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Water harvesting in Kenya

KARI Technical Note No. 16, June 2003

Water Harvesting Technologies in Kenya

Technical Note Series

Itabari, J.K. and Wamuongo, J.W.

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compiled by J Itabari and J Wamuongo

KARI-Katumani, P.O. Box 340 Machakos

KARI HQ, P.O. Box 57811-00200 Nairobi

published 2003

science editing by Rachel Rege

copyediting by John Ayemba

layout design by Irene Kimani

Publications Unit

KARI Headquarters

P.O. Box 57811-00200 City Square Nairobi, Kenya

tel 254 02 4183301-20

fax 254 02 4183344

e-mail [email protected]

publication sponsored by EU/KARI ARSP II

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Contents

1 Introduction .. .. .. .. .. .. 1

2 Water harvesting technologies for crop production .. 1

Modified (enlarged) Fanya juu terraces .. .. 1

Road runoff with canals .. .. .. .. 1

Basins .. .. .. .. .. .. 3

Inundation .. .. .. .. .. 3

Flood diversion .. .. .. .. .. 4

Water spreading .. .. .. .. 4

Contour bunds .. .. .. .. .. 4

Semi-circular bunds (hoops) .. .. .. 6

Negarims .. .. .. .. .. 6

Tied ridges .. .. .. .. .. 8

Trapezoidal bunds .. .. .. .. 8

Microcatchments .. .. .. .. 8

Zai pits .. .. .. .. .. .. 8

3 References .. .. .. .. .. .. 9

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Introduction

Water harvesting is the collection and concentration of runoff water for the production of food crops, pasture and trees, for livestock or domestic purposes. All water-harvesting systems comprise catchment (sources of water) areas and storage components. Catchments include natural slopes or sealed catchments, rocks, roofs, roads and flood water from seasonal rivers. Storage can be either short-term or long-term. Short-term storage is storage in or just above the soil profile whereas long-term storage is deep ponding of water. Short-term storage techniques are usually for crop, fodder, pasture and tree production whereas long-term storage techniques are for domestic and livestock water supplies.

Water harvesting technologies for crop production

Modified (enlarged) Fanya juu terraces

The structure is called Fanya juu (juu is Swahili word for 'up') because during construction, the soil is thrown up-slope to make an embankment which forms a runoff barrier leaving a trench (canal) which is used for retaining or collecting runoff. Conventional fanya juu canals are usually 0.6 m deep and 0.6 m wide. Enlarged fanya juus are about 1.5 m deep and one metre wide. Often, runoff from external catchments (roads, homestead compounds or grazing land) is led into the canals which act as retention ditches allowing water more time to infiltrate the soil. Crops such as bananas, pawpaws, citrus and guava are grown in the ditches. This technique is widely practised in Machakos and Kitui Districts, and has proven effective in water harvesting on slopes greater than 5% where other water harvesting techniques are not recommended.

Road runoff with canals

This technique involves diversion of road runoff into a canal network in the farm. The canal should be about 1.5 m deep and one metre wide, and the distance between adjacent canals about 2 m. It is being practised in areas with ground slopes of more than 5%, mainly in Kitui, Machakos and Mwingi Districts. Bananas are planted in the canal, while fruit trees including pawpaw are planted between the canals together with food crops like beans during the rainy season. The technique is also called banana canal because bananas are invariably planted in the canal.

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Road runoff with canals

Canal Channel about 1.5 m deep and 1 m wide

Banana plants in the channel

About 2 m planted with pawpaw or drought

Discharge point/spillway (vegetated)

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Basins

These are well-levelled rectangular or square structures with runoff from roads diverted into them. The principle is similar to surface irrigation with basins. Their sizes range from 5 x 5 m to 5 x 12 m. The embankments are about 20-30 cm high and 30-45 cm wide. The technique is widely practised in Taveta Division of Taita-Taveta District. The main crops grown using this technique include maize, beans and pigeonpeas. The technique is also practised in Baringo District.

Inundation

The technique involves runoff collection behind a bund and leaving the water standing until the planting date for the crop approaches. The land is then drained and the crop is sown and grows to maturity using the water stored in the soil. This technique also includes naturally occurring short-term flooding in plains and valleys. Sophisticated systems may include a series of bunds with sluice gates and spillways to create several flood areas. This technique requires deep soils with a high water holding capacity to retain adequate water after flooding. The selection of suitable cultivars is important as the soils may be poorly aerated early in the growing period. The technique was introduced in Turkana District in 1951.

Basins with road runoff harvesting

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Flood diversion

This technique is similar to inundation because it involves construction of structures to retain floodwater. However, it differs from inundation in that, in addition to the barrage or weir to divert the floodwater, it also includes diversion of the water to appropriate areas with appropriate conveyance systems. The conveyance systems may be simple, open furrows or lined canals.

Thus, flood diversion is a system of irrigation, but on a seasonal basis. The technology is in Baringo and Turkana Districts for the production of grain crops including sorghum.

Water spreading

This technique entails constructing a small diversion structure across a seasonal watercourse and the use of short bunds to spread the flow without causing erosion. The technique is practised in Turkana District where alluvial and colluvial soil fans at the base of ridges, escarpments or piedmont plains, seasonal stream banks and natural depressions have been used to grow sorghum and millet.

Contour bunds

These are small earth or stone embankments constructed along a contour line. The embankments trap the water flowing down the slope and retain it behind the bunds. The area behind the bunds can be levelled to ensure homogeneous infiltration. The interval between the contours is variable depending on slope

Flood diversion

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and soil type. They can be constructed manually or mechanically. The embankment traps the water flowing down the slope. Attempts to promote the technique have been undertaken in Isiolo and Laikipia Districts, mainly by NGOs.

Catchment area

Spillways Cropped area

Runoff

Contour bund

Collection arm

Contour bunds

Stream

Weir

Bund

Water spreading

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Semi-circular bunds (hoops)

These are semi-circular earth embankments with tips of the bunds on the contour. Water is collected within the hoop from the area above it and confined to the depth defined by the height of the bund and the position of the tips. Excess water is discharged around the tips. The field layout provides for staggered hoops so that runoff from one row is intercepted by the row below it. The size of the cultivated area enclosed by the structure depends on the amount of rainfall. These structures are common in Turkana District and have been tried in Baringo District. They are used for reseeding of grass, fodder shrubs and trees.

Negarims

These are small V-shaped embankments with the apex at the lowest point. Water is collected from the V-shaped basin and stored in the soil profile at the apex. This technique is best for the establishment of trees and shrubs. The catchment area ranges from 16 m2 in agroecological zone (AEZ) V to 1000 m2 in AEZ VII. The embankments are 15-20 cm high. The basin at the apex is 40 cm deep. The technique has very little conveyance losses as water is used close to the source. The structures are also cheap to construct. The technique has been used for establishing trees and for sorghum production in Turkana District. Some farmers also use the technique to grow fruit trees, e.g. mangoes and pawpaws in Kitui and Mwingi Districts.

Semi-circular bunds (hoops)

Embankment area

Catchment area

Earth embankment

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Negarims (above) and Trapezoidal bund (below)

Approximate contour

Crop

Catchment area

Runoff

Earth embankment

Catchment

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Tied ridges

Tied ridges are made mainly to increase surface storage and to allow more time for rainfall to infiltrate the soil. The technique consists of covering the whole soil surface with closely spaced ridges in 2 directions at right angles so the ground is formed into a series of rectangular depressions. The cross ties are usually lower than the ridges so that if the depressions fill and overflow, runoff will be along each ridge and not down the slope.

Trapezoidal bunds

These are trapezoidal shaped earth embankments. The tips of the embankments are placed on the contour line and the base along the lowest contour. The embankment top is level and higher than the ground level at the tips. Water flowing down-slope is trapped and retained behind the bund up to the level of the tips, and any excess overflows around the tips into other bunds in the system or natural drainage course. The size of the enclosure depends on slope and may vary from 0.1 to 1 ha. The embankment base width varies from 2.6 to 5.8 m.

Microcatchments

The microcatchment technique involves spreading runoff from part of land on to adjacent cultivated land without using any structures. The part from which runoff is obtained is weeded to reduce surface evaporation and can be compacted to reduce infiltration, thereby increasing runoff. The soil in the cultivated area is loosened to increase infiltration. The ratio of the catchment to cultivated area usually varies from 1:1 to 5:1 depending on the rainfall regime, soil properties and crop water requirement. There have been attempts to promote this technique in Baringo and Turkana Districts. Research work in semi-arid areas of eastern Kenya has shown that it is possible to increase the yields of most crops by 30-90% using this technique (Gibberd, 1993; Itabari et al., 2000).

Zai pits

This technique is an indigenous method of water harvesting in Burkina Faso, and was recently introduced in Kenya. It involves digging small pits, about 30 cm in diameter and 15-20 cm deep and placing manure or compost at the bottom of the pit prior to planting. During digging, the soil is thrown down-slope to form a small embankment. The pits are also simply referred to as planting pits. Seeds are planted around the bottom of the pit.

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References

[1] Gibberd, V. (1993). Final report EMI dryland farming and dryland applied research project, 1998-1993.

[2] Itabari, J.K., Kitheka S.K., Maina J.N. and Wambua J.M. (2000). Influence of runoff harvesting on maize yield in semi-arid Eastern Kenya. KARI-Katumani Annual report 2000.

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The KARI Technical Note Series provides an outlet for technical work generated by KARI that has not been published in any of the Institute's existing publica-tions that include the East African Agricultural and Forestry Journal and the KARI annual report. The articles may be on completed or ongoing work. The Series carries advisory technical information intended to benefit various stake-holders on research findings generated by the Institute. Contribution to the Series is limited to KARI staff and collaborators. Manuscripts should be sub-mitted to the director KARI.

Other Notes in this series

▪ Integrated helminth control (2)

▪ Water hyacinth: distribution, impact and control measures (3)

▪ Development of sustainable seed potato programme in Kenya (7)

▪ Improved management of indigenous chicken (8)

▪ Legume seed production in western Kenya (9)

▪ Biogas production (10)

▪ Acidic soils in Kenya: constraints and remedial options (11)

▪ Legume cover crops research in Kenya (12)

▪ Development of gladioli and lilies for local and export markets (15)

▪ Water harvesting technologies in Kenya (16)

▪ Indigenous chicken production manual (17)

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