Microcatchment Interrow Water Harvesting

Interrowand ContourBench Terraces

Unit 9

Microcatchment Interrow Water Harvesting

INTERROW WATER HARVESTING

= 1 - 3 m²Runoff area :

• smoothing

• compaction

• sealing with

salts or other

• sealants

• weeding > 200 -500 mm/yr = 1 : 1 to

= 0.3 - 1 m²

5 : 1= 0 - 5 %

soil depth > 1 m

Millet, maize, beans, grapes, olive trees


Unit 9

Interrow Water Harvesting

Flat terrain 0 -1 % slope

compacted bunds alternating strips

Slopes 1- 5 % slope


Unit 9


Runoff

Runoff orchard, New Mexico; Photo: Frasier


Unit 9


Cropped and compacted strips, Syria; Photo: Oweis

1.4 m 1.4 m


Unit 9CONSTRUCTION :• (by hand), rollers or tractors


Runoff

Runoff orchard, New Mexico

Cropped and compacted strips, Syria

1.4 m

1.4 m

ADVANTAGES :• can be fully mechanized

LABOUR DEMAND :• high (if manually implemented)

DISADVANTAGES :• high rainfall intensities may cause

erosion on the cropped strips


Unit 9

Forms of interrow water harvesting on flat land; Source: Prinz 1986

On flat land :


croppingarea

Runoff area compacted

incre

asin

g a

rid

ity


Unit 9

Microcatchment : Contour Bench Terraces

CONTOUR BENCH TERRACE

Trees, bushes, annual crops

= 2 - 20 m²

= 200-600 mm /yr= 1 : 1 to

= 2 - 10 m²

10 : 1

= 20 - 50 %

• even cropping area

• drain

• lip

• water retardation

• prevention of

soil erosion

drain

catchment

lip


Unit 9

Microcatchment : Contour Bench Terraces

Different types of contour bench terraces

Level bench

Sloping bench

Drain optional

catchment

lip

drain


Unit 9

DIMENSIONS :

• strip width depends on slope

Contour Bench Terraces

CONSTRUCTION :

• manual

• by animal

• tractors or bulldozers

LABOUR DEMAND / COST :

• high

LIMITATIONS :

• bare surfaces increase runoff but enhance erosion

Contour bench terraces for waterharvesting; Source: Hurni 1986


Unit 9

Construction of Contour Bench Terraces

Construction:

Source: Rocheleau 1988; adapted

Riser

Heel

Fill Toe-drain

Topsoil and original surface

Subsoil

PegsStep OneEstablish pegs on contour

Step TwoRemove topsoiland place up slope

Step ThreeExcavate and re-site fill

Step FourReplace topsoil


Unit 9

Details of bench terraces with 1 m vertical interval; Source: FAO 1976

Slope % 5 10 15 20 25 30 35

Width of bench terrace (m)Width of cropping area (m)No of benches / 100 m of slopeMax. depth of cut (m)Catchm. area of riser /ha (m_)

2018.55

0.47919

108.510

0.451838

6.75.215

0.422758

53.520

0.403667

4.2.525

0.374596

3.31.830

0.355515

2.91.435

0.326434

Contour Bench Terraces

Given different soil depth (a, b) :

gentler slope wider terraces

Determine terrace width by soil depth and slope

Given different

slopes (b, c) : greater soil depth wider terraces


Unit 9

`Linear´ Microcatchments - Comparison

terraces

contour ridges

interrow WH

increasing slope


Unit 9• Interrow WH involves the compaction of the catchment and the

establishment of catchment strips and cropping strips

• Contour bench terraces can be used on steeper slopes than

interrow water harvesting or contour bunds

• Contour bench terraces have a drain and a lip

• Interrow water harvesting and contour bench terraces require

a high labour input

Summary

Microcatchment Interrow Water Harvesting

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