wonderful children you are, for accepting to be deprived of

the support you needed

To dad and mum for continually encouraging me to go for it


University of Zimbabwe – IWRM MSc Thesis Chimango Mlowoka June 2008 iv

ACKNOWLEDGEMENTS

God you have been so faithful. Who am I that you should be mindful of me?

My supervisors, Dr A. Murwira, Dr K.A. Wiyo and Mr A. Mhizha, for the time spent and for

tirelessly working to see this end product. I have been greatly inspired by your hard working

spirit and will forever cherish the contributions you made to this work. God bless you all.

Waternet for believing that a 40 year old would manage the demands of this hectic programme

and granting me scholarship. Extend this opportunity to many more of my calibre.

Civil Engineering staff you did everything possible to encourage me to attain my goal. Your

constructive criticisms have helped to shape me.

Department of Irrigation for releasing me to pursue this programme and for all the assistance

made towards my research. Special thanks to Mr G. Mwepa for your guidance in my research.

Department of Land Resources, Messrs Munthali, Singini and J Mzembe for all the guidance and

maps provided for my work.

Dedza Irrigation staff, Dedza RDP staff and Mrs Kapatsa for being available throughout the

study period.

Farmers along Mwachakula and Namanolo streams for being cooperative. Paul Kanzule,

Shadrech Katsache and Samson Levison for making data collection possible.

Ausward and Annie Zidana God will richly bless your sacrifice.

Hudson and Memory Tchale there would have been no pictures without you. Special thanks also

go to the Mmangisas for entrusting me with their camera.

Jacquiline, Tenele, Mahlalele, Sydney, Mavuto, Chisanga, Tatenda, Hazel, Grace, Regina,

Rennie, Victor, Mattheus, Taurai, what a class you were. You stood by me. I cannot talk of

IWRM without mentioning you folks.

Bryer and children thank you for being available and for every contribution you made as I

struggled to produce a product of worth. How I wished I could give you direction in your home

works. May God richly bless you.


University of Zimbabwe – IWRM MSc Thesis Chimango Mlowoka June 2008 v

ABSTRACT

The main objective of this research was to test whether there is a relationship between the extent

of stream bank cultivation and the extent of soil erosion. Although stream banks have been

cultivated over many years it is hypothesised that the practice is linked to increased levels of soil

erosion. While considerable research has been conducted on the effects of riparian buffers on

water quality and aquatic habitat, little is known about the influence of the removal of riparian

vegetation on stream bank erosion. Therefore this study focused on the effects of stream bank

cultivation on soil erosion. It is hypothesised that the removal of riparian vegetation by stream

bank cultivation amplifies stream bank erosion.

The study aimed at determining the relationship between the number of gardens as a surrogate

for stream bank cultivation and distance away from stream, changes in the extent of stream bank

cultivation over time, significant differences in the extent of soil erosion indicators (changes in

soil surface levels and occurrence of gullies) and the relationship between the extent of

cultivation and the extent of soil erosion indicators. Stream bank cultivation was determined

using overlay analysis in GIS, aerial photographs of 1980, 1982 and 1995 and a SPOT satellite

image of 2002. Soil deposition was determined in 21 sites of sizes between 2.5 and 5.0 m2, using

the erosion pin method and measurements for length, depth and width were taken for 20 gullies.

Bivariate relationships were determined using correlation and non linear regression analyses.

The study revealed that a significant (α=0.05) negative relationship exists between number of

gardens and distance away from the stream with most of the gardens located within 18 metres of

the stream. Within this distance 74 percent of the gardens are under irrigation and 87 percent of

the gardens are without any form of soil conservation measure. 52 percent have no buffer zones

and for those that have buffers the mean width is 3.7 ± 6 metres. Though there is change in area

under cultivation over 22 years there are no significant (α=0.05) differences along the two

streams. Area increased between 1980 and 1982, remained constant until 1995 then decreased

between 1995 and 2002. The study also revealed that though changes in soil surface levels

occurred there was more soil deposition 82.86±104.738 (n = 70) than soil loss 60.96±69.857 (n =

20) along the two streams. However in terms of gulley occurrence no significant (α=0.05)

differences were observed. Whereas there was a significant (α=0.05) positive relationship

between number of gardens and soil deposition there was no relationship between number of

gardens and gulley volumes.

The study concludes that the extent of cultivation is contributing to the extent of soil deposition

along the streams, and this is amplified by irrigation activities and the non use of soil

conservation measures. The study therefore recommends that further studies be done to establish

the origin of the deposited soils to ensure that appropriate mitigation measures are applied. The

study also recommends similar studies over a number of years, under different ecological zones

and different soil characteristics to test if the same relationships would emerge. In addition all

irrigation planning may have to seriously incorporate appropriate soil conservation measures.

The Malawi Government may also need to come up with practical regulations on stream bank

protection and mechanisms for enforcing them considering the current food production-

population imbalances that exist.


University of Zimbabwe – IWRM MSc Thesis Chimango Mlowoka June 2008 vi

TABLE OF CONTENTS

DECLARATION ............................................................................................................................ ii

DEDICATION ............................................................................................................................... iii

ACKNOWLEDGEMENTS ........................................................................................................... iv

ABSTRACT .................................................................................................................................... v

TABLE OF CONTENTS ............................................................................................................... vi

LIST OF FIGURES ..................................................................................................................... viii

LIST OF TABLES ......................................................................................................................... ix

CHAPTER 1: INTRODUCTION .................................................................................................. 1

1.1 Background ........................................................................................................................... 1

1.2 Problem Statement ................................................................................................................ 2

1.3 Justification ........................................................................................................................... 3

1.4 General Objective ................................................................................................................. 3

1.5 Specific Objectives ............................................................................................................... 3

1.6 Null Hypotheses .................................................................................................................... 4

CHAPTER 2 ................................................................................................................................... 5

STREAM BANK CULTIVATION AND SOIL EROSION: A REVIEW .................................... 5

2.0 Introduction ........................................................................................................................... 5

2.1 Stream Bank Cultivation and Soil Erosion ........................................................................... 5

2.2 Stream bank cultivation ........................................................................................................ 6

2.3 Soil Erosion ........................................................................................................................... 7

2.3.1 Soil Erodibility ............................................................................................................... 9

2.3.2 Soil Conservation Measures ........................................................................................ 11

2.4 Summary of Review ........................................................................................................... 12

CHAPTER 3: STUDY AREA ...................................................................................................... 14

3.1 Location .............................................................................................................................. 14

3.2 Rainfall ................................................................................................................................ 16

3.3 Water and Land Resources ................................................................................................. 17

3.4 Soils..................................................................................................................................... 17

3.5 Land Use ............................................................................................................................. 18

CHAPTER 4: MATERIALS AND METHODS .......................................................................... 19

4.1 Introduction ......................................................................................................................... 19

4.2 Data Collection ................................................................................................................... 19

4.2.1 Determination of distance of gardens from stream ..................................................... 19

4.2.2 Determining extent of stream bank cultivation over time ............................................ 21

4.2.3 Determination of changes in soil surface levels .......................................................... 21

4.2.4 Determination of gulley occurrence ............................................................................ 22

4.2.5 Determination of relationship between extent of cultivation and extent of erosion

indicators .............................................................................................................................. 22

4.3 Data Analysis ...................................................................................................................... 23

CHAPTER 5: RESULTS AND DISCUSSIONS ......................................................................... 24

5.1 Relationship between number of gardens and distance from the stream ............................ 24

5.2 Change in extent of area under cultivation over time ......................................................... 28

5.3 Extent of Soil Erosion Indicators ........................................................................................ 32

5.3.1 Changes in soil surface levels ...................................................................................... 32


University of Zimbabwe – IWRM MSc Thesis Chimango Mlowoka June 2008 vii

5.3.2 Gulley count ................................................................................................................. 33

5.3.3 Gulley Volume .............................................................................................................. 33

5.4 Relationship between Extent of Cultivation and Soil Erosion Indicators........................... 38

5.4.1 Relationship between number of gardens and changes in soil surface level ............... 38

5.4.2 Relationship between number of gardens and gulley volumes .................................... 44

5.5 Summary of findings and discussions................................................................................. 49

CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS ................................................ 53

6.1 Conclusions ......................................................................................................................... 53

6.2 Recommendations ............................................................................................................... 53

REFERENCES ............................................................................................................................. 54

APPENDIX 1 ................................................................................................................................ 62

APPENDIX 2 ................................................................................................................................ 65

APPENDIX 3 ................................................................................................................................ 66

APPENDIX 4 ................................................................................................................................ 80


University of Zimbabwe – IWRM MSc Thesis Chimango Mlowoka June 2008 viii

LIST OF FIGURES

Figure 3.1 Location of Dedza District .......................................................................................... 14

Figure 3.2 Location of Mwachakula and Namanolo Streams in Dedza District .......................... 15

Figure 4.1: Study design showing streams, gardens, gullies and plots for soil surface level

changes determination along Mwachakula and Namanolo streams ............................................. 20

Figure 5.1: Relationship between number of gardens and distance away from stream ................ 24

Figure 5.2: Comparison between number of gardens based on a threshold of 18 metres ............ 26

Figure 5.3: Number of gardens along Mwachakula and Namanolo streams ................................ 27

Figure 5.4: Number of gardens with and without irrigation within 18 metres of the stream ....... 28

Figure 5.5: Number of gardens with and without conservation within 18 metres of the stream .. 29

Figure 5.6: Area under cultivation along Mwachakula and Namanolo from 1980 to 2002 ......... 30

Figure 5.7: Total area under cultivation between 1980 and 2002 ................................................. 31

Figure 5.8: Proportions for area under stream bank cultivation over time ................................... 31

Figure 5.9: Extent of cultivation along Mwachakula and Namanolo streams over time .............. 32

Figure 5.10/11: Soil deposition along Mwachakula and Namanolo ............................................. 34

Figure 5.12/13: Comparison of soil deposition............................................................................. 34

Figure 5.14: Mwachakula downstream ......................................................................................... 35

Figure 5.15: Mwachakula upstream .............................................................................................. 35

Figure 5.16/17 Upstream downstream soil loss ............................................................................ 36

Figure 5.18: Upstream downstream soil loss

Figure 5.19 Upstream downstream soil deposition....................................................................... 36

Figure 5.20: Number of gullies along 200m stretches of different stream segments ................... 37

Figure 5.21: Gulley volumes along Mwachakula and Namanolo streams ................................... 37

Figure 5.22/23 Gulley volumes less than 10m3 ............................................................................ 39

Figure 5.24/25: Number of gardens and soil loss ......................................................................... 40

Figure 5.26: Soil loss/ threshold of 10 gardens

Figure 5.27: Soil deposition/threshold of 10 gardens ................................................................... 41

Figure 5.28: Number of irrigated gardens and soil deposition ..................................................... 42

Figure 5.29: Number of rain-fed gardens and soil deposition ...................................................... 42

Figure 5.30: Soil deposition and irrigated gardens

Figure 5.31: Soil deposition and rain-fed gardens ........................................................................ 43

Figure 5.32: Number of conserved gardens and soil deposition ................................................... 44

Figure 5.33: Number of un-conserved gardens and soil deposition ............................................. 45

Figure 5.34: Soil deposition along conserved gardens ................................................................. 45

Figure 5.35: Soil deposition along un-conserved gardens ............................................................ 46

Figure 5.36: Volumes < 10 m3 and number of gardens ............................................................... 47

Figure 5.37: Volumes >10 m3 and number of gardens ................................................................ 47

Figure 5.38/39: Gulley volumes based on threshold of 9 gardens ................................................ 48

Figure 5.40: Volumes < 10 m3 and gardens without conservation

Figure 5.41: Volumes >10 m3 and gardens with conservation 50

Figure 5.42: Volumes <10m3 based on threshold of 9 gardens

Figure 5.43: Volumes >10m3 based on threshold of 9 gardens 51

Figure 7.1: Observed buffer widths along Mwachakula and Namanolo Streams ........................ 64

Figure 7.2: Collapsing of banks along Mwachakula leading to loss of garden area .................... 65

Figure 7.3: Collapsing of banks planted to elephant grass ........................................................... 80


University of Zimbabwe – IWRM MSc Thesis Chimango Mlowoka June 2008 ix

LIST OF TABLES

Table 3.1: Rainfall intensity duration for Central Lakeshore Plains and Escarpment ................ 16

Table 3.2: Rainfall amounts for Dedza RTC ................................................................................ 16

Table 3.3: Average Rainfall and number of rainfall events covering study period ...................... 17

Table 3.4 Soils of Dedza Escarpment ........................................................................................... 18

Table 4.1: Description of stream segments based on stream morphology ................................... 19

Table 7.1: Irrigation Technologies Used ...................................................................................... 62

Table 7.2: Conservation Measures Used ...................................................................................... 62

Table 7.3: Observed Buffer Widths (m) ........................................................................................ 63

Table 7.4: Area under cultivation from 1980 to 2002 .................................................................. 65

Table 7.5: Soil Texture differences ............................................................................................... 66

Table 7.6: Bulk Density differences .............................................................................................. 66

Table 7.7: Organic Matter differences ......................................................................................... 66

Table 7.8: pH differences .............................................................................................................. 67

Table 7.9: Cation Exchange Capacity differences ....................................................................... 67

Table 7.10: Soil deposition and soil texture correlation .............................................................. 68

Table 7.11: Soil deposition and organic matter correlation ........................................................ 68

Table 7.12: Soil loss and soil texture correlation ......................................................................... 69

Table 7.13: Soil loss and organic matter correlation ................................................................... 69

Table 7.14: Correlation between 10m3 gullies, number of gardens and soil properties at 20cm

depth .............................................................................................................................................. 70


depth .............................................................................................................................................. 71


depth .............................................................................................................................................. 72


depth .............................................................................................................................................. 73


depth .............................................................................................................................................. 74

Table 7.19: Correlation between above 10m3 gullies and soil properties at 20cm depth ............ 75




Table 7.23: Correlation between above 10m3 gullies and soil properties at 100cm depth .......... 79


University of Zimbabwe – IWRM MSc Thesis Chimango Mlowoka June 2008 1

CHAPTER 1: INTRODUCTION

1.1 Background

It is widely recognized that accelerated erosion is one of the major factors responsible for soil

degradation. Mismanagement, neglect and exploitation can ruin the fragile resource and become

a threat to human survival. Annual global loss of agricultural lands due to soil erosion is about 3

million hectares. Soil erosion has destroyed 430 million hectares of productive lands since the

beginning of settled agriculture. Human induced soil degradation has affected 24 % of the

inhabited land area of the world. The values for the individual continents range from 12 % in

North America, 18 % in South America, 19 % in Oceania, 26 % in Europe, 27 % in Africa and

31 % in Asia (Woreka, 2004).

Environmental degradation in the Zambezi basin is a visual testimony of the self destructiveness

of an impoverished agricultural sector. The ‘food production-population imbalance’ of the basin

is leading to production increases through the opening up of new and sometimes marginal land

as well as intensification of agricultural production. Without adequate agricultural yields to

secure their livelihood, farmers are expanding into environmentally fragile areas. In Zimbabwe

more and more people are being forced to settle along river beds, in mountainous areas, grazing

areas and fragile lands, exacerbating environmental problems in the country (SADC-ELMS and

WSCU, 2000).

Siltation of rivers and streams due to soil erosion is an issue of great concern in Malawi.

Population pressure on arable land has led to the encroachment of marginal land which usually

has very steep slopes, and therefore classified as unsuitable for arable use. This has contributed

significantly to land degradation due to accelerated soil erosion as a result of runoff (Nyirongo,

2001). Land pressure is so high in Malawi that it has forced 28% of marginal or unsuitable land

into cultivation. In addition smallholder farmers do not practice soil and water conservation

technologies, thereby amplifying the soil erosion problems (SADC-ELMS and WSCU, 2000).

By and large the majority of crops grown in Malawi are poor cover crops and this makes most of

the cultivated land vulnerable to erosion by water. The government of Malawi (both colonial and

current) has always been aware of the need to conserve land resources in order to attain sustained

productivity (Kasomekera, 1992).

Stream bank cultivation is a practice that involves growing of crops along banks of streams. The

history of Malawi as reported by Peters (2004) indicates that stream banks have been cultivated

over many years and that they have high potential for small scale irrigation. This is consistent

with Kamthunzi (2000) and Saka, Green and Ng’ong’ola (1995) who report that such informal

irrigation in Malawi has been practiced for many decades. Farmers cultivating along stream

banks use simple methods for bringing the water to the fields (Kamthunzi, 2000) and these

include technologies like treadle pumps and watering cans. These technologies are best used

where availability of shallow ground water levels are guaranteed. Kadyampakeni (2004) reports

that currently in Malawi there is a national interest in utilization of dambos (seasonally

waterlogged bottom lands) and as such growing of maize, legumes and vegetables for food

security, nutrition and poverty alleviation of the rural poor is being promoted. That is why

wetlands and river banks in some parts of Malawi are extensively used for growing irrigated



crops (Kamthunzi, 2000). Farmers use these stream banks in order to spread risk of crop failure

arising from vagaries of nature and other hazards (Mangisoni and Nankumba, 1999 in

Kadyampakeni, 2004). Stream bank cultivation thus provides an opportunity for smallholder

farmers to either supplement their rain fed crops or grow for sale to improve their incomes. The

average field sizes for these stream bank gardens range from 0.1 to 0.4 hectares (Kamthunzi,

2000).

Recent droughts and insufficient rainfall have greatly affected agricultural production in Malawi

such that Government has as a consequence put great emphasis on developing irrigated

agriculture to bridge these periods of drought and insufficient rainfall and increase food security

(Kamthunzi, 2000). In particular droughts experienced in 1991/92 rekindled interest in irrigated

agriculture (Saka, Green, and Ng’ong’ola, 1995). Thus there is a push for less dependence on

rain fed agriculture only and more on irrigation farming. According to Peters (2004) stream

banks have become areas of highest value for Malawi because water can be accessed year-round,

especially considering the fact that Malawi is a land–scarce country with a single annual rainfall

period.

Kamenyagwaza in Dedza is characterized by bare recent erosion surfaces and as such has often

infertile soils in the upper slopes. These uplands have thin acidic soils that limit production of

many crops (aluminium sulphate soils). However the river valley bottoms have residual moisture

where extensive stream bank cultivation takes place. Because of high erosion rates in the

uplands, soils are less fertile but valley bottoms are very fertile and have residual moisture.

Farmers have taken advantage of this by establishing gardens in the dambos (seasonally

waterlogged bottom lands) called dimbas (Wiyo, 2007).

1.2 Problem Statement

Siltation of rivers and streams due to soil erosion is an issue of great concern in the world and

Malawi in particular. It is negatively impacting on aquatic life, hydro-electricity production,

water quantity and quality. Although stream bank cultivation has been linked to increased levels

of soil erosion, there still remains a gap on quantifying the extent of the practice and its impacts

on erosion. Currently there is need to expand the limited knowledge regarding the practice so as

to mitigate the potential negative impacts of the practice. It has also not been ascertained to what

extent stream bank cultivation is related to the soil erosion occurring along stream banks. It is in

this regard that this study seeks to establish whether there is a link between the extent of

cultivation along stream banks and the soil erosion occurring along the banks.

While considerable research has been conducted on the effects of riparian buffers on water

quality and aquatic habitat, little is known about the influence of the removal of riparian

vegetation on stream bank erosion (Wynn, 2004). Though Malawi has regulation regarding

maintaining a non-cultivated buffer zone along the streams, Matiki, (2005) observes that there is

no enforcement of such regulation. He further observes that Non Governmental Organisations

and Government Ministries have no clear stand on the practice. The problem is amplified by the

fact that the Government Agencies responsible for irrigation have no mandate to enforce the law.



1.3 Justification

This study uses Malawi as a case study. Malawi is characterized as one of those countries with

the highest level of soil erosion in sub Saharan Africa (Nakhumwa, 2004). Erosion has been

identified by a variety of researchers and policy makers as the most serious environmental

problem in Malawi, as evidenced by references in the National Environmental Action Plan, the

State of the Environment Report, and numerous World Bank and other donor-sponsored studies

(Bonda, Mlava, Mughogho and Mwafongo, 1999).

The World Bank (Environmental Affairs Department, 2002) estimates that most districts in

Malawi have a rate of soil loss above the rate of soil formation that is 12 tonnes per ha per year

and that Dedza, a district within Lilongwe Agricultural Development Division has an erosion

level of 22 tonnes per ha per year. In 1994 Kasungu and Lilongwe Agricultural Development

Divisions (ADD) each lost 5 million tonnes of top soil (Environmental Affairs Department,

2002). Traditional Authority Kamenyagwaza’s area is characterized by bare recent erosion

surfaces often with infertile soils in the upper slopes. The steep slopes and the rugged terrain

means there is higher potential for erosion and soil fertility loss (Wiyo, 2007).

State of Environment Report of 2000 reports on diminishing base flows that have been

experienced in recent years in some rivers like Bua, which completely dried up from 1994 to

1997. This has been attributed to siltation of the river arising from expansion of agriculture in

Central Malawi. Rural water supply schemes have streams as their sources of supply. The

catchments of some of these streams are under intensive cultivation often without adequate

conservation measures (Environmental Affairs Department, 2001).

The Revised Water Resources Act is currently being tabled in Parliament. Once the Act has been

approved line ministries concerned will be required to come up with regulations concerning

stream bank protection, among other issues. The results from this study could therefore be

considered a potential input in formulation of some of these regulations.

1.4 General Objective

To test whether the extent of stream bank cultivation is related to the extent of soil erosion

indicators, namely, change in soil surface levels and gulley occurrence along Mwachakula and

Namanolo streams

1.5 Specific Objectives

1. To determine the relationship between the number of gardens and distance away from the

stream along Mwachakula and Namanolo streams.

2. To determine changes in the extent of stream bank cultivation along Mwachakula and

Namanolo streams over time

3. To determine whether there are significant differences in the extent of soil erosion

indicators (changes in soil surface levels and occurrence of gullies) along Mwachakula

and Namanolo streams.



4. To determine whether there is a relationship between the extent of cultivation and the

extent of soil erosion indicators along Mwachakula and Namanolo streams.

1.6 Null Hypotheses

1. There is no significant relationship between number of gardens and distance away from

the stream along Mwachakula and Namanolo streams.

2. There is no significant change in the extent of stream bank cultivation along

Mwachakula and Namanolo streams over time.

3. There is no significant difference in the changes in soil surface levels along Mwachakula

and Namanolo streams.

4. There is no significant difference in the occurrence of gullies along Mwachakula and

Namanolo streams.

5. There is no significant relationship between the extent of cultivation and the extent of

soil erosion indicators along Mwachakula and Namanolo streams

The report of this study is presented in six chapters. Based on field observations in the study area

the stream bank has been defined as the area bordering the stream within a distance of 50 metres

from the stream centre. Chapter 1 introduces the study by giving a background to the occurrence

of stream bank cultivation and soil erosion and their importance to the world at large, including

Malawi in particular. The chapter also presents the justification for carrying out the study.

Chapter 2 follows with a review on the relationship between stream bank cultivation and soil

erosion. The study area is presented in Chapter 3, showing the location and highlighting

characteristics of interest to the study. Materials and methods are discussed in Chapter 4 also

presenting the study design, the use of geographical information systems in determining extent of

stream bank cultivation and the use of the pin erosion method and gulley volume determination

in determining extent of erosion indicators. Chapter 5 presents results and discussion for each of

the objectives of the study. Chapter 6 concludes the findings including the significant

relationships and differences emerging from the bivariate analyses conducted. Finally the chapter

gives recommendations based on the findings.



CHAPTER 2

STREAM BANK CULTIVATION AND SOIL EROSION: A REVIEW

2.0 Introduction

This chapter presents a review of literature on cultivation occurring along stream banks and how

it is related to soil erosion in different parts of the world. The review initially focuses on how

cultivation along stream banks has impacted on soil erosion. This is followed by a review on

importance of stream banks and existing regulations on their protection. Finally processes of soil

erosion are reviewed including factors contributing to their occurrence. The review addresses the

need for coming up with mitigation measures regarding the soil degradation occurring world

wide and in particular Malawi.

2.1 Stream Bank Cultivation and Soil Erosion

The world map of the status of Human Induced Soil Degradation (GLASOD, 1990 as cited in

Douglas, 1994) estimates that a quarter of the world’s agricultural land is already seriously

damaged by soil degradation. Irrespective of specific figures what is clear is that the world’s

arable land resources are finite and are coming under increasing pressure from a growing world

population and land degradation. The world’s population is currently believed to be increasing

by 2 % per year (more in developing countries). However in order to maintain and improve

nutrition and health agricultural production will need to increase by at least 3 % per year for the

next 50 – 100 years (Douglas, 1994).

Intensification of agriculture will be necessary to feed the earth’s expected 10.5 billion

inhabitants by the year 2110. Rather than intensification of agriculture per se, it is the

mismanagement, inappropriate land use, and indiscriminate and excessive use of some input that

cause ecological and environmental problems (Lal, Eckert and Logan, 1988). Agricultural

practices denude the bank of vegetation thereby causing stream bank erosion (Thompson and

Green, 1994). Over clearing of catchment and stream bank vegetation, and poorly managed sand

and gravel extraction are examples of management practices which result in accelerated rates of

bank erosion (Department of Natural Resources and Water, 2006). Cropping too close to both

stream banks has led to bank erosion problems (Wall, Baldwin and Shelton, 2003) and is likely

to cause siltation due to erosion (Zidana, 2008). Accelerated soil erosion is a symptom of land

misuse, and has become a major concern since intensification of conventional agricultural

practices on marginal lands (Lal, Eckert and Logan, 1988). Certain crops can be characterized as

leading to more soil erosion under conventional methods of cultivation than others (Nakhumwa,

2004).

Since the onset of agriculture, stream banks have been continually degraded. In the continental

U.S. today, over half of the wetland and riparian zones have been destroyed. The destruction of

these zones has created numerous problems, resulting in the partial or complete destruction of

the immediate stream habitat, as well as destruction of the vitality of areas further downstream

(Hayes-Conroy, 2000). Due to land degradation, there is continued and accelerating soil erosion

in many parts of the Zambezi Basin leading to siltation of water sources. Marginal areas are

sometimes cultivated to meet the food requirements of the poor. The exploitation of marginal



land including wetlands, stream banks and hill slopes contradicts one of the SADC objectives,

which emphasizes that the utilization of natural resources requires good management and

conservation (SADC-ELMS and WSCU, 2000).

Streambank erosion is very common and often blamed on cultivation along the stream banks

(Saka, Green, and Ng’ong’ola, 1995). Mogaka, Gichere, Davis and Hirji (2005) suggest that

stream banks are unsuitable areas for cultivation because their use has led to considerable soil

loss. FAO, AGL (2000) observed that in Zimbabwe very rapid erosion was occurring where

agriculture has taken place. However Kerr (2002) reporting on stream bank cultivation in

Malawi, could not relate the practice to the erosion observed along the banks but rather observed

that some of the gardens along the streams did not seem to be contributing to the bank erosion.

2.2 Stream bank cultivation

Stream banks are located within riparian zones. A riparian zone, strictly defined, comprises only

the vegetation in a stream channel and along the river banks; however, the term has recently been

used more broadly to include the part of the landscape adjacent to a stream that exerts a direct

influence on stream and lake margins and the water and aquatic ecosystems associated with

them. Many subsistence and income-generating activities that are integral parts of rural

household economies are undertaken in riparian zones. Relatively flat topography and the

availability of water for irrigation make riparian land attractive for cultivation (Vigiak, Ribolzi,

Pierret, Valentin, Sengtaheuanghoung and Noble, 2008).

Lands along streams and rivers are distinct environments usually with greater soil moisture, and

soil fertility than surrounding land. This makes them productive environments with many plants

particularly adapted to this niche. The productivity of stream banks makes them vulnerable to

over-use and to practices that cause them to deteriorate, creating additional problems (Land and

Water Australia, 2006). Retention of naturally vegetated buffer strips along streams is probably

the best-known and most widely useful category of best management practices (U.S.

Environmental Protection Agency, 2007). Matthee (1984) suggests that a certain width of land

must be regarded as the preserve of the stream, where encroachment on this area can result in

severe damage, and even changes in the course of the stream. Franklin Conservation

Commission (2006) considers 100 feet (31 metres) from a defined/delineated resource area as the

buffer zone and consequently an additional protected resource.

In general, riparian buffer zones can be defined as green zones along streams, rivers, and lakes

(Hayes-Conroy, 2000). NOREC (2005) defines a buffer zone as a grassed or an uncultivated,

vegetation-covered zone (or strip) used to separate fields and constructed areas from bodies of

water. The permanent vegetation on the zone protects banks and littoral zones from erosion and

from the leaching of nutrients, microbes and pesticides to the water. According to an

environmental programme in Finland, 1-m-wide headlands and 3-m-wide buffer strips with

permanent vegetation are normally established on the sides of main ditches and watercourses

respectively. Buffer zones (minimum width 15 m) are used on steep sloping shoreline fields and

flood retention areas to prevent erosion and transport of nutrients (Jaana, 2006). NOREC (2005)

reports from a study by Rekolainen (1992) that simulated tests employing the CREAMS model

have shown that a buffer strip of 1 to 3 metres can already absorb half the sediment load deriving

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from mineral soils. However on clayey and silty soils a buffer zone of 5 to 10 metres is needed to

remove the same amount of sediment. Syversen (2005) reports that vegetated buffer zones

adjacent to a stream can effectively remove and retain nutrients and sediments as shown by

results from her study where there was significantly higher removal efficiency (in %) from 10 m

wide buffer zones compared to 5 m widths. The efficiency of buffer zones in removing

suspended solids and nutrients is affected by the width of the zone, gradient of the drained field,

soil type and particularly by the variety and density of zone vegetation (NOREC, 2005). Buffer

zone width also strongly influences soil loss. In a study comparing effectiveness of buffer zone

widths results showed that 20m and 90m buffer zones reduced sediment leaving the watershed

by 18% and 52% respectively when compared to a no buffer zone (Vanderwel and Jedrych,

2005).

When riparian vegetation is removed and replaced by agricultural crops, the banks become more

exposed to effects of rainfall and overland flow, depending on the type of crops grown (Ott,

2000). According to Vanderwel and Jedrych (2005) growing crops or grazing livestock too close

to a water body reduces bank stability and increases the risk of sediments and nutrients. Matthee

(1984) likewise observes that river banks are denuded by the cultivation of ground too near the

stream. The Zimbabwe Stream Bank Protection Act of 1952 prohibits cultivation within 30m of

stream (Matiza, 1992). This legislation, which was both riparian and agricultural in nature, was

couched in conservationist terms. It was initiated by problem of soil erosion on European

commercial farmland. Moreover, like much legislation of its kind in Africa during this period, it

was based on the most limited empirical testing (Watts, 1989 in Bell and Hotchkiss, 1991).

According to Wenner (1981), the Amended Agricultural Act 1981 of Kenya prohibits cultivation

near valleys of gullies and rivers and recommends a strip of grass or natural vegetation, at least

1m wide between the cultivated area and the gulley or river bank. Bell and Hotchkiss (1991)

observed that location of gardens along streams was based on estimates of the availability of

good soil and water. However in some areas cultivable land lies close to the water courses so that

on the basis of technically objective measurement, no land would be available for cultivation

outside the 30m limit. Peters (2004) observes that the colonial administrators in Nyasaland

(Malawi) and Southern Rhodesia (Zimbabwe) tried to forbid the use of stream banks, often with

little success. The prohibitive legislation still exists but it is not well enforced (Matiza, 1992).

(Wiyo, 2007) in a study carried out in Dedza discourages cultivation very close to the stream or

river, recommending a 5m buffer minimum, and in addition encourages planting of trees along

the river/stream banks.

2.3 Soil Erosion

Soil erosion is the removal of soil particles from a site and can be caused by forces of water

among other agents (Iowa Department of Natural Resources, 2006). Soil erosion by water is the

major cause of soil degradation on the planet earth. It has recently been estimated that millions of

hectares of cultivated land are lost to agricultural production each year because of soil

degradation. As the earth’s population increases, soil degradation inevitably leads to reduced

food supplies for those that inhabit this planet. The scale of soil degradation is difficult to grasp,

but at least a billion hectares of the earth’s soil has been seriously degraded because of water

erosion. The estimated costs of water erosion exceed $400 billion dollars per year (Laften and

Roose, 1998). Indirect costs of erosion include siltation of streams (Barrow, 1991). Soil erosion



is one form of soil degradation along with soil compaction, low organic matter, loss of soil

structure, poor internal drainage, salinisation, and soil acidity problems. These other forms of

soil degradation, serious in themselves, usually contribute to accelerated soil erosion. According

to Lang (2001) human activity often multiplies erosion greatly, both in frequency and size and it

becomes very common on certain soils when farmed. Soil erosion may be a slow process that

continues relatively unnoticed, or it may occur at an alarming rate causing serious loss of topsoil

(Wall, Baldwin and Shelton, 2003). Among various causes of land resources degradation, soil

erosion ranks high in tropical climates especially in cases of extensive agricultural production as

is the case in Malawi (Kasomekera, 1992).

Where land use causes soil disturbance, erosion may increase greatly above natural rates

(International Union of Geological Sciences, Undated). Many of the land use practices adopted

in the developing countries appear to be consistent with measures that transform topsoil into a

non-renewable resource (Anderson and Thampapillai 1990). Bunderson, Jere, Hayes and

Phombeya (2002) report, based on World Bank (1992), that loss of top soil in Malawi averages

over 20 tons/ha per annum with rates more than 50 tons/ha in many areas as also reported by

Bishop(1992) quoted in Nakhumwa (2004).

Stream bank erosion comes about when streams and rivers cut horizontally into their banks

(Matthee, (1984). It occurs when streams begin cutting deeper and wider channels as a

consequence of increased peak flows or the removal of local protecting vegetation, leading to

increase in stream sediment and suspended material (Department of Primary Industries, 2007).

When banks start eroding the soils are deposited into the streams. Over time these soil deposits

accumulate and reduce the streams’ carrying capacity, which has a bearing on water availability

for different users in the catchment (Ott, 2000). Rain falling on stream banks or runoff from

adjacent fields that enters a stream by flowing over the stream banks can also erode soil from

stream banks, particularly if the banks are inadequately protected (Iowa Department of Natural

Resources, 2006). In Morocco, for example, the bulk of sediment is now thought to originate

from stream bank erosion and not from erosion on agricultural land (Pagiola, 1999). Stream

banks are a source of sediments (Onstad, Mutchler and Bowie, 1977) especially in watersheds

with changing land use and limited riparian protection (Jennings and Harman, 2001). A study on

erosion estimates carried out in Iowa by Schilling and Wolter (2000) suggests that stream banks

contribute about 50 percent of the annual suspended sediment load in the channel. This concurs

with Zaimes, Schultz, and Isenhart (2004) who quoting Lawler et al., (1999) indicate that stream

bank erosion can supply over 50% of the sediment in streams, the percentage depending on the

adjacent land-use and vegetation cover. However U.S. Environmental Protection Agency (2007)

report that although sediment may enter a river from adjacent banks, most is transported from

upstream sources. Land lost by stream bank erosion is gone forever. Moreover it is usually

productive alluvial bottom soils which are lost (Matthee, 1984).

Wenner (1981) defines gullies as an advanced occurrence of erosion where rills cannot be

smoothed out by ordinary tillage. Gullies are a major source of land degradation, their presence

is a strong indicator that erosion is out of control and that the land is entering a critical phase that

threatens its productivity (Laften and Roose, 1998). Gullies are the most spectacular

manifestations of soil erosion (Matthee, 1984). Caused by channel erosion, they are an

impediment to farming, as well as a serious degradation of the soil resource. Gullies are the



visible erosion process that alerts the observer to the existence of a threat to the sustainability of

a land resource due to water erosion (Laften and Roose, 1998).

Gulley erosion is the visible manifestation of poor land use practices which have resulted in an

increased volume and velocity of rainfall runoff water (Armour and Russell, 1997). General

gulley erosion and sedimentation of waterways are considered problems exported off the

farmers’ land and constitute off farm site costs. Napier has suggested that off site costs of soil

erosion are likely to be more important than on site damages in low income countries (Norman

and Douglas, 1994).

According to Wenner (1981) gullies develop particularly in soils between clay and sand, that is,

loam and silt because clay is erosion resistant, and because water infiltrates in the sand rapidly.

Gullies commonly occur in the cultivated land on paths representing garden boundaries which

usually run up and down slope (Saka, Green, and Ng’ong’ola, 1995). Once established gullies

are often difficult to control, and a gulley system may grow to cover a considerable area. Gullies

are usually responsible for contributing a large proportion of the sediment load of streams and

rivers (Gossage and Selenje, 1994).

The two most important factors which contribute to the statistical variation in erosion are soil

type and population density. There is a direct positive correlation between increases in the extent

of eroded terrain, soil type and increases in population density (Environmental Software and

Services GmbH AUSTRIA, 2002).

2.3.1 Soil Erodibility

The erodibility of a soil means its degree of vulnerability to erosion. Some soils will erode more

easily than others in the same conditions of slope, crop and land management, and rainfall

(Matthee, 1984). The susceptibility of any soil type to erosion depends upon the physical and

chemical characteristics of the soil, in addition to its protective vegetative cover, topographic

position (slope length and gradient), the intensity of rainfall, and the velocity of runoff water

(McCombs, 2007). However erosion and the risk of erosion are difficult to measure directly.

Other soil properties that affect erosion and can change with management, including soil surface

stability, aggregate stability, infiltration, compaction and content of organic matter, can be

measured. Measuring these properties can shed light on the susceptibility of a site to erosion.

Comparing visual observations along with quantitative measurements to the conditions indicated

in the ecological site description or a reference area helps to provide information about soil

surface stability, sedimentation, and soil loss (USDA, Natural Resources Conservative Service,

2001). While social and economic factors markedly affect how land is used, it is its inherent

features which determine its basic potential for long continued production in the face of

destructive forces of erosion (Ministry of Agriculture and Natural Resources, 1994).

Texture

Soil erodibility is an estimate of the ability of soils to resist erosion, based on the physical

characteristics of each soil. Generally, soils with faster infiltration rates, higher levels of organic

matter and improved soil structure have a greater resistance to erosion. The degree of soil erosion



by water depends on the strength of soil aggregates to withstand raindrop impact and surface

flow (Shiralipour, Undated). Where erosion by surface flow is considered sand, sandy loam and

loam textured soils tend to be less erodible than silt, very fine sand, and certain clay textured

soils because the former have higher infiltration rates (Wall, Baldwin, and Shelton, 2003).

However where erosion due to rainfall impact is considered soils which contain a large

percentage of fine sand and silt are more erodible than soils with a high percentage of clay and

coarse sand (Matthee, 1984). In a study by Schjonning (1994) determining the erodibility of

different soils the results showed a clear trend of decreasing soil loss with increasing clay

content.

Bulk Density

Soil compaction can reduce crop yields, and increase runoff and associated soil erosion into

surface waters. This is why soil density is often included among the measurements to determine

how good the soil is for crop growth and to maintain water quality. Producers often identify soil

compaction as a soil quality concern. Therefore, bulk density is usually included in the minimum

data sets used to evaluate crop and soil management practices. (Logsdon, Sally, Karlen, Douglas,

2008). Babolola and Lal (1977), as quoted by Nakhumwa (2004), report that bulk density affects

water infiltration, root growth and uptake of nutrients and water. Soil erosion is a complex

phenomenon that depends primarily on soil bulk density (Journal of the American Water

Resources Association 2006). From a study carried out by Mokma and Sietz (1992) results

showed that bulk density increased with increasing degree of erosion. The increasing bulk

density probably reflects a more dense structure resulting from higher clay content and lower

organic matter content of the eroded soils as suggested by Frye and associates (Mokma and

Sietz, 1992).

Organic Matter Content

Morgan (1985c) in Boardman and Evans (1994) showed that there was some evidence that a

decrease in the organic matter content of soils made them more susceptible to degradation and

erosion. This concurs with the findings of Barrow (1991) who reports that once top soil is

removed, often the sub soil may become more vulnerable to erosion because the lack of organic

matter in sub soil makes a protective vegetation cover more difficult to establish and unless the

sub soil is clay-rich there is less to bind particles together. Matthee (1984) similarly reports that

soils with high organic matter content are more resistant to erosion or in other words, have a

lower erodibility. So it follows that soils with less than 2% organic matter content and soils with

less than 5% clay content are vulnerable to erosion (Barrow, 1991). According to Greenland

(1977) as quoted by Ternan, Williams, and Tanago (1994) soils with less than 3.5% organic

matter are most vulnerable to erosion because of the lack of organic polymers or binding agents.

This is consistent with Ng’ong’ola (1985) who reports that most plants grow well in soils of the

range of 2 to 4 % organic matter content. Soil fertility in Malawi occurs mainly in the top soil

and largely depends on organic matter content. Lack of organic matter accelerates erosion and

increases soil compaction (Environmental Affairs Department, 2002)

http://www.ars.usda.gov/pandp/people/people.htm?personid=3418

http://www.ars.usda.gov/pandp/people/people.htm?personid=2941



Soil pH

Soil pH refers to the level of acidity in a soil. Agricultural practices tend to lower the pH of soils

over time; making them more acidic (Ministry of Agriculture, Food and Rural affairs, 2008). Soil

pH is a characteristic that is indicative of soil erosion. It decreases with increased severity of

erosion (Mokma and Sietz, 1992; F. B. S. Kaihura, I. K. Kullaya, M. Kilasara, J. B. Aune, B. R.

Singh and R. Lal, 1999). The stability of aggregates in the surface soil is crucial to the processes

of soil erosion and runoff generation in agricultural lands. In a study to determine relationships

between aggregate stability and selected soil properties in a humid tropical environment it was

found that there was a significant linear correlation between pH and soil aggregate stability index

indicating that low pH values were evident where the soils were less aggregated (Idowu, 2007).

Cation Exchange Capacity

Cation exchange capacity is the amount of exchangeable cations bound to clay minerals and

humus materials in the soil; e.g. Ca2+

, Mg2+

, K+, Na

+, NH

4+, H

+. Cation exchange capacity gives

indications of the soil's ability to bind and store nutrients. This binding capacity, or nutrient

storage capacity, depends on the type and amount of clay minerals, humus amounts, and pH

values (Senate Department for Urban Development, 1998). Soil pH is important for CEC

because as pH increases (becomes less acid), the number of negative charges on the colloids

increase, thereby increasing CEC (NSW Department of Primary Industries, 2005). Increased clay

content also increases CEC (Mokma and Sietz (1992). A study of soil and sediment quality

indicators in different land uses revealed that CEC decreased with increased land degradation

(Yousefifard, Jalalian, Khademi and Ayoubi, Undated).

2.3.2 Soil Conservation Measures

Norman and Douglas (1994) note from a report by FAO (1986) that in many low income

countries, no policies exist to encourage soil conservation, while rapidly increasing populations

are putting pressure on the land resource base. Environmentally sound traditional practices

attuned to low population densities have been unable to adjust rapidly enough to the decreasing

land per resident ratios, resulting in practices that are environmentally damaging. It is also worth

noting that Bishop (1992), as quoted by Nakhumwa (2004), reports that farmers behave as if they

value short term profits obtained from activities which degrade the soil more highly than they

value the benefits of soil conservation. Legislation can contribute to achieving soil conservation.

However, the best results are likely to be obtained when landowners and users come to realize

that misuse of land is socially unacceptable and economically detrimental (Hauck, 1985).

From hydrological literature it is known that a decrease in soil conservation practices leads to

increased sediment yield from catchments. High soil erosion rates cause high rates of sediment

carried by rivers. Higher sediment yields increase siltation problems (Consulting Engineers

Zimbabwe-Norway, 1985). One of the most important improvements necessary to change the

status of the land is the use of appropriate soil conservation measures (Saka, Green, and

Ng’ong’ola, 1995). Although bamboo is sometimes planted in riparian areas to conserve soil and

water, a Southeast Asian study suggests that it may not be the best ground cover for this purpose

(Vigiak, Ribolzi, Pierret, Valentin, Sengtaheuanghoung and Noble, 2008). The major problem, at



least for Malawi, has been that most of these soil conservation measures were promoted with one

specific aim: to control erosion caused by surface runoff. Later research showed that a major

cause of erosion in the SADC is not surface runoff but raindrop impact and hence the need for

stressing biological control measures and not physical control measures (Shaxton et al, 1989 in

Wiyo, 1999).

In the colonial period, before 1964, soil conservation was characterized by coercive methods to

force farmers in Malawi adopt the alien resource conservation technologies which were

principally European or British oriented. In spite of all the efforts to persuade smallholder

farmers to conserve their over cultivated lands, some careless traditional cultivation practices are

still being witnessed in many parts of the country, with consequences of soil erosion and low

productivity of the soils (Mangisoni, 1999 in Nakhumwa, 2004). Zidana (2008) also reports that

most farmers along Lilongwe and Linthipe rivers cultivate along the banks without conserving

the soils resulting in soil erosion which leads to flooding, siltation, land slides and loss of arable

land. The study also found out that, farmers along these rivers lack trees like Acacia galpini,

Acacia polycantha, Faidherbia albida, shrubs like Sesbania sesban and grass like vetiver, napier

that can be used for river bank protection since the river banks are prone to soil erosion.

Nakhumwa (2004) quoting Mangisoni (1999) and Kumwenda (1995) notes that though small

scale soil conservation techniques are both affordable to smallholder farmers and quite effective

in reducing soil erosion there are low adoption levels of the technologies among smallholder

farmers in Malawi which becomes a major limitation for the farmers. Without any meaningful

increase in the number of smallholder farmers adopting soil conservation and, willingness to

intensify use of these technologies, soil erosion would continue to undermine agricultural

production in Malawi leading to serious food shortage (Nakhumwa, 2004).

The key to successful erosion prevention is the maintenance of a good vegetative cover over the

soil surface. This minimizes or prevents rainfall impact, and helps to maintain the infiltration

capacity of the soil’s surface (Ministry of Agriculture and Natural Resources, 1994).

2.4 Summary of Review

The review shows that though the world’s arable land resources are finite and coming under

increasing pressure from a growing world population and land degradation, intensification of

agriculture will be necessary to feed the earth’s growing population. However since the onset of

agriculture, stream banks have been continually degraded. In view of this stream banks are

regarded as unsuitable areas for cultivation though a contrary view fails to relate stream bank

cultivation to the erosion observed along the banks.

Supporting the earlier view the review reveals that availability of water makes stream banks

attractive and as such vulnerable to over use. This has necessitated legislation on the protection

of the stream banks and the review shows that these vary depending on soils and topography.

Though most legislation prohibits cultivation within 30 metres of a stream, the review shows that

enforcement of such legislation in Southern Africa has not been successful.

Soil erosion by water is highlighted as the major cause of land degradation and ranking high in

tropical climates. However human activity is singled out as a multiplier of soil erosion despite



the fact that soil type influences the processes. It has been shown that stream banks that are not

protected by vegetation become vulnerable to erosion processes thereby contributing to sediment

load in streams. This is therefore depicted as a manifestation of poor land use practices. The

review further shows that soil physical and chemical properties can be used to indicate severity

of soil erosion. Fine textured soils, high bulk density, low organic matter and low pH indicate

severe erosion. High cation exchange capacity shows high clay content and therefore less

erosion.

Finally the review indicates that use of appropriate conservation measures is fundamental to land

improvement though it has been shown that current soil conservation measures fail to cater for

increasing populations. Noteworthy, adoption levels for Malawian smallholder farmers are low

suggesting that the farmers have not clearly understood the detriments of misusing their lands

leading to increased sediment yields from the catchments.



CHAPTER 3: STUDY AREA

This chapter presents the background information about the study area, including the location,

climate, water and land resources, soils and land use.

3.1 Location

The study was carried out in Dedza a district in Central Malawi which lies 74 Km south east of

Lilongwe, the Capital City of Malawi. The district covers an area of 3,624 Km.² and has a

population of 486,682 (1998 Population Census). The study area falls within Nadzipulu

catchment which is part of the Southwest Lakeshore River Basins (Water Resource Area 3)

covering 4958 Km2. Nadzipulu and other streams cover 796 Km

2 (Department of Water,

Ministry of Works and Supplies, 1986). Namanolo and Mwachakula are subcatchments of

Nadzipulu catchment. Both stream catchments lie between Longitudes 0643000 and 0647000

and Latitudes 8410000 and 8414000.

Namanolo Stream is located in Kankhudza Village, Traditional Authority (T/A) Kasumbu and

originates from Dedza Mountain and runs for 3 Km before joining the Mwachakula Stream. The

stream runs adjacent to Dedza Mountain, a protected area, for 2.5 Kilometres. Mwachakula,

originates from Dedza township and runs through Kankhudza and Katsekaminga Villages.

Katsekaminga is under T/A Kamenyagwaza. Wiyo (2007) reports that, the area lies in the

physiographical region of rift valley escarpment. In Malawi, the East African Rift Valley

descends from the plateaux in a series of stepped faults, known collectively as the Rift Valley

Escarpment. The Rift Valley escarpment zone has often precipitous slopes. It is highly dissected

with lots of river valleys where dimba (stream bank) cultivation takes place. The mean altitude

above sea level is between 900 to 1300m.

Dedza

Figure 3.1 Location of Dedza District



Namanolo

Mw

ach

aku

la

643000

643000

644000

644000

645000

645000

646000

646000

647000

647000

648000

648000

8410000

8410000

8411000

8411000

8412000

8412000

8413000

8413000

Dedza mt.shp

Roads.shpMwachakula stream branch.shpMwachakula stream.shpNamanolo stream.shpN

1000 0 1000 2000 3000 Meters

Figure 3.2 Location of Mwachakula and Namanolo Streams in Dedza District



3.2 Rainfall

Dedza, like most of the country experiences uni-modal rainfall that starts from mid or end

November up to early April or end May (Kasomekera, 1992). The average annual rainfall for

Dedza is 1089mm, way above the mean annual rainfall for Water Resource Area 3, which is

851mm with a runoff of 169mm (Department of Water, Ministry of Works and Supplies, 1986).

The rainfall intensity-duration values for different return periods are presented in Table 3.1.

Table 3.1: Rainfall intensity duration for Central Lakeshore Plains and Escarpment

Return

period

(yrs)

Rainfall Intensity (mmh-1) for duration of

15 min 30 min 60 min 3 hrs 6 hrs 24 hrs

2 108.8 85.2 61.3 26.2 15.2 5.4

5 122.0 102.2 74.0 34.4 20.9 7.9

10 129.2 113.2 81.6 39.6 24.7 9.7

25 137.6 126.4 90.6 46.1 29.6 12.0

50 143.2 135.6 97.3 50.9 33.2 13.7

100 148.4 144.6 103.9 55.6 36.9 15.5

Source: Department of Irrigation (1999). Derived by Shela (1990)

Table 3.2 shows rainfall data collected from Dedza RTC, a station within 5 Km of the study area.

The rainfall records for 2007/2008 only cover the period from October 2007 to March, 2008

which was the end of the study period.

Table 3.2: Rainfall amounts for Dedza RTC

YEAR

RAINFALL AMOUNT (mm/month)

Sept Oct Nov Dec Jan Feb Mar Apr May June Total

1987/88 0 19 9 142 301 258 186 18 8 0 942

1994/95 0 21 60 90 339 202 57 5 4 3 779

1995/96 0 0 39 152 157 259 336 47 25 0 1014

1997/98 0 81 81 374 13 178 157 58 2 0 943

2000/01 0 39 108 180 277 308 190 2 16 0 1120

2001/02 0 0 34 185 183 330 134 16 13 4 898

2004/05 0 20 101 283 200 158 33 0 0 0 795

2005/06 14 0 41 208 182 196 252 30 0 0 922

2007/08 0 4 18 240 470 159 119 1010

Average 2 20 54 206 236 227 163 22 8 1 936



Table 3.3: Average Rainfall and number of rainfall events covering study period

Year

Total Rainfall up

to March (mm)

Number of

Events up to

March

Average Rainfall

up to March (mm)

1987/88 916 54 18

1994/95 767 55 14

1995/96 942 76 12

1997/98 883 59 18

2000/01 1102 81 14

2001/02 866 64 14

2004/05 795 66 12

2005/06 892 68 13

2007/08 1010 63 16

3.3 Water and Land Resources

Malawi has a total geographical area of 118,484 Km2 out of which land is 94,276 Km

2 and lakes

are 24,208 Km2. Malawi is rich in surface water resources with rivers draining to Lake Malawi

covering an area of 64,364 Km2, and those draining into Shire and other river basins covering

29,912 Km2. Rivers in Dedza are part of Lakeshore Rivers and on top of being perennial have

catchments with high annual rainfalls (Department of Water, Ministry of Works and Supplies,

1986).

Malawi’s land area has a mean annual runoff of 19 x 109 m

3. The drainage system has been

divided into 17 water resource areas (WRA). Each water resource area is one river basin or in

some cases a number of small river basins. (Department of Water, Ministry of Works and

Supplies, 1986).

Land scarcity is an issue of pressing importance for Malawi (Saka, Green, and Ng’ong’ola,

1995). 16 % of cultivation is taking place in marginal and unsuitable areas (Environmental

Affairs Department, 2002). Rapid population growth is one of the factors blamed for land

degradation as it has exerted much pressure on the agricultural land. In a bid to absorb

population pressure cultivation is extended to marginal areas. Land fragmentation and cultivation

of marginal areas is thus connected to the problem of land degradation in Malawi (Nakhumwa,

2004).

3.4 Soils

Dedza hills have areas of deep soils suitable for agriculture. (Saka, Green, and Ng’ong’ola,

1995). The dominant soils in the area are Bembeke Series occurring along Dedza Hills in

association with Dedza Series. The soil series occurs frequently in densely populated and over

cultivated areas and the profile is often truncated by erosion. The top soil is a sandy clay loam or



occasionally sandy clay with a distinctly yellowish red appearance especially in the truncated

profile (Brown and Young, 1962). The soils within the Dedza Escarpment are characterized as

acidic and of low cation exchange capacity as depicted in Table 3.4.

Table 3.4 Soils of Dedza Escarpment

Agricultural

Ecological

Zone

FAO Soil

Classification

Soil Depth Particle Size pH CEC

Dedza &

Ntcheu

Escarpment

Eutric,

Chromic,

Cambisols

50 – 100cm 0 – 30cm 5.5 – 6.5 5 – 10

(Low)

Source: Nakhumwa (2004)

World Bank (1992) as cited in Environmental Affairs Department (2002) estimated the erosion

level for Dedza as 22 tonnes per ha per year.

3.5 Land Use

The main form of land use in the Lake Malawi Basin is rural subsistence farming. The dominant

factor with regard to land use is the large population of the country that is virtually packed on a

relatively small area of land. Traditional irrigation systems are widespread and make up a

considerable irrigation capacity when added together (SADC-ELMS and WSCU, 2000).

Dedza, due to presence of perennial streams, is generally known for vegetable production which

happens to be a key source of livelihood. In Traditional Authority Kamenyagwaza this takes

place in the bottom river valleys where water tables are shallow and soils fertile (Wiyo, 2007).



CHAPTER 4: MATERIALS AND METHODS

4.1 Introduction

This chapter describes the methods used to determine number of gardens as a surrogate for

stream bank cultivation and distance away from stream, area under cultivation over time,

changes in soil surface levels and extent of gulley erosion. Data were collected between January

and March 2008. Data collected included geographical coordinates for stream bank gardens and

the centre of the streams, aerial photographs and satellite images, measurements for soil surface

changes and gulley sizes, soils and rainfall data and socio economic data including irrigation

technologies and conservation measures used. The soils, rainfall and socio economic data were

used to explain the main variables under study.

Differences along the stream banks are evident for the two streams. Table 4.1 presents a

description of the stream banks from upstream to downstream.

Table 4.1: Description of stream segments based on stream morphology

Stream Segment Condition

Namanolo

Upstream

1 Narrow stream with shallow banks, passing through protected

area. Some gardens waterlogged.

2 Deep stream banks. Stream widens. Reeds evident along

banks.

Namanolo

Downstream

3 Shallow banks with growth of reeds in stream channel.

Unspecified channels due to diversion. Some gardens

waterlogged.

4 Banks deep and rocky. Right bank has steeper slopes.

Mwachakula

Upstream

1 Wide stream with deep sandy banks. Evidence of collapsing

banks.

2 Wide stream and shallow banks with growth of reeds in

stream channel. Some sand mining taking place. Gardens are

waterlogged.

Mwachakula

Downstream

3 Deep stream banks. Some sand mining taking place.

Nsondozi and Mchisu trees growing along stream banks with

evidence of stable banks.

4 Banks deep and steep and stream rocky.

4.2 Data Collection

4.2.1 Determination of distance of gardens from stream

The geographical positions for the centre of the streams and gardens along the streams



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1

2

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6

89

10

13

14

16

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25

23

26

29

20

22

Namanolo

Mw

ach

aku

la

644000

644000

644500

644500

645000

645000

645500

645500

646000

646000

646500

646500

8410000

8410000

8410500

8410500

8411000

8411000

8411500

8411500

8412000

8412000

8412500

8412500

%U Gardens.shpÿ Gullies.shp

Mwachakula stream branch.shpMwachakula stream.shpNamanolo stream.shp

# Soil deposition sites.shpN

700 0 700 1400 Meters

Figure 4.1: Study design showing streams, gardens, gullies and plots for soil surface level

changes determination along Mwachakula and Namanolo streams



were determined using a geographical positioning system (GPS). The global positioning system

(GPS) has become progressively less expensive, lighter and easier to use and the

accuracy of GPS has been improved (Wu and Cheng, 2005).This was a ground truthing exercise

to cater for changes that may have occurred due to the streams changing their course over time.

The centre of Namanolo was marked from source to outlet where it meets Mwachakula and

covered a length of 3199m. Starting from the confluence of Namanolo and Mwachakula and

going upstream of Mwachakula, the stream centre was marked for a length of 3178m.

Geographical positions for 90 stream bank gardens were recorded for both Mwachakula and

Namanolo streams, with 41 gardens along the former and 49 along the latter. Distance of each

garden from the stream was calculated using overlay operations in a Geographical Information

System (GIS). Overlay operations form the core of GIS and deal with the combination of several

maps thus giving new information that was not present in the individual maps (Murwira, 2007).

Where garden edges did not coincide with the stream bank edges, distance between the garden

edge and the stream bank edge was measured to determine the buffer widths.

In addition cultivation patterns within the selected gardens were observed and these included use

of soil conservation measures and irrigation technologies used. Records from Bembeke

Agricultural Extension Planning Area (EPA) and Dedza Irrigation Office were used to validate

the observed patterns. This data was collected to understand extent of cultivation in terms of

distance of gardens from the stream.

4.2.2 Determining extent of stream bank cultivation over time

Three aerial photographs covering the study area for the years 1980, 1982 and 1995 were

acquired, scanned and geo-referenced. In addition a SPOT image for 2002 was also acquired.

This selection was based on availability of the photos and images. Gardens within 50 metres of

the streams were digitized for the sake of comparability since from field observation it had been

established that stream bank gardens were located within that distance. Total area under

cultivation along each stream and for each of the selected years was determined using GIS

4.2.3 Determination of changes in soil surface levels

A reconnaissance method by the name pin erosion method was used to determine changes in soil

surface levels. Reconnaissance methods are ways to get a first approximation of the amount of

erosion in a given situation - this approximation may be all that is needed, or it could be followed

by more precise studies if required. The main advantage of reconnaissance methods is that,

because they are cheap and simple, many measurements can be made and so the results can be

reliable and representative - which means they are believable and usable - more so than a single

precise measurement at a site which may not be representative (Hudson, 1993).

Sites from where changes in soil surface levels would be measured were selected along each

stream based on evidence of soil erosion as observed during reconnaissance survey. A total of 21

sites were selected along bank edges of the streams and geographical coordinates for each site



taken. These included 11 sites along Mwachakula and 10 sites along Namanolo. The sizes of the

sites ranged from 2.5 to 5.0m2.

At the edges of the stream banks a total of 194 stakes were driven into the ground at 0.5m

intervals so that the top of the stake gave a datum from which changes in the soil surface level

could be measured. To eliminate effects of sand mining evident in Mwachakula stream, no stakes

were placed on the stream bed. The number of stakes per site ranged from 4 to 18 depending on

the size of the site. The exposed part of the stake was measured at the beginning of the study in

January 2008 to determine the base line and also at the end of the study in March 2008 to

determine the depth of soil deposition or removal. According to Haigh (1977) quoted in Hudson

(1993) the amount of stake exposed due to erosion or covered due to deposition is the amount of

change at the stream bank erosion site between times of observation. The second measurement

was made from 96 stakes in 14 sites after 98 stakes were washed away due to unexpected high

stream levels.

4.2.4 Determination of gulley occurrence

The method included determination of the number of gullies and their sizes. For studies on

gulley erosion Hudson (1993) recommends that measurements for the horizontal spread as well

as the vertical changes within the gulley be recorded. A total of 20 gullies were identified and

their geographical positions recorded. The gullies were overlaid on the stream catchments and

number of gullies recorded for a stretch of 200m along each of the 8 stream segments. The length

of the stretch was determined based on field observations. For each gulley measurements were

recorded for length, width and depth from which gulley volumes were calculated (Stocking, M.

and Murnaghan, N., 2000).

In addition some factors contributing to soil erodibility were investigated. 25 soil sampling sites

were identified along the streams. These included areas surrounding nineteen gullies and six soil

deposition sites situated along the edges of the streams. The soils were sampled to a depth of one

metre covering 0 – 20cm, 20 – 40cm, 40 – 60cm, 60 – 80cm and 80 – 100cm depths. However,

in sites where the water table was high, sampling could not be done up to the one metre depth.

From each site three to five sub samples were collected to form one composite sample.

The soils were then analysed for soil texture, pH, organic matter, bulk density and cation

exchange capacity using standard laboratory techniques which included the hydrometer method,

pH meter, titration method, core method and flame photometer, respectively (Bvumbwe

Chemistry Laboratory Manual, Undated).

4.2.5 Determination of relationship between extent of cultivation and extent of erosion indicators

The relationship between extent of cultivation and extent of soil erosion indicators was

determined through graphical, non linear regression and correlation analyses.



4.3 Data Analysis

A test of data for normality using one-sample Kolmogorov – Smirnov Test in SPSS 13.0 showed

that data did not follow a normal distribution therefore non parametric statistics were used to test

for significance. Relationships were therefore analysed using Spearman correlation coefficient

and non linear regression analyses and the differences compared using the Mann-Whitney U test.



CHAPTER 5: RESULTS AND DISCUSSIONS

This chapter presents the findings from the study whose main objective was to determine the

relationship between stream bank cultivation and soil erosion indicators. Results and analyses are

presented per objective in four sections and a summary of discussions given in the fifth. The first

two sections present results and analyses using number of gardens and area under cultivation as a

surrogate for the extent of stream bank cultivation, followed by a section on change in soil

surface levels and gulley occurrence highlighted as the extent of erosion indicators and the fourth

section presents analyses on the relationship between stream bank cultivation and the erosion

indicators.

5.1 Relationship between number of gardens and distance from the stream

In this study it was hypothesised that there is no significant relationship between number of

gardens and distance away from the stream.

Mwachakula: P = 0.0001 Namanolo: P = 0.0000

Figure 5.1: Relationship between number of gardens and distance away from stream

0 5 10 15 20 25 30

Distance from stream (m)

-1

1

3

5

7 Mwachakula

Namanolo

Nu

mb

er o

f g

ard

en

s

5.716 - 1.68*ln x

3.29 - 0.8321*ln x



Figure 5.1 illustrates the significant (α=0.05) relationship between number of gardens and

distance away from the stream. It can be observed that there is a consistent negative relationship

between number of gardens and distance from stream for both Mwachakula and Namanolo

streams. It can also be observed that the relationship along Namanolo is represented by a steeper

gradient than that for Mwachakula between 0 and 18 metres from the stream.

This indicates that there are more gardens closer to the stream than there are further from the

stream. It also indicates that smallholder farmers along Mwachakula and Namanolo concentrate

their cultivation within 18 metres of the stream. This is consistent with Vigiak et.al., (2008) who

observed that many subsistence and income-generating activities that are integral parts of rural

household economies are undertaken in riparian zones. This is further supported by (Matiza,

1992) who reported that the legislation on stream bank protection is not being enforced. As Bell

and Hotchkiss (1991) observed, in some areas cultivable land lies close to the water courses so

that on the basis of technically objective measurement, no land would be available for cultivation

outside the 30m limit. The study also revealed that 52% of the gardens along the two streams do

not have any buffer areas between their edges and the stream (Appendix 1 Table 7.3). For

gardens with buffers the mean width observed was 3.7±6 metres (Appendix 1 Figure 7.1). This

implies that cultivation is done right to the edge of the stream bank and on the stream bed in

some cases. This is supported by Zidana (2008) who observed that some smallholder farmers

along Linthipe and Lilongwe Rivers cultivate even on the stream bed. The steeper gradient for

Namanolo indicates that for any distance within 18 metres from the stream there are more

gardens for Namanolo than for Mwachakula.

Based on Figure 5.1 the inflexion point formed by the natural logarithmic functions was taken to

define a threshold of 18 metres. Figure 5.2 illustrates the relationship between distances

classified into less than and more than 18 metres and number of gardens to further support the

relationship already illustrated in Figure 5.1.

Results show that there are significant (α = 0.05) differences between number of gardens within

18 metres and those beyond. This confirms that there are more gardens within 18 metres of the

stream along both Mwachakula and Namanolo streams. This is supported by a study carried out

by Wiyo (2007) that revealed that cultivation along stream banks was a key source of livelihood

for the area under Traditional Authority Kamenyagwaza and contributed over 60 % of the

household incomes.

Based on the observed gradients for the natural logarithmic functions before the inflexion point

in Figure 5.1, Figure 5.3 illustrates that there are no significant (α = 0.05) differences in

cultivation distances along Mwachakula and Namanolo streams.

Considering the fact that part of Namanolo runs adjacent to a protected area, one would expect

less cultivation along this stream. This could indicate encroachment of farmers into the protected

area and could be explained by the fact that, increase in population pressure is forcing people to

cultivate in areas that would not normally be cultivated (Nyirongo, 2001).

It was further observed that farmers along the two streams practiced irrigation farming using

temporary stream diversions and watering cans (Appendix 1 Table 7.1). Based on the observed



threshold of 18 metres Figure 5.4 illustrates significant (α = 0.05) differences between number of

gardens under irrigation and those under rain-fed farming only.

This indicates that within 18 metres of the stream there are more gardens under irrigation than

those that are only rain-fed. This could suggest that irrigation is one of the factors that are

influencing location of gardens along the streams. Kadyampakeni (2004) reports that farmers use

stream banks in order to spread risk of crop failure arising from vagaries of nature and other

hazards. With the erratic rains being experienced by almost the whole SADC, Malawi has raised

a call for reduced dependence on rain-fed agriculture only and smallholder farmers have

responded. Stream banks have become areas of highest value for Malawi because water can be

accessed year-round (Peters, 2004).

Figure 5.2: Comparison between number of gardens based on a threshold of 18 metres

Furthermore the study observed that some farmers along the two streams used conservation

measures including elephant grass, bamboo and sugarcane (Appendix 1 Table 7.2). Again based

More than 18m from stream Less than 18m from stream

6

5

4

3

2

1

Nu

mb

er o

f g

ard

en

s

20

P = 0.005



on the observed threshold of 18 metres Figure 5.5 illustrates significant (α = 0.05) differences

between number of gardens with soil conservation measures and those without.

This indicates that within 18 metres of the streams there are more gardens without conservation

measures than there are gardens with conservation measures. This finding is consistent with the

results from studies by Mangisoni (1999) and Kumwenda (1995) reported in Nakhumwa (2004)

that adoption levels for soil conservation measures were low among Malawian smallholder

farmers.

Figure 5.3: Number of gardens along Mwachakula and Namanolo streams

Namanolo Mwachakula

6

5

4

3

2

1

0

Nu

mb

er o

f g

ard

en

s

P = 0.292



Figure 5.4: Number of gardens with and without irrigation within 18 metres of the stream

This study reveals that there is a negative relationship between number of gardens and distance

away from the stream along Mwachakula and Namanolo streams. In addition cultivation is

concentrated within 18 metres of the streams with garden boundaries on the edge of the stream

banks or even right on the stream bed in some cases, with no form of soil conservation measures

and under irrigation using watering cans.

5.2 Change in extent of area under cultivation over time

The study hypothesized that there is no significant change in the extent of area under stream

bank cultivation along Mwachakula and Namanolo streams over time. Figure 5.6 illustrates the

distribution of cultivated area along Mwachakula and Namanolo between 1980 and 2002.

Figures 5.7 and 5.8 illustrate the change in area under cultivation over the 22 years.

No Irrigation Irrigation

5

4

3

2

1

0

Nu

mb

er o

f g

ard

ens

wit

hin

18

m

P = 0.002



Figure 5.5: Number of gardens with and without conservation within 18 metres of the stream

It can be observed from Figures 5.7 and 5.8 that total area under cultivation increased between

1980 and 1982, remained constant between 1982 and 1995 and then decreased between 1995 and

2002. Noteworthy the highest area under cultivation can be observed between 1982 and 1995. It

can further be observed that a similar trend is displayed for Mwachakula (M) and Namanolo (N)

though the decrease for Namanolo starts in 1982. Furthermore it can be observed that for each of

the years area under cultivation along Namanolo is more than that along Mwachakula.

This indicates that area under cultivation has been changing over time along the two streams.

The fact that the highest area observed is between 1982 and 1995 is supported by Saka, Green,

and Ng’ong’ola (1995) who found that droughts experienced in 1991/92 rekindled interest in

irrigated agriculture among Malawian smallholder farmers. This could imply that by 1995 the

smallholder farmers had responded to the calls for increased irrigated agriculture.

Without conservation With conservation

12

10

8

6

4

2

0

Nu

mb

er o

f g

ard

ens

wit

hin

18

m

P = 0.000



Namanolo80.shpMwachakula80.shpMwachakulab80.shp1980 gardens.shp

800 0 800 1600 Meters

N

800 0 800 1600 Meters

Namanolo82.shpMwachakula82.shpMwachakulab82.shp1982r gardens.shp

N

Area under cultivation in 1980 Area under cultivation in 1982

1000 0 1000 2000 Meters

Mwachakula 1995.shpNamanolo 1995.shpMwachakula branch 1995.shp1995 gardens.shpN

900 0 900 1800 Me te rs

M wa ch akula 02.shpM wa ch akula b02.shpN am an olo02.shp2002 gardens .shp

N

Area under cultivation in 1995 Area under cultivation in 2002

Figure 5.6: Area under cultivation along Mwachakula and Namanolo from 1980 to 2002



Key: M Mwachakula N Namanolo T Total Area

Figure 5.7: Total area under cultivation between 1980 and 2002

Key: M Mwachakula N Namanolo

Figure 5.8: Proportions for area under stream bank cultivation over time

However the decrease in area under cultivation between 1995 and 2002 contradicts a report by

the Environmental Affairs Department (2002) that reveals that smallholder irrigation

development in Malawi has quadrupled over the past four decades in terms of land area brought

under irrigation. One possible explanation for the decreasing trend could be lower than average

2002 1995 1982 1980

T N M T N M T N M T N M

14

12

10

8

6

4

2

0

Are

a u

nd

er c

ult

iva

tio

n (

Ha

)

2002 1995 1982 1980

N M N M N M N M

0.4

0.3

0.2

0.1

0.0 Are

a u

nd

er c

ult

ivati

on

(H

a)

Error bars: 95.00% CI



rainfall amounts in the season 2001/2002 (Table 3.3) which could have led to lower flows in the

streams. The other possible explanation could be associated with soil degradation along the

stream banks. There is evidence of banks collapsing especially along Mwachakula and fields

reducing in size due to large chunks of land collapsing into the stream (See Appendix 2 Figure

7.2).

Based on the observations made from Figures 5.7 and 5.8 on differences between cultivated

areas over the years, Figure 5.9 illustrates that there are no significant (α=0.05) differences

between Mwachakula and Namanolo over time. This indicates that over the 22 years the change

in area under cultivation along the two streams has followed a similar trend.

Figure 5.9: Extent of cultivation along Mwachakula and Namanolo streams over time

5.3 Extent of Soil Erosion Indicators

5.3.1 Changes in soil surface levels

The study also hypothesized that there is no significant difference in the changes in soil surface

levels along Mwachakula and Namanolo. Figure 5.10 and 5.11 illustrate that both positive and

negative changes in soil surface levels occurred. It can be observed that there is more variation in

soil deposition 82.86±104.738 (n = 70) than there is in soil loss 60.96±69.857 (n = 20). This

indicates that change in soil surface levels is more in the positive direction than it is in the

negative.

However Figures 5.12 and 5.13 illustrate that there are no (α=0.05) significant differences in

both soil deposition and loss between Mwachakula and Namanolo streams. This indicates that

there is as much soil deposition and soil loss along Mwachakula as there is along Namanolo

stream. Analysis of soils of the area reveals that there are significant (α=0.05) differences in soil

textural classes and organic matter content between the two streams (Appendix 3 Tables 7.5 and

Namanolo Mwachakula

0.4

0.3

0.2

0.1

0.0 Are

a u

nd

er

cu

ltiv

ati

on

(9

5%

CI)

P = 0.686



7.7). However further analysis shows that there is no significant (α=0.05) relationship between

soil loss or deposition and the two soil properties within the 40cm soil depth (Appendix 3 Tables

7.10 to 7.13). The susceptibility of any soil type to erosion depends upon the physical and

chemical characteristics of the soil, in addition to its protective vegetative cover, topographic

position (slope length and gradient), the intensity of rainfall, and the velocity of runoff water

(McCombs, 2007).Therefore soil deposition and loss along the two streams could be related to

other factors affecting soil erodibility other than the soil physical properties.

Based on field observations it is evident that the stream morphologies are different between

upstream and downstream sections for both Mwachakula and Namanolo (Table 4.1). These

differences are illustrated in Figures 5.14 and 5.15 for Mwachakula and Figures 5.18 and 5.19

for Namanolo. It can be observed that downstream Mwachakula is rocky and the banks are

vegetated and that upstream cultivation is up to the edge of the stream and the banks are bare.

Figure 5.16 illustrates that there are no significant (α=0.05) differences in soil loss however

Figure 5.17 illustrates significant (α=0.05) differences in soil deposition, between Mwachakula

upstream and downstream sections.

This indicates that there is more soil deposition upstream than downstream of Mwachakula. This

could be related to the differences in stream morphologies upstream and downstream. However

Figure 5.18 and 5.19 illustrate that there are no significant (α=0.05) differences in both soil loss

and soil deposition along Namanolo stream. This indicates that there is as much soil loss and soil

deposition upstream and downstream of Namanolo. This could similarly be due to the fact that

there is no relationship between the soil texture and the erosion processes occurring.

5.3.2 Gulley count

The study also hypothesized that there is no significant difference in the number of gullies

occurring along Mwachakula and Namanolo streams. Figure 5.20 illustrates that there are no

significant (α=0.05) differences in the number of gullies found along the two streams.

This indicates that despite the apparent differences in the stream morphologies there is no

difference in the number of gullies found along the two streams. Since occurrence of gullies is

considered a visible manifestation of poor land use practices (Armour and Russell, 1997) the

results could imply that land use practices along the two streams are similar.

5.3.3 Gulley Volume

It was further hypothesized in the study that there are no significant differences in the gulley

volumes occurring along Mwachakula and Namanolo streams. Figure 5.21 illustrates the

distribution of gulley volumes along Mwachakula and Namanolo streams. It can be observed that

the most occurring gulley volumes are between 0 and 10m3 for both Mwachakula and Namanolo

streams. It can also be observed that there is a wide variation of gulley volumes 9.85 ± 14.3 m3

(n =20).



Figure 5.10: Soil deposition along Mwachakula and Namanolo Figure 5.11: Soil loss along Mwachakula and Namanolo

Figure 5.12: Comparison of soil deposition Figure 5.13: Comparison of soil loss

500 400 300 200 100 0

Soil deposition (mm)

40

30

20

10

0

Fre

qu

ency

Mean = 82.86 Std. Dev. = 104.738 N = 70

Namanolo Mwachakula

300

250

200

150

100

50

0 S

oil

lo

ss (

mm

)

4 2

1 P = 0.959

300 250 200 150 100 50 0

Soil loss (mm)

15

12

9

6

3

0

Fre

qu

ency

Mean = 60.96 Std. Dev. = 69.857 N = 26

Namanolo Mwachakula

500

400

300

200

100

0

So

il d

epo

siti

on

(m

m)

69

68 P = 0.990



Figure 5.14: Mwachakula downstream

Figure 5.15: Mwachakula upstream



Figure 5.16 Upstream downstream soil loss Figure 5.17 Upstream downstream soil deposition

Figure 5.18: Upstream downstream soil loss Figure 5.19 Upstream downstream soil deposition

Downstream Upstream

Mwachakula

300

250

200

150

100

50

0

So

il L

oss

(m

m)

1 P = 0.075

Downstream Upstream

Mwachakula

500

400

300

200

100

0

So

il D

epo

siti

on

(m

m)

39

38

P = 0.025

Downstream Upstream

Namanolo

150

100

50

0

So

il L

oss

(m

m)

P = 0.056

Downstream Upstream

Namanolo

250

200

150

100

50

0 S

oil

Dep

osi

tio

n (

mm

) 29

P = 0.359



Figure 5.20: Number of gullies along 200m stretches of different stream segments

Figure 5.21: Gulley volumes along Mwachakula and Namanolo streams

This indicates that there are more gullies with volumes less than 10m3 than those with volumes

above 10m3. Based on this observation the gullies were grouped into classes of less than and

more than 10m3. Figure 5.22 and 5.23 illustrate classified gulley volumes into less than and more

than 10m3. Results show that there are no significant (α=0.05) differences between gulley

volumes of both classes for Mwachakula and Namanolo streams. This indicates that the extent of

gulley erosion along Mwachakula is similar to that along Namanolo stream implying that there

are no differences in soils lost through gulley erosion along the two streams.

Mean = 9.85

70 60 50 40 30 20 10 0

Gulley Volume (m3)

20

15

10

5

0

Fre

qu

ency

Mean = 9.85

Std. Dev. = 14.3

N = 20

Namanolo Mwachakula

4

3

2

1

0

No

. o

f g

ull

ies

per

200

m

P = 0.486



Analysis of soils along Mwachakula and Namanolo revealed that there are no (α=0.05)

significant differences in bulk densities, pH and cation exchange capacity but there are (α=0.05)

significant differences in soil textural classes and organic matter content (Appendix 3 Tables 7.5

to 7.9). Bulk density and pH are some of the characteristics indicative of soil erosion. Both

increase with severity of soil erosion (Mokma and Sietz, 1992). The fact that there are no

differences in these soil properties could explain the similarities in the gulley volumes along the

two streams. On the other hand though there are differences in organic matter content these

differences may not be reflected in gulley volumes because the range of organic matter content

(0.98 to 3.6 %) shows that all the soils are already vulnerable to erosion. According to Ternan,

Williams, and Tanago, (1994) soils with less than 3.5% organic matter are most vulnerable to

erosion because of the lack of organic polymers or binding agents.

The findings from this study reveal that there are no significant (α=0.05) differences in the extent

of soil erosion indicators along the two streams. The changes in soil surface levels show more

soil deposition than soil loss however with no differences between the two streams. Nevertheless

along Mwachakula there is more soil deposition occurring upstream than downstream. However

in terms of gulley occurrence there are no differences along the two streams.

5.4 Relationship between Extent of Cultivation and Soil Erosion Indicators

5.4.1 Relationship between number of gardens and changes in soil surface level

It was hypothesized that there is no significant relationship between number of gardens and the

changes in soil surface levels. Figures 5.24 and 5.25 illustrate the relationship between number

of gardens and soil loss and soil deposition, respectively. It can be observed that there is a

negative relationship between number of gardens and soil loss and a positive relationship

between number of gardens and soil deposition. It can also be observed that soil loss and

deposition can be related to number of gardens based on groupings of the gardens that can be

observed from Figures 5.24 and 5.25.

The indication is that soil loss is decreasing with an increase in number of gardens and that soil

deposition is increasing with increase in number of gardens. The relationship between soil loss

and number of gardens would not normally be expected however this relationship could arise

from the fact that the sample of stakes may not have been representative. Out of 96

measurements made only 26 registered soil loss.

Figures 5.26 and 5.27 illustrate the relationship between the soil erosion processes and number of

gardens based on the groupings of below 10 gardens and above 10 gardens to further illustrate

the relationship in Figures 5.24 and 5.25. Figure 5.26 illustrates that there is no significant

(α=0.05) relationship between number of gardens and soil loss however Figure 5.27 illustrates a

significant (α=0.05) relationship between number of gardens and soil deposition.

This indicates that there is more soil deposition occurring where there are more than 10 gardens

than where there are less than 10 gardens. Previous discussions highlighted that most of the

gardens are located within 18 metres of the stream and that 52% of the gardens had no buffer

zones and where buffer zones were present the widest buffer was 9.7 metres.



Figure 5.22 Gulley volumes less than 10m3 Figure 5.23 Gulley volumes more than 10m

3

Namanolo Mwachakula

0.8

0.6

0.4

0.2

0.0 G

ull

ey v

olu

mes

more

th

an

10m

3

P = 0.686

Namanolo Mwachakula

2.0

1.5

1.0

0.5

0.0

Gu

lley

volu

mes

les

s th

an

10m

3

29

28

P = 0.371



Figure 5.24: Number of gardens and soil loss Figure 5.25: Number of gardens and soil deposition

18 16 14 12 10 8 6

Number of gardens

300

250

200

150

100

50

0

Soil

loss

(m

m)

18 16 14 12 10 8 6

Number of gardens

500

400

300

200

100

0

Soil

dep

osi

tion

(m

m)



The results therefore further indicate that most of the soil deposition is occurring where gardens

are located within 18 metres of the stream and mostly without any buffer zones. This finding is

supported by Vanderwel and Jedrych (2005) who showed that there was less sediment leaving

watersheds which had buffer zones when compared to those which had no buffer zones. This

confirms that the closer gardens are located to the stream the more soil will deposit along the

bank edges.

Figure 5.26: Soil loss/ threshold of 10 gardens Figure 5.27: Soil deposition/threshold of 10 gardens

Furthermore previous discussions revealed that within 18 metres of the stream most of the

gardens are under irrigation. Figures 5.28 and 5.29 illustrate the relationship between soil

deposition and number of gardens under irrigation and under rain-fed cultivation, respectively

within 18 metres of the stream.

It can be observed that there is a positive relationship between number of irrigated gardens and

soil deposition and a negative relationship between number of rain-fed gardens and soil

deposition. It can also be observed that soil deposition can be related to groupings of less than 6

gardens and more than 6 gardens. Figures 5.30 and 5.31 illustrate significant (α=0.05)

differences between soil deposition from less than 6 gardens and that from more than 6 gardens.

This indicates that for gardens under irrigation there is more soil deposition coming from

sections with more than 6 gardens than there is from sections with less than 6 gardens. However

for gardens that are only rain-fed there is more deposition where there are less than 6 gardens

than where there are more than 6 gardens. This further confirms that the soil deposition occurring

where gardens are located within 18 metres of the stream is mostly occurring due to irrigation.

This is consistent with the Malawi State of Environment Report which states that because most

of the land under irrigation is along the river banks, increase in irrigated land area has increased

the sediment load in the rivers due to poor agricultural practices (Environmental Affairs

Department, 2002).

gardens gardens More than 10 Less than 10

300

250

200

150

100

50

0

Soil

lo

ss (

mm

)

19

18

1 P = 0.659


500

400

300

200

100

0

Soil

dep

osi

tio

n (

mm

)

62

60

64

P = 0.030



Figure 5.28: Number of irrigated gardens and soil deposition

Figure 5.29: Number of rain-fed gardens and soil deposition

15 12 9 6 3 0

Number of gardens under irrigation

500

400

300

200

100

0

So

il d

epo

siti

on

(m

m)

10 8 6 4 2 0

Number of gardens without irrigation

500

400

300

200

100

0

So

il d

eposi

tion

(m

m)



Figure 5.30: Soil deposition and irrigated gardens Figure 5.31: Soil deposition and rain-fed gardens

Based on previous discussions on soil conservation Figures 5.32 and 5.33 illustrate the

relationship between soil deposition and the number of gardens with and without conservation,

respectively within 18 metres of the stream.

It can be observed that a negative relationship exists between soil deposition and number of

gardens with conservation measures whereas a positive relationship exists between soil

deposition and number of gardens with no conservation measures. It can further be observed that

soil deposition can be related to number of gardens based on classes of less than 3 gardens and

more than 3 gardens.

This indicates that soil deposition will decrease with an increase in number of gardens with

conservation. On the other hand deposition will increase with an increase in number of gardens

without conservation. Figures 5.34 indicates no significant (α = 0.05) differences in soil

deposition regardless of the number of gardens with conservation. This could be due to the type

of conservation measures under use (Appendix 1 Table 7.2). Vigiak, Ribolzi, Pierret, Valentin,

Sengtaheuanghoung and Noble (2008) note that some conservation measures like bamboo may

not be appropriate for soil conservation.

Figure 5.35 illustrates that there are significant (α = 0.05) differences in soil deposition based on

the threshold of 3 gardens without conservation. This indicates that more soil deposition is

expected where there are more gardens without conservation. Out of a total of 77 gardens

without conservation 87 % are within 18 metres of the stream (Appendix 1 Table 7.2). This

further indicates that most contribution to soil deposition emanates from cultivation within 18

metres of the stream and more so from the fact that a higher percentage of these gardens are

without any conservation measures. This is consistent with the Malawi State of Environment


500

400

300

200

100

0

So

il d

epo

siti

on

(m

m)

64

62

P = 0.001


500

400

300

200

100

0

So

il d

ep

osi

tio

n (

mm

)

68

66

69 P = 0.000



Report that some stream catchments are under intensive cultivation often without adequate

conservation measures thereby affecting operation of rural water supply schemes (Environmental

Affairs Department, 2001).

Figure 5.32: Number of conserved gardens and soil deposition

5.4.2 Relationship between number of gardens and gulley volumes

It was further hypothesized that there is no significant relationship between number of gardens

and gulley volumes.

Figures 5.36 illustrates the relationship between number of gardens and gulley volumes less than

10 m3 and Figure 5.37 illustrates a similar relationship with gulley volumes above 10 m

3. It can

be observed that there is a positive relationship between gulley volumes and number of gardens

indicating that gulley volumes increase with increase in number of gardens. It can also be

observed that the gulley volumes can be related to a classification of less than 9 and more than 9

gardens.

Figures 5.38 and 5.39 illustrate that there are no significant (α = 0.05) differences between both

types of gulley volumes and number of gardens. This indicates that gulley sizes along

Mwachakula and Namanolo occur regardless of the extent of cultivation along the stream banks.

This therefore implies that cultivation along these stream banks cannot be related to the gulley

erosion occurring along the banks. Norman and Douglas (1994) suggest that gulley erosion is

considered a problem exported off the farmers’ land. This implies that gullies occurring along

the stream banks could be an indication of land use practices upland of the stream banks.

6 5 4 3 2 1 0

Number of gardens with conservation within 18m

500

400

300

200

100

0

Soil

dep

osi

tio

n (

mm

)



Figure 5.33: Number of un-conserved gardens and soil deposition

Figure 5.34: Soil deposition along conserved gardens

12 10 8 6 4 2 0

Number of gardens without conservation within 18m

500

400

300

200

100

0

So

il d

epo

siti

on

(m

m)

More than 3 gardens Less than 3 gardens

Conservation used

500

400

300

200

100

0

So

il d

epo

siti

on

(m

m)

64

P = 0.129



Figure 5.35: Soil deposition along un-conserved gardens

From previous discussions there is a clear indication that the highest percentage of gardens

within 18 metres of the stream are without any conservation measures. Based on this observation

Figures 5.40 and 5.41 illustrate a relationship between gulley volumes and gardens without

conservation. It can be observed that there is a positive relationship between gulley volumes and

number of gardens without conservation. This indicates that higher gulley volumes are expected

where there are more gardens without conservation for both types of gullies.

Furthermore it can be observed that the gulley volumes can be related to number of gardens

based on a classification of less than 9 and more than 9 gardens without conservation. However

Figures 5.42 and 5.43 illustrate that there are no significant (α = 0.05) differences between both

types of gulley volumes and number of gardens without conservation.

This indicates that gullies along the two streams occur regardless of the number of gardens

without conservation. This further indicates that the gullies occurring along Mwachakula and

Namanolo streams cannot be related to the failure of farmers to conserve their stream bank

gardens. This implies that the gullies are occurring due to factors other than the patterns of

cultivation along the streams.


No conservation Used

500

400

300

200

100

0

Soil

dep

osi

tio

n (

mm

)

69

68

64

P = 0.013



Figure 5.36: Volumes < 10 m3 and number of gardens

Figure 5.37: Volumes >10 m3 and number of gardens

This study reveals that whereas there is a significant (α = 0.05) positive relationship between

number of gardens and soil deposition occurring along the two streams there is no relationship

between number of gardens and gulley volumes. The positive relationship shows that soil

deposition is occurring where there is more cultivation which happens to be within the distance

of 18 metres from the stream. Noteworthy this is where most of the gardens are under irrigation,

with no buffer zones and with no form of soil conservation measures.

18 15 12 9 6 3

Number of gardens

10

8

6

4

2

0

Gu

lley

Volu

me

(m3)

20

14 12 10 8 6 4 2

Number of gardens

70

60

50

40

30

10

Gull

ey V

olu

me

(m3)



Figure 5.38: Gulley volumes based on threshold of 9 gardens Figure 5.39: Gulley volumes based on threshold of 9 gardens


70

60

50

40

30

20

10

Gu

lley

Vo

lum

e (m

3)

P = 0.180


10

8

6

4

2

0

Gu

lley

Vo

lum

e (m

3)

P = 0.386



5.5 Summary of findings and discussions

This study reveals that there is a significant (α = 0.05) negative relationship between number of

gardens and distance away from stream and that cultivation along Mwachakula and Namanolo

streams is concentrated within 18 metres of the streams where cultivation mostly extends to the

edge of the stream bank or even right to the stream bed in some cases. The findings also reveal

that most of the gardens within this distance, and with no form of soil conservation measures, are

under irrigation using watering cans. In addition 52% of the gardens do not have any buffer

zones and for those that have buffers the mean width is 3.7 ± 6 metres. Furthermore the findings

show that area under cultivation along Mwachakula and Namanolo streams has been changing

over time (Appendix 2 Table 7.4). The trend shows an increase between 1980 and 1995 and a

decrease between 1995 and 2002.

The study also reveals that though changes in soil surface levels occurred there was more soil

deposition than soil loss recorded however with no differences between the two streams.

Nevertheless along Mwachakula more soil deposition occurred upstream than downstream.

However in terms of gulley occurrence there are no significant (α = 0.05) differences along the

two streams.

Finally the findings reveal that whereas there is a significant (α = 0.05) positive relationship

between number of gardens and soil deposition occurring along the two streams there is no

relationship between number of gardens and gulley volumes. It is further revealed that most of

the soil deposition is occurring within 18 metres of the stream where most of the gardens are

under irrigation but neither have any buffer zones nor any form of soil conservation measure.

As has been revealed in literature availability of water makes stream banks attractive and as such

vulnerable to over use. Though most legislation prohibits cultivation within 30 metres of a

stream, as observed by Matiki (2005) the regulation is not being enforced in Malawi. Coupled

with land scarcity in the country and promotion of irrigation farming, cultivation along stream

banks is a practice that will remain part of Malawi’s agriculture. As Kamthunzi (2000) reports

smallholder farmers cultivate on areas between 0.1 and 0.4 hectares. In most cases these gardens

lie within 30 metres of the stream and as Bell and Hotchkiss (1991) observe in some cases it

would not be possible to cultivate beyond this limit because the land may not be cultivable.

However based on the findings of this study it shows that cultivation along these stream banks is

contributing to soil deposition along the banks.

As Wiyo (1999) reports research has shown that a major cause of erosion in the SADC is not

surface runoff but raindrop impact. These findings could therefore indicate that the soil

deposition occurring along these banks is due to raindrop impact. This could imply that the banks

are exposed to these impacts due to limited vegetation cover.


University of Zimbabwe – IWRM MSc Thesis Chimango Mlowoka June 2008

50

Figure 5.40: Volumes < 10 m3 and gardens without conservation Figure 5.41: Volumes >10 m

3 and gardens with conservation

14 12 10 8 6 4 2 0

Number of gardens without conservation

10

8

6

4

2

0

Gu

lley

Vo

lum

e (m

3)

14 12 10 8 6 4 2 0

Number of gardens without conservation

70

60

50

40

30

20

10

Gu

lley

Vo

lum

e (m

3)



51

Figure 5.42: Volumes <10m3 based on threshold of 9 gardens Figure 5.43: Volumes >10m

3 based on threshold of 9 gardens


10

8

6

4

2

0

Gu

lley

Vo

lum

e (m

3)

P = 0.386


70

60

50

40

30

20

10 G

ull

ey V

olu

me

(m3)

P = 0.180



52

The study reveals that soil deposition tends to increase with an increase in number of gardens.

With land pressure so high in Malawi and forcing 28% of marginal or unsuitable land into

cultivation (SADC-ELMS and WSCU, 2000) this implies that more area along stream banks is

already under cultivation. What may also amplify the soil deposition problem is the type of crops

grown. The most common crops grown in the area are maize and leafy vegetables. Kasomekera

(1992) observes that the majority of crops grown in Malawi are poor cover crops and this makes

most of the cultivated land vulnerable to erosion by water. Noteworthy 87% of the gardens

within 18 metres of the stream are not conserved in any way. This is supported by (SADC-

ELMS and WSCU, 2000) who report that smallholder farmers within the Zambezi basin do not

practice soil and water conservation technologies, thereby amplifying soil erosion problems. The

fact that most of the gardens are within 18 metres of the stream may not in itself be enough to

contribute to soil deposition along the two streams. What is likely is the synergistic effect of

having gardens that are very close to the stream, under irrigation, without any form of

conservation and not bound by any buffer zones. This is consistent with Anderson and

Thampapillai (1990) who observe that erosion, which finally contributes to sediment load in

streams is a manifestation of poor land use practices.

It has been shown by Nakhumwa (2004) that adoption of soil conservation measures is low

among Malawian smallholder farmers, supporting the findings from this study. One possible

reason for lack of soil conservation may be the issue of land scarcity which forces farmers to

maximize use of their land in a bid to increase crop production. The other reason could be the

use of inappropriate soil conservation measures. It was noted that the most used measure along

Mwachakula was elephant grass (Appendix 1 Table 7.2). However during the study period it was

observed that collapsing banks included those that were planted to the grass (Appendix 4 Figure

7.3). This shows that though some of the farmers use conservation measures, they may not be

appropriate for these stream banks.



53

CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS

6.1 Conclusions

This study concludes that a relationship exists between the extent of stream bank cultivation and

the extent of soil deposition along Mwachakula and Namanolo Streams based on the following

findings:

1. There is a significant (α=0.05) negative relationship between number of gardens and

distance away from the stream along Mwachakula and Namanolo streams indicating that

more gardens are located closer to the streams than further from them. In addition

cultivation is concentrated within 18 metres of the streams with garden boundaries on the

edge of the stream banks or even right on the stream bed in some cases, with no form of

soil conservation measures and under irrigation using watering cans.

2. There is no significant (α=0.05) change in area under cultivation along Mwachakula and

Namanolo streams, however the trend observed shows an increase between 1980 and

1995 and a decrease between 1995 and 2002.

3. There are no significant (α=0.05) differences in the extent of soil erosion indicators

along the two streams. The changes in soil surface levels show more soil deposition than

soil loss however with no differences between the two streams. Nevertheless along

Mwachakula there is more soil deposition occurring upstream than downstream.

However in terms of gulley occurrence there are no differences along the two streams.

4. Whereas there is a significant (α = 0.05) positive relationship between number of

gardens and soil deposition occurring along the two streams there is no relationship

between number of gardens and gulley volumes. The positive relationship shows that

soil deposition is occurring where there is more cultivation which happens to be within

the distance of 18 metres from the stream. Noteworthy this is where the gardens are

under irrigation and with no form of soil conservation measures.

6.2 Recommendations

1. Further studies could be done to establish the origin of the deposited soils to ensure that

appropriate mitigation measures are applied.

2. Considering the fact that 2007/08 had the highest average rainfall since the previous 10

years and that the streams were within one ecological zone with similar soil

characteristics there may be need to carry out similar studies over a number of years,

under different ecological zones and different soil characteristics to test if the same

relationships would emerge.

3. All irrigation planning may have to seriously incorporate appropriate soil conservation

measures.

4. The Malawi Government may also need to come up with practical regulations on stream

bank protection and mechanisms for enforcing them considering the current food

production-population imbalances that exist



54

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62

APPENDIX 1

Table 7.1: Irrigation Technologies Used

Type of

Technology

Total number of gardens Gardens within 18m

Mwachakula Namanolo Mwachakula Namanolo

Watering can 21 24 17 17

Stream

diversion

2 20 1 19

No irrigation 18 5 14 5

Total gardens 41 49 32 41

Table 7.2: Conservation Measures Used

Conservation

Measures Used

Total Number of Gardens Gardens within 18 metres of stream

Mwachakula Namanolo Mwachakula Namanolo

Elephant Grass 6 1 6 1

Bamboo 2 - 2 -

Sugarcane - 5 - 5

None 33 43 26 41

Total Gardens 41 49 34 47



63

Table 7.3: Observed Buffer Widths (m)

Observed buffer (m)

47 20.4 52.2 52.2

7 3.0 7.8 60.0

6 2.6 6.7 66.7

1 .4 1.1 67.8

3 1.3 3.3 71.1

5 2.2 5.6 76.7

3 1.3 3.3 80.0

1 .4 1.1 81.1

2 .9 2.2 83.3

4 1.7 4.4 87.8

2 .9 2.2 90.0

1 .4 1.1 91.1

1 .4 1.1 92.2

1 .4 1.1 93.3

1 .4 1.1 94.4

1 .4 1.1 95.6

3 1.3 3.3 98.9

1 .4 1.1 100.0

90 39.1 100.0

140 60.9

230 100.0

0

1

2

3

4

5

6

8

9

10

11

12

13

14

17

18

20

30

Total

Valid

SystemMissing

Total

Frequency Percent Valid Percent

Cumulat iv e

Percent



64

Figure 7.1: Observed buffer widths along Mwachakula and Namanolo Streams

30 25 20 15 10 5 0

Observed buffer (m)

60

50

40

30

20

10

0

Fre

qu

ency

Mean = 3.66 Std. Dev. = 6.004 N = 90



65

APPENDIX 2

Figure 7.2: Collapsing of banks along Mwachakula leading to loss of garden area

Table 7.4: Area under cultivation from 1980 to 2002

Year

Garden Area (Ha)

Mwachakula Namanolo Total

1980 3.59 2.26 5.85

1982 4.11 9.14 13.25

1995 6.43 6.78 13.21

2002 2.92 4.27 7.19



66

APPENDIX 3

Table 7.5: Soil Texture differences

Texture

20 cm

depth

Texture

40 cm

depth

Texture

60 cm

depth

Texture

80 cm

depth

Texture

100 cm

depth

Mann-Whitney U 25.500 13.500 13.500 13.000 4.000

Wilcoxon W 70.500 49.500 49.500 41.000 25.000

Z -2.032 -2.692 -2.703 -2.461 -3.114

Asymp. Sig. (2-

tailed) .042 .007 .007 .014 .002

Exact Sig. [2*(1-

tailed Sig.)] .067(a) .009(a) .009(a) .020(a) .002(a)

a Not corrected for ties.

b Grouping Variable: Code

Table 7.6: Bulk Density differences

BD 20

cm depth

BD 40

cm depth

BD 60

cm depth

BD 80

cm depth

BD 100

cm depth

Mann-Whitney U 33.000 36.000 29.500 26.500 19.000

Wilcoxon W 78.000 72.000 65.500 54.500 40.000

Z -1.260 -.662 -1.203 -1.093 -1.410

Asymp. Sig. (2-

tailed) .208 .508 .229 .274 .159

Exact Sig. [2*(1-

tailed Sig.)] .230(a) .545(a) .238(a) .285(a) .180(a)



Table 7.7: Organic Matter differences

OM 20

cm depth

OM 40

cm depth

OM 60

cm depth

OM 80

cm depth

OM 100

cm depth

Mann-Whitney U 17.500 17.000 40.000 36.000 23.000

Wilcoxon W 62.500 53.000 76.000 64.000 44.000

Z -2.436 -2.233 -.331 -.227 -1.006

Asymp. Sig. (2-

tailed) .015 .026 .741 .821 .315

Exact Sig. [2*(1-

tailed Sig.)] .012(a) .026(a) .778(a) .860(a) .350(a)





67

Table 7.8: pH differences

pH 20

cm depth

pH 40

cm depth

pH 60

cm depth

pH 80

cm depth

pH 100

cm depth

Mann-Whitney U 38.000 34.000 30.000 24.500 26.000

Wilcoxon W 83.000 70.000 66.000 52.500 47.000

Z -.882 -.835 -1.176 -1.280 -.722

Asymp. Sig. (2-

tailed) .378 .404 .239 .201 .470

Exact Sig. [2*(1-

tailed Sig.)] .412(a) .442(a) .272(a) .211(a) .525(a)



Table 7.9: Cation Exchange Capacity differences

CEC 20

cm depth

CEC 40

cm depth

CEC 60

cm depth

CEC 80

cm depth

CEC 100

cm depth

Mann-Whitney U 47.500 42.000 38.000 35.000 30.000

Wilcoxon W 113.500 108.000 104.000 101.000 51.000

Z -.152 -.165 -.496 -.317 -.302

Asymp. Sig. (2-

tailed) .879 .869 .620 .751 .763

Exact Sig. [2*(1-

tailed Sig.)] .882(a) .904(a) .657(a) .791(a) .808(a)





68

Table 7.10: Soil deposition and soil texture correlation

Correlations

1.000 .133 -.074 -.074 .258* .115

. .273 .545 .545 .031 .343

70 70 70 70 70 70

.133 1.000 .384** .384** .910** -.399**

.273 . .001 .001 .000 .001

70 70 70 70 70 70

-.074 .384** 1.000 1.000** .350** .529**

.545 .001 . . .003 .000

70 70 70 70 70 70

-.074 .384** 1.000** 1.000 .350** .529**

.545 .001 . . .003 .000

70 70 70 70 70 70

.258* .910** .350** .350** 1.000 -.314**

.031 .000 .003 .003 . .008

70 70 70 70 70 70

.115 -.399** .529** .529** -.314** 1.000

.343 .001 .000 .000 .008 .

70 70 70 70 70 70

Correlat ion Coef f icient

Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N

Soil Deposition

Texture 20 cm depth

Texture 40 cm depth

Texture 60 cm depth

Texture 80 cm depth

Texture 100 cm depth

Spearman's rho

Soil

Deposition

Texture 20

cm depth

Texture 40

cm depth

Texture 60

cm depth

Texture 80

cm depth

Texture 100

cm depth

Correlat ion is signif icant at the 0.05 lev el (2-tailed).*.

Correlat ion is signif icant at the 0.01 lev el (2-tailed).**.

Table 7.11: Soil deposition and organic matter correlation

Correlations

1.000 .174 .219 .323** .323** .323**

. .149 .068 .006 .006 .006

70 70 70 70 70 70

.174 1.000 .784** .497** .497** .497**

.149 . .000 .000 .000 .000

70 70 70 70 70 70

.219 .784** 1.000 .369** .369** .369**

.068 .000 . .002 .002 .002

70 70 70 70 70 70

.323** .497** .369** 1.000 1.000** 1.000**

.006 .000 .002 . . .

70 70 70 70 70 70

.323** .497** .369** 1.000** 1.000 1.000**

.006 .000 .002 . . .

70 70 70 70 70 70

.323** .497** .369** 1.000** 1.000** 1.000

.006 .000 .002 . . .

70 70 70 70 70 70


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N

Soil Deposition

OM 20 cm depth

OM 40 cm depth

OM 60 cm depth

OM 80 cm depth

OM 100 cm depth

Spearman's rho

Soil

Deposition

OM 20 cm

depth

OM 40 cm

depth

OM 60 cm

depth

OM 80 cm

depth

OM 100

cm depth




69

Table 7.12: Soil loss and soil texture correlation

Correlations

1.000 .511** .174 .174 .331 -.268

. .008 .394 .394 .099 .186

26 26 26 26 26 26

.511** 1.000 .399* .399* .527** -.469*

.008 . .044 .044 .006 .016

26 26 26 26 26 26

.174 .399* 1.000 1.000** .210 .623**

.394 .044 . . .303 .001

26 26 26 26 26 26

.174 .399* 1.000** 1.000 .210 .623**

.394 .044 . . .303 .001

26 26 26 26 26 26

.331 .527** .210 .210 1.000 -.247

.099 .006 .303 .303 . .223

26 26 26 26 26 26

-.268 -.469* .623** .623** -.247 1.000

.186 .016 .001 .001 .223 .

26 26 26 26 26 26


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N

Amount of Soil

Deposited or Eroded

Texture 20 cm depth

Texture 40 cm depth

Texture 60 cm depth

Texture 80 cm depth


Spearman's rho

Amount of

Soil

Deposited

or Eroded

Texture 20

cm depth

Texture 40

cm depth

Texture 60

cm depth

Texture 80

cm depth

Texture 100

cm depth



Table 7.13: Soil loss and organic matter correlation

Correlations

1.000 -.352 .149 .130 .130 .130

. .078 .466 .527 .527 .527

26 26 26 26 26 26

-.352 1.000 .000 -.680** -.680** -.680**

.078 . 1.000 .000 .000 .000

26 26 26 26 26 26

.149 .000 1.000 -.733** -.733** -.733**

.466 1.000 . .000 .000 .000

26 26 26 26 26 26

.130 -.680** -.733** 1.000 1.000** 1.000**

.527 .000 .000 . . .

26 26 26 26 26 26

.130 -.680** -.733** 1.000** 1.000 1.000**

.527 .000 .000 . . .

26 26 26 26 26 26

.130 -.680** -.733** 1.000** 1.000** 1.000

.527 .000 .000 . . .

26 26 26 26 26 26

Correlation Coefficient

Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N

Soil Loss

OM 20 cm depth

OM 40 cm depth

OM 60 cm depth

OM 80 cm depth

OM 100 cm depth

Spearman's rho

Soil Loss

OM 20 cm

depth

OM 40 cm

depth

OM 60 cm

depth

OM 80 cm

depth

OM 100

cm depth

Correlation is significant at the 0.01 level (2-tailed).**.



70

Table 7.14: Correlation between 10m3 gullies, number of gardens and soil properties at 20cm depth

1.000 .111 .514* .490 .359 -.092 .068

. .682 .042 .054 .172 .735 .802

16 16 16 16 16 16 16

.111 1.000 .519* .397 .607* .604* -.055

.682 . .039 .127 .013 .013 .841

16 16 16 16 16 16 16

.514* .519* 1.000 .529* .519* .294 -.011

.042 .039 . .035 .039 .269 .966

16 16 16 16 16 16 16

.490 .397 .529* 1.000 .297 .307 -.006

.054 .127 .035 . .264 .247 .981

16 16 16 16 16 16 16

.359 .607* .519* .297 1.000 .292 .255

.172 .013 .039 .264 . .272 .340

16 16 16 16 16 16 16

-.092 .604* .294 .307 .292 1.000 .359

.735 .013 .269 .247 .272 . .172

16 16 16 16 16 16 16

.068 -.055 -.011 -.006 .255 .359 1.000

.802 .841 .966 .981 .340 .172 .

16 16 16 16 16 16 16

Correlat ion Coef f ic ient

Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N

Gulley Volume (m3)

Number of gardens

BD 20 cm depth

CEC 20 cm depth

OM 20 cm depth

pH 20 cm depth

Texture 20 cm depth

Spearman's rho

Gulley Volume

(m3)

Number of

gardens

BD 20 cm

depth

CEC 20

cm depth

OM 20 cm

depth

pH 20 cm

depth

Texture 20

cm depth

Correlat ion is signif icant at the 0.05 level (2-tailed).*.

Table 1 shows the correlation between 10m

3 gullies, number of gardens and soil properties at 20cm depth

Results show that there is no significant (α=0.05) relationship between number of gardens and gullies with volumes less than

10 m3

There is a significant (α=0.05) positive linear relationship between bulk density and both number of gardens and gulley

volumes

There is a significant (α=0.05) positive linear relationship between number of gardens and both organic matter and pH



71


1.000 .111 .487 -.145 .244 .429 .244

. .682 .065 .606 .380 .111 .382

16 16 15 15 15 15 15

.111 1.000 .325 .567* .495 .409 .611*

.682 . .237 .027 .061 .131 .015

16 16 15 15 15 15 15

.487 .325 1.000 -.027 .585* .405 .381

.065 .237 . .923 .022 .134 .161

15 15 15 15 15 15 15

-.145 .567* -.027 1.000 .469 .013 .070

.606 .027 .923 . .078 .964 .804

15 15 15 15 15 15 15

.244 .495 .585* .469 1.000 .108 .121

.380 .061 .022 .078 . .702 .666

15 15 15 15 15 15 15

.429 .409 .405 .013 .108 1.000 .333

.111 .131 .134 .964 .702 . .225

15 15 15 15 15 15 15

.244 .611* .381 .070 .121 .333 1.000

.382 .015 .161 .804 .666 .225 .

15 15 15 15 15 15 15


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N

Gulley Volume (m3)

Number of gardens

OM 40 cm depth

pH 40 cm depth

Texture 40 cm depth

CEC 40 cm depth

BD 40 cm depth

Spearman's rho

Gulley Volume

(m3)

Number of

gardens

OM 40 cm

depth

pH 40 cm

depth

Texture 40

cm depth

CEC 40

cm depth

BD 40 cm

depth





10 m3

There is a significant (α=0.05) positive linear relationship between number of gardens and both bulk density and pH



72


1.000 .111 -.179 .259 .567* .590* .204

. .682 .522 .352 .027 .021 .465

16 16 15 15 15 15 15

.111 1.000 .553* .342 .479 .236 .605*

.682 . .033 .212 .071 .396 .017

16 16 15 15 15 15 15

-.179 .553* 1.000 .483 -.028 -.081 .173

.522 .033 . .068 .920 .775 .538

15 15 15 15 15 15 15

.259 .342 .483 1.000 .104 .046 .104

.352 .212 .068 . .713 .871 .712

15 15 15 15 15 15 15

.567* .479 -.028 .104 1.000 .378 .640*

.027 .071 .920 .713 . .165 .010

15 15 15 15 15 15 15

.590* .236 -.081 .046 .378 1.000 -.013

.021 .396 .775 .871 .165 . .965

15 15 15 15 15 15 15

.204 .605* .173 .104 .640* -.013 1.000

.465 .017 .538 .712 .010 .965 .

15 15 15 15 15 15 15


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N

Gulley Volume (m3)

Number of gardens

pH 60 cm depth

Texture 60 cm depth

OM 60 cm depth

CEC 60 cm depth

BD 60 cm depth

Spearman's rho

Gulley Volume

(m3)

Number of

gardens

pH 60 cm

depth

Texture 60

cm depth

OM 60 cm

depth

CEC 60

cm depth

BD 60 cm

depth





10 m3


There is a significant (α=0.05) positive linear relationship between gulley volume and both organic matter and CEC



73


1.000 .111 .029 .432 .621* -.186 .742**

. .682 .922 .123 .018 .524 .002

16 16 14 14 14 14 14

.111 1.000 .724** .356 .267 .709** .279

.682 . .003 .211 .356 .005 .335

16 16 14 14 14 14 14

.029 .724** 1.000 .239 .372 .619* .292

.922 .003 . .411 .191 .018 .311

14 14 14 14 14 14 14

.432 .356 .239 1.000 .669** .152 .215

.123 .211 .411 . .009 .603 .460

14 14 14 14 14 14 14

.621* .267 .372 .669** 1.000 .009 .553*

.018 .356 .191 .009 . .976 .040

14 14 14 14 14 14 14

-.186 .709** .619* .152 .009 1.000 .252

.524 .005 .018 .603 .976 . .384

14 14 14 14 14 14 14

.742** .279 .292 .215 .553* .252 1.000

.002 .335 .311 .460 .040 .384 .

14 14 14 14 14 14 14


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N

Gulley Volume (m3)

Number of gardens

BD 80 cm depth

CEC 80 cm depth

OM 80 cm depth

pH 80 cm depth

Texture 80 cm depth

Spearman's rho

Gulley Volume

(m3)

Number of

gardens

BD 80 cm

depth

CEC 80

cm depth

OM 80 cm

depth

pH 80 cm

depth

Texture 80

cm depth


Correlat ion is signif icant at the 0.01 level (2-tailed).**.




10 m3


There is a significant (α=0.05) positive linear relationship between gulley volume and both organic matter and texture



74


1.000 .111 -.091 .457 .589* -.194 .744**

. .682 .768 .117 .034 .526 .004

16 16 13 13 13 13 13

.111 1.000 .710** .301 .333 .607* .330

.682 . .007 .317 .267 .028 .271

16 16 13 13 13 13 13

-.091 .710** 1.000 .069 .301 .317 .353

.768 .007 . .823 .318 .292 .237

13 13 13 13 13 13 13

.457 .301 .069 1.000 .576* .273 .352

.117 .317 .823 . .039 .368 .238

13 13 13 13 13 13 13

.589* .333 .301 .576* 1.000 -.163 .669*

.034 .267 .318 .039 . .595 .012

13 13 13 13 13 13 13

-.194 .607* .317 .273 -.163 1.000 .197

.526 .028 .292 .368 .595 . .518

13 13 13 13 13 13 13

.744** .330 .353 .352 .669* .197 1.000

.004 .271 .237 .238 .012 .518 .

13 13 13 13 13 13 13


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N

Gulley Volume (m3)

Number of gardens

BD 100 cm depth

CEC 100 cm depth

OM 100 cm depth

pH 100 cm depth


Spearman's rho

Gulley Volume

(m3)

Number of

gardens

BD 100

cm depth

CEC 100

cm depth

OM 100

cm depth

pH 100

cm depth

Texture 100

cm depth






10 m3


There is a significant (α=0.05) positive linear relationship between gulley volume and both organic matter and texture



75

Table 7.19: Correlation between above 10m3 gullies and soil properties at 20cm depth

Correlations

1.000 .200 -.400 .400 .316 -.258

. .800 .600 .600 .684 .742

4 4 4 4 4 4

.200 1.000 .800 .800 .949 .775

.800 . .200 .200 .051 .225

4 4 4 4 4 4

-.400 .800 1.000 .400 .632 .775

.600 .200 . .600 .368 .225

4 4 4 4 4 4

.400 .800 .400 1.000 .949 .775

.600 .200 .600 . .051 .225

4 4 4 4 4 4

.316 .949 .632 .949 1.000 .816

.684 .051 .368 .051 . .184

4 4 4 4 4 4

-.258 .775 .775 .775 .816 1.000

.742 .225 .225 .225 .184 .

4 4 4 4 4 4


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N

Gulley Volume (m3)

BD 20 cm depth

CEC 20 cm depth

OM 20 cm depth

pH 20 cm depth

Texture 20 cm depth

Spearman's rho

Gulley Volume

(m3)

BD 20 cm

depth

CEC 20

cm depth

OM 20 cm

depth

pH 20 cm

depth

Texture 20

cm depth



76


Correlations

1.000 .000 -.400 -.600 -.105 -.258

. 1.000 .600 .400 .895 .742

4 4 4 4 4 4

.000 1.000 .200 .800 .316 .775

1.000 . .800 .200 .684 .225

4 4 4 4 4 4

-.400 .200 1.000 .400 .949 .775

.600 .800 . .600 .051 .225

4 4 4 4 4 4

-.600 .800 .400 1.000 .316 .775

.400 .200 .600 . .684 .225

4 4 4 4 4 4

-.105 .316 .949 .316 1.000 .816

.895 .684 .051 .684 . .184

4 4 4 4 4 4

-.258 .775 .775 .775 .816 1.000

.742 .225 .225 .225 .184 .

4 4 4 4 4 4


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N

Gulley Volume (m3)

BD 40 cm depth

CEC 40 cm depth

OM 40 cm depth

pH 40 cm depth

Texture 40 cm depth

Spearman's rho

Gulley Volume

(m3)

BD 40 cm

depth

CEC 40

cm depth

OM 40 cm

depth

pH 40 cm

depth

Texture 40

cm depth



77


Correlations

1.000 -.400 .400 -.600 -.316 .211

. .600 .600 .400 .684 .789

4 4 4 4 4 4

-.400 1.000 .400 .400 .949 .316

.600 . .600 .600 .051 .684

4 4 4 4 4 4

.400 .400 1.000 .400 .211 .949

.600 .600 . .600 .789 .051

4 4 4 4 4 4

-.600 .400 .400 1.000 .105 .632

.400 .600 .600 . .895 .368

4 4 4 4 4 4

-.316 .949 .211 .105 1.000 .056

.684 .051 .789 .895 . .944

4 4 4 4 4 4

.211 .316 .949 .632 .056 1.000

.789 .684 .051 .368 .944 .

4 4 4 4 4 4


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N

Gulley Volume (m3)

BD 60 cm depth

CEC 60 cm depth

OM 60 cm depth

pH 60 cm depth

Texture 80 cm depth

Spearman's rho

Gulley Volume

(m3)

BD 60 cm

depth

CEC 60

cm depth

OM 60 cm

depth

pH 60 cm

depth

Texture 80

cm depth



78


Correlations

1.000 -.632 .400 -.800 -.200 .211

. .368 .600 .200 .800 .789

4 4 4 4 4 4

-.632 1.000 .316 .949 .632 .333

.368 . .684 .051 .368 .667

4 4 4 4 4 4

.400 .316 1.000 .200 .000 .949

.600 .684 . .800 1.000 .051

4 4 4 4 4 4

-.800 .949 .200 1.000 .400 .316

.200 .051 .800 . .600 .684

4 4 4 4 4 4

-.200 .632 .000 .400 1.000 -.211

.800 .368 1.000 .600 . .789

4 4 4 4 4 4

.211 .333 .949 .316 -.211 1.000

.789 .667 .051 .684 .789 .

4 4 4 4 4 4


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N

Gulley Volume (m3)

BD 80 cm depth

CEC 80 cm depth

OM 80 cm depth

pH 80 cm depth

Texture 80 cm depth

Spearman's rho

Gulley Volume

(m3)

BD 80 cm

depth

CEC 80

cm depth

OM 80 cm

depth

pH 80 cm

depth

Texture 80

cm depth



79


Correlations

1.000 -.600 .200 -.800 .738 -.105

. .400 .800 .200 .262 .895

4 4 4 4 4 4

-.600 1.000 .200 .800 -.949 .316

.400 . .800 .200 .051 .684

4 4 4 4 4 4

.200 .200 1.000 .400 .105 .949

.800 .800 . .600 .895 .051

4 4 4 4 4 4

-.800 .800 .400 1.000 -.738 .632

.200 .200 .600 . .262 .368

4 4 4 4 4 4

.738 -.949 .105 -.738 1.000 -.056

.262 .051 .895 .262 . .944

4 4 4 4 4 4

-.105 .316 .949 .632 -.056 1.000

.895 .684 .051 .368 .944 .

4 4 4 4 4 4


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N


Sig. (2-tailed)

N

Gulley Volume (m3)

BD 100 cm depth

CEC 100 cm depth

OM 100 cm depth

pH 100 cm depth


Spearman's rho

Gulley Volume

(m3)

BD 100

cm depth

CEC 100

cm depth

OM 100

cm depth

pH 100

cm depth

Texture 100

cm depth



80

APPENDIX 4

Figure 7.3: Collapsing of banks planted to elephant grass



81

UNIVERSITY OF ZIMBABWE · Relationship between stream bank cultivation and soil erosion in Dedza,...

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