Zambia Rpt01

ASSESSMENT OF POLLUTION AND VULNERABILITY

OF WATER SUPPLY AQUIFERS OF AFRICA CITIES

A CASE FOR

JJOOHHNN LLAAIINNGG,, MMAASSSS MMEEDDIIAA AANNDD MMIISSIISSIIAARREEAASS

IN

LLUUSSAAKKAA,, ZZAAMMBBIIAA

GRZ

Woodlands

City Centre

BauleniJohn Laing

Chunga

Mandevu

Show grounds

Kamanga

Chawama

N

Emmasdale

Grea

t Nor

th R

oad

5 km

Great East Road

Mtendere

Built-up area

CITY BOUNDARY

Kanyama

Perspective views of parts of the city of Lusaka

Map of Zambia showing the

location of Lusaka

Map of the City of Lusaka

Interim Report Page i Lusaka Project

ACKNOWLEDGEMENTS

This project was made possible by the generous support of United Nations Educational Scientific and

Cultural Organisation (UNESCO), United Nations Environment Programme (UNEP) and United Nations

Human Settlements Programme (UN-HABITAT) with support of the Government of the Republic of Zambia

(GRZ) through the Ministry of Energy and Water Development (MEWD).

A s s e s s m e n t o f p o l l u t i o n S t a t u s a n d V u l n e r a b i l i t y o f W a t e r S u p p l y A q u i f e r s o f A f r i c a n c i t i e s

Interim Report Page iii Lusaka Project

ABBREVIATIONS AND ACRONYMS

AET Actual Evapotranspiration

CBoH Central Board of Health

ECZ Environmental Council of Zambia

ETpot Potential Evapotranspiration

GRZ Government of the Republic of Zambia

GWR Groundwater Recharge

ITCZ Inter-Tropical Convergence Zone

LCC Lusaka City Council

LWSC Lusaka Water and Sewerage Company

SRO Surface Runoff

UN-HABITAT United Nations Human Settlement Programme (formerly UNCHS (Habitat))

UNEP United Nations Environment Programme

UNESCO United Nations Educational, Scientific and Cultural Organisation

UNZA University of Zambia

WHO World Health Organisation

ZAB Zaire Air Boundary

At a water point in Misisi Compound


Interim Report Page 1 Lusaka Project

1 INTRODUCTION

From its earliest days of settlement in the early 1900s, the suitability of Lusaka’s location has been a

source of great controversy, the major one having been hitherto the nature of the bedrock and the

hydrogeologic regime underlying the city. Even during the city’s founding, it usually experienced periodic

rises of the water table close to the ground surface, causing occasional flooding.

Consequently, the city has experienced rapid population growth resulting in unplanned settlement

patterns. This population has grown from only about 195,700 at independence in 1964, rising to about

536,000 in 1980, and about 769,000 in 1990. In the year 2000, the city population was estimated at two

million (Fig. 1).

1.1 LOCATION AND GEOMORPHOLOGY

The city of Lusaka (Fig. 2) was established as a rail siding in 1905 and because if its central location, it

was inaugurated the new capital city of Zambia (then Northern Rhodesia) on 31 May 1935. The topography

of Lusaka is characterised by a plateau to the south and west standing at an elevation of 1,200 metres,

while flat-topped hills to the north and east of the city stand at an elevation of about 1,300 metres above

sea level. The city’s topography and morphology have been greatly influenced by the underlying geology.

Fig. 1: Population figures for the city of Lusaka (1964 – 2000)

196000

536000

769000

2000000

0

400000

800000

1200000

1600000

2000000

1964 1980 1990 2000



Fig. 2: Location of the city of Lusaka

1.2 CLIMATE

The city experiences a sub-tropical climate that is strongly seasonal. It has three distinct seasons, namely:

a) A cool dry season from mid-April to mid-August with mean day temperatures varying between 15oC

and 23oC. Minimum temperatures may sometimes fall below 10oC in June and July.

b) A hot dry season lasting from mid-August to mid-November. During this period, day temperatures may

vary between 27oC and 38oC.

c) A warm wet season from mid-November to mid-April during which time 95% of the annual rainfall

takes place. The annual rainfall averages about 800 mm/a.



2 GEOLOGY

Rocks underlying the city of Lusaka consist of schists interbedded with quartzites and dominated by thick

and extensive sequences of marbles (Fig. 3), with the latter being generally referred to as the Lusaka

Dolomites or Lusaka Limestones.

Fig. 3: Geologic map of the city of Lusaka

2.1 IMPORTANT GEOLOGICAL STRUCTURES

The main structures in the area trend SE – NW and they appear to have developed as a result of repeated

overthrusting (Fig. 4), which coincides with the main SE –NW trend. Associated with these tectonic

activities are three sets of joints, whose presence and those of other discontinuities, has enabled water to

be transmitted through the rock mass, causing differential and preferential dissolution of the marbles and

the subsequent development of an integrated and well-developed system of conduits and solution

channels. Development of cavities in these rocks appears to follow the main fracture-direction from south-

east to north-west as depicted in Figure 5.



2.2 EVIDENCE FOR MAJOR GEOLOGIC STRUCTURES

Generally, evidence for the presence of major geologic structures, particularly discontinuities in these

rocks, is exhibited by some recognisable surficial features, such as lineaments and the association of

sinkhole-distribution with zones of high lineament density.

The regional scale relationship of karst features to lineaments is further evidence of the important role

fracture zones have assumed in the process of solution weathering. Fig. 6 shows the distribution of

sinkholes and the dispersion of their orientation demonstrates the effect of complex folding in the Lusaka

area, while the apparent correlation of sinkhole distribution with zones of high lineament density is

depicted in Fig. 7.

Fig. 6: Karst geomorphology of the Lusaka marble plateau

SE

Fig. 4: Schematic model showing repeated thrustingin the Lusaka area (Modified after Nkhuwa, 1996).

Fig. 5: A display of well-developed system ofconduits and solution channels in the Lusakamarbles

Projectareas



Fig. 7: The relationship between lineaments and sinkhole manifestations. After Nkhuwa, 1996

The presence of these discontinuities has enabled water to be transmitted through the rock masses,

causing differential dissolution in the meta-carbonates and the subsequent development of an integrated

system of conduits and solution features. This has riddled the terrain with collapse and subsidence

sinkholes.

Other than converting the meta-carbonate rocks into an important and comparatively cheap source of

water supply, such characteristics have also transformed this terrain into one with specific and highly

complex hydrogeologic and environmental conditions that now pose several potential hazards to the city

aquifers. In turn, these conditions impose enormous restrictions on land use practices of this city terrain.

Project areas



3 RAINFALL

The arrival of the rainy season from about late September lasting through to May is generally coincident

with a number of air-circulation patterns that influence the Lusaka region. The advent of these patterns,

consisting of the Angolan Low, the Zaire Air Boundary (ZAB) and the Intertropical Convergence Zone (ITCZ),

introduces air that is moist, unstable and confluent or convergent. Although these patterns generally

arrive at different times, they usually overlap with and influence each other.

The Lusaka plateau receives an annual average of 800 mm of rainfall. Fig. 8 shows the annual rainfall for

the period 1971/72 to 2000/2001, with 819.7 mm/a representing the average rainfall. Table 1 depicts

the monthly rainfall distribution during the same period.

0

200

400

600

800

1000

1200

1400

1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001

Annual Rainfall (mm)

Mean Annual rainfall = 819.7 mm

Fig. 8: Distribution of the average annual rainfall over the Lusaka plateau (1991/92 – 2000/01)

Table 1: Average monthly precipitation (in mm) for the Lusaka area [1971/72 - 2001/02]

Month Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total

Rainfall (mm) 0.0 0.0 2.9 15.6 76.8 181.9 222.9 183.5 102.1 30.8 2.8 0.2 819.7

From Figure 6, one important aspect of the annual rainfall variability relative to the average annual

rainfall on the Lusaka plateau is the tendency for sequences of relatively wet and dry years to occur. It is

apparent from this diagram that 1971, 1973, 1974, 1975, 1977, 1979, 1980, 1988, 1989, 1990, 1996, 1998,



1999 and 2000 represent wet years.

The years 1972, 1976, 1978, 1981, 1982, 1983, 1984, 1986, 1987, 1991, 1992, 1993, 1994, 1995, 1997 and

2001 are dry, with all but four occurring in the 1980s and 1990s. Their dryness, particularly in the 1990s,

appears severe both in terms of amount and duration.

3.1 DRAINAGE

The Lusaka plateau forms part of the mid-Tertiary (Miocene) peneplain of central Africa (Dixey In:

Drysdall, 1960), which here stands at about 1,200 metres. The flat-topped hills to the north and east of

the city standing at about 1,300 metres are postulated to be remnants of an earlier peneplain of

Cretaceous age.

Drainage of the area reveals an essentially radial pattern (Fig. 9). This pattern appears consistent with the

domical-type relief, which conforms to the basin and swell structural concept applied by HOLMES (1965)

to explain the relief of Africa, with the Lusaka plateau forming a minor swell.

One of the most conspicuous features of this plateau is the scarcity and/or complete lack of surface

drainage particularly in its central part. Thus, rainwater drains into fissures and/or infiltrates through the

overburden to join the underground water. Only surface water in excess of the infiltration capacity is

drained into minor seasonal streams.

Fig. 9: Map showing the city boundary, topography and drainage of the Lusaka plateau.



3.2 POTENTIAL EVAPOTRANSPIRATION, ETPOT

According to Veihmeyer (1964), if water were available in unlimited supply, the amount that would

evaporate and/or transpire would express the potential evapotranspiration (ETpot). This value expresses a

maximum water loss, a temperature dependent quantity and a measure of the moisture demand for a

region. Potential evapotranspiration values for the Lusaka plateau, determined by the Thornthwaite

Formula, are presented in Table 2. The Thornthwaite Formula is based on an exponential relationship

between mean monthly temperature and mean monthly consumptive use as follows:

ETpot = 16 ∗ a

Jt

∗10 (mm d-1)

Where: t � average monthly temperature (oC); J � Heat index, the sum of 12 months’ values of ( ) 514.15

t thus, J � [ ]∑12

1

514.1

5t ;

a =

Jlog4232459.29262188.0

− or a = 6.75 ∗ 10-7 ∗ J3 – 7.71 ∗ 10-5 ∗ J2 + 1.792 ∗ 10-2 ∗ J + 0.49239

For the period under review, values obtained from the Thorntwaite Formula and corrected by a factor that

varies with the number of days in a month and geographic location, are given in Table 2.

Table 2: Potential evapotranspiration values calculated by the Thorntwaite Formula.

Month Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total

Rainfall (mm) 0 0 2.9 15.6 76.8 181.9 222.9 183.5 102.1 30.8 2.8 0.2 819.7

Temp (oC) 16 18 22 24 23 22 21 21 21 20 18 16 Average20

ETPot (mm) 43 60 88 114 107 99 95 81 84 71 56 40 938

A comparison of monthly potential evapotranspiration values with rainfall figures (Fig. 10) shows three

important periods in which the rainfall is:

a) Less than potential evapotranspiration, in which case, there is a resultant water deficit. During times

of such water deficiencies, plants on the Lusaka plateau shed off their leaves as a measure to reduce

evapotranspiration.

b) Equal to potential evapotranspiration, giving no resultant change in the soil moisture content, and

cc)) Greater than potential evapotranspiration, resulting in a net excess in the soil water content, in

which case, that part of the rainfall, which is not evaporated, enriches the moisture content of the

soil until the field capacity is attained. Excess water, after fulfilment of the field capacity, trickles

down to the groundwater store.



0

50

100

150

200

250

Jul Aug Sep Oc t Nov Dec Ja n Feb M a r Ap r M a y Jun

0

5

10

15

20

25

30

Ra infa ll (mm)

PET* (mm)

Temp (oC)

Rain

fall a

nd E

T po

t (m

m) Tem

pera

ture ( 0C)

M o nths o f resultant water def ic it and so il

mo isture depletion

M o nths o f net excess in so il water

co ntent and so il mo isture recharge

3.3 Actual evapotranspiration, AET

Actual evapotranspiration (AET) constitutes the quantity of water used annually by either cropped or

natural vegetation in transpiration or in the building of plant tissue. Another component of AET is drawn

directly from the soil and from rainfall intercepted by plant foliage (Veihmeyer, 1964).

One of the methods used to determine AET is that of TURC (In: MATTHESS & UBELL, 1983). It takes into

account annual precipitation and the average annual temperature, as follows:

AET =

+

R

RJ

0 92

.

[mm a-1]

Wherein:

R = annual rainfall [mm]; J = 300 + 25 ∗ t + 0.05 ∗ t3 = 820; t = mean annual temperature [0C].

This gives an annual AET-value of 594.8 mm. This may also be regarded as representing the long-term

average for the period of 31 years (1991/92 – 2000/01) under review.

3.4 GROUNDWATER RECHARGE, GWR

Groundwater recharge constitutes a special hydrologic component particularly in the consideration of

groundwater resources in the Lusaka aquifer. Therefore, its quantitative determination becomes critical in

Fig. 10: Relationship among rainfall, potential evapotranspiration and temperature over the Lusaka plateau



the planning, exploitation use and possible threats to quality and quantity of the available water

resources.

In Lusaka, recharge is derived from rainfall, which falls directly on the plateau. When rain falls on the soil

surface, both gravity and capillary potential tend to cause its downward movement by infiltration.

Although earlier studies have indicated the recharge area to lie south-east of the city, the presence of

well-developed karstic features over the entire marble terrain would indicate that recharge occurs over

the whole city area underlain by the marble. The conspicuous lack of permanent surface-drainage over

the Lusaka plateau is evidence that the area imbibes most of the rain water that falls on it, which implies

that the area is mainly drained underground except during periods of excessive rains, when rates of

infiltration may be overwhelmed.

However, very little information is available about groundwater levels in the Lusaka aquifer because there

are piezometers or wells from which these recordings would be obtainable, other that those from which

groundwater is abstracted for supply to the city. In addition, measuring gauges that would allow

determination of groundwater levels as influenced by precipitation are not available. Consequently, the

estimation of groundwater recharge is only based upon general hydrological parameters, mainly

precipitation, potential and actual evapotranspiration.

On the basis of the acquired and calculated hydrologic data, the components of total runoff (STRO), which

is composed of groundwater recharge (GWR) and surface runoff (SRO), can be determined as follows:

GWR + SRO = R – AET (mm/a)

GWR + SRO = 819.7 – 594.8 (mm/a)

GWR + SRO = 224.9 (mm/a)

Because of problems pertaining to the partitioning of GWR and SRO, two optimistic assumptions have been

made as regards the amount of groundwater recharge:

• That the total runoff constitutes groundwater recharge. The ubiquitous lack of surface drainage on the

Lusaka plateau may justify the assumption.

• The calculated total runoff of 224.9 mm/a represents 27% of the annual rainfall. Coincidentally, Von

HOYER at al. (1978) and UBELL (1961) determined for the Lusaka and Hungarian karst areas,

respectively, that groundwater recharge contributes 22% of the total annual rainfall. Implicitly,

although the two areas lie in different geographic and climatic zones, similarities in quantities of

groundwater recharge would probably be compensated by components of runoff and

evapotranspiration. On the basis that 22% of the annual precipitation constitutes recharge, a resultant

annual replenishment to the groundwater store of 180 mm is attainable.

Thus, a conservative arithmetic average of 180 mm per annum constitutes the long-term groundwater

recharge for the Lusaka plateau. For a total surface area of 680 km2 for Lusaka and its environs, an

average of 122 ∗ 106 m3/a recharge may be assumed to have infiltrated to the groundwater store during



the period under review.

The observation of water levels in some of the Lusaka Water and Sewerage Company (LWSC) boreholes for

a period of seven years (1995-2001) indicates a general rise of groundwater levels between December and

January (Figs. 11), which is also indicative of the time the field capacity in the soils is attained. This

implies that rainfall events at the beginning of the rainy season contribute wholly towards

evapotranspiration as well as replenishing soil moisture.

-40

-35

-30

-25

-20

-15

-10

-5

0

Jan'

95

Ap

r'95

Jul'9

5

Oct

'95

Jan'

96

Ap

r'96

Jul'9

6

Oct

'96

Jan'

97

Ap

r'97

Jul'9

7

Oct

'97

Jan'

98

Ap

r'98

Jul'9

8

Oct

'98

Jan'

99

Ap

r'99

Jul'9

9

Oct

'99

Jan'

00

Ap

r'00

Jul'0

0

Oct

'00

Jan'

01

Ap

r'01

Jul'0

1

Oct

'01

0

50

100

150

200

250

300

350

400

Ra infa ll

Level

Rainfall (m

m)

Wat

er le

vel b

elow

gro

und

surfa

ce

(m)

Fig. 11: Response of the groundwater table to rainfall in one of the Lusaka Water and Sewerage Company

boreholes (1995 – 2001)

Thus, if the water table is close to the surface and sufficient water is supplied, the moisture may

reach the water table and add to the groundwater.

Zambia Rpt01

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