Eng6

Jfuas No.2 December 2013

77

Review of Water Harvesting Techniques for theImprovement of Crop Production in North Darfur StateSalih Ahmedai Abdalla, Faculty of Environmental Sciences and Natural Resources

University of Al-Fashir, Sudan

إنتاجية لزيادة المياه حصاد تقنيات إستخدامدارفورالمحا شمال والية في صيل

א�� WJ

�� א�� א� �� א�� א�� א�� א �� א*()'&�Kא�$#"! א��,+ ,.א- � א�� /�0��!�1�2� �3�45� 6#�� 7 80 א�� א�.�א:��6א�)9" א*()�; � א?��!א��<Kא*=$�> �� א?��! @

�B8A(א- CDE(� �F ��Eא� ��EGא H�'IJ � �KLK(D� �3�: Mא��ND� �O�(א�P�'א� ��N,� �LQא� �)�' H�'�#5K

H�'�#5 -8A(B�L R�:�א�.א -�#�� N,P�'א� �S)@��> T:�א��U'$6א��V)� א�D'IW(-�6א��א��4 X�B� �<�א� "')8J T� +J�(א� YD:�6א�א:�Z �

H�[�8א�K� \�Qא�� א?$�[� T� "�J �8: 8[��L��א� M�^אK� -8A(��"')8Jא�� -�2)�U'$6א��,�� _:�Z `',2000> �:QL ��(W1�G�8�:א�Z a� bDJ

300� ��(W1@��> T: R��א� bDא��D��(6א��I�'L א��8 T� �'�']� �:�5 T�א�� -�2) -8A(�56D'IW(א� א��4�-�� X�B /��c�K� !��Kא*א�_)�J �'[�()

��8'D#(א� א�.�א:'� X�EL �)��#� !"�J� ��4�K!"9 �d)eL H�'�#(א� PK1 fN(5b&?אCg H�'�#(א� PK1 CD[ 8�:� h:�א.ID� i��N(0� �$DW� "j�b�8#5

��א�)�]' ��k��K!א*� �LQD� 6L�>א�� (lא !��Z � � 8:��5 H�'�#(א� PK1�+'�lא ��'(mא n� +'��ID� א*()�]'� !��Z� �' א � P�'א� ��K95� �LQא� �L�Nm

Bא� YD: 8:��5 � Rא�'�D� fD4א� � �5� oUא�� 4��B�'D�א�# H�L��?א p�#א�� )#�א��T� א��'�qא?8 ��185� Kא�$#�

الفارش م2013ديسمرب–الثا*العدد-التطبيقيةالعلوممجلة–جامعة

78

Abstract

The climatic zones of Darfur region are characterized by low

rainfall in the northern parts desert and semi-desert and moderate to

high rainfall in the southern parts. North Darfur State lies in the Sahel

zone. This zone is about 800 km wide and has a dry period of up to 9

months. It is characterized by a recurrent periodic drought, traditional

rain-fed agricultural production and low yield per unit area. Runoff is

the main source of surface and ground water. Water resources

assessment showed that there are vast amounts of ground water with

good to excellent quality which can be used for crop production.

Under erratic rainfall conditions in the semi-arid zone of sub-Sahara

Africa, a major contribution to improve crop production can be

anticipated from improved and up- scale soil water conservation and

rainwater harvesting practices. Rainwater harvesting is essential for

supporting sustainable crop production in sub-Sahara Africa facing

climatic change impacts. Supplementary irrigation is practiced in Sag

El Naam project. Flood diversion is practiced in Kidinir area using a

canal for diverting flows to 8 km and annually 2000 ha were being

irrigated. Spread irrigation systems like hafirs surrounded by

embankment for collection of floodwater, with siphon inlet provided

with sluice gate and off-spreading were practiced along the wadis. In

Malam El Wadayin project the water stored in the dam was diverted

by two canals to irrigate 300 ha. These practices improve

hydrological indicators such as infiltration and groundwater recharge.

Nutrients and biomass increase with subsequent higher yields. Higher


79

biomass supports a higher number of plants and animals, although

native species might be replaced by crops as the landscape might

change as a whole. This might trigger conflicts between nomadic and

sedentary population. Use of micro catchments, water spreading

techniques and introduced new technologies offer opportunities for

runoff farming .Early maturing varieties adapted to the environment

with their higher yields were preferred for providing the farmers with

subsistence food and fodder for their livestock.

1-Introduction

North Darfur State lies between latitudes 12º N and 20º N and

longitudes 21º 52′ E and 27º 54′ E. Its population is 1.3 million

according to 1993 census. The State is located on the southern edge of

the Sahara desert and falls within the arid climatic Sahel zone, which

extends from the Atlantic coast of West Africa to the Sudan. The

boundaries of the Sahel are demarcated by the 100mm and 600mm

isohyets average annual rainfall. In the Sahel zone three precipitation

regimes are recognized, the sub-desert > 200mm, the typical Sahel

200-400mm with a rainy season of 2 to 2.5 months and the Sahel of

Sudanese border (400-600mm). The rainy season extends from May to

October with a peak in August. The rainfall fluctuates in north and

middle parts of the state. There are many Wadis (seasonal stream),

which drain large amounts of surface runoff and its use is very limited

in runoff farming and agricultural production. There are three types of

soils classified as sandy, loam and clay. Sandy soils have a high

infiltration rate, but low retention capacity. It consists of 60% coarse


80

to fine sand and less than 10% clay. Loamy and clay soils cover

limited areas. The most suitable soils for water harvesting are

generally medium- textured, deep loam soils (2m) with the capacity to

store the harvested runoff water. Sodic and saline soil zones which

have excess soluble salts should be avoided. People practice rain-fed

shifting cultivation on sandy and clay soils. They cultivate sorghum,

millet, sesame and groundnuts during the rainy season and they keep

livestock. Traditionally, farmers practice a type of rotating fallow

agriculture, which leaves portion of the land with some form of

ground cover. The term water harvesting is used to describe the

technique of collecting and storing water for later beneficial use from

an area modified to increase precipitation runoff. The collected water

can be used for domestic and animal uses and for crops growing. All

water harvesting systems have a catchment area for collecting and

concentrating the precipitation and storage facility for holding the

collected water. A typical storage technique can be an earth reservoir,

lined pits and various steel, plastic, concrete or wooden tanks.

The first water harvesting technique was nothing more than

depressions in a rock surface that trapped rainwater. These water

depression storage facilities are still found in many parts of the world

and serve as drinking water supplies for many forms of wild life. It is

highly probable that the first constructed facility was simply an

excavated pit or other water storage container at the outfall of rocks.

Water harvesting is defined as: "the complete facility for collecting

and storing the runoff water” (FAO, 1994). UNEP (1983) defined


81

rainwater harvesting as: "the deliberate collection of rainwater from

surface catchments and its storage to provide a supply of water”. A

similar definition was given by International Water and Sanitation

Center (IRC, 1992) in which rainwater harvesting is defined as: "the

collection, concentration and storage of water that runs off a natural or

man-made catchments surface". These are generalized definitions

which depend on generation, collection and utilization of surface

runoff for agriculture or domestic use.

The objectives of the study to assess the relationship between

precipitation and crop production and collecting data and information

about the state. Also includes identify, quantify and analyze the

impact of water harvesting techniquesا on ecosystem services ranging

from hydrology functions, nutrient cycling, biomass production and

maintenance of semi-arid ecosystem, and biodiversity conservation to

food security, water availability and income generation.

2-Classification of water harvesting techniques

Runoff may be harvested from-roofs, ground surface and

intermittent or ephemeral water courses. Water harvesting techniques

which harvest runoff from roofs and ground surfaces fall under the

term rainwater harvesting while all systems which collect discharges

from water courses are grouped under the term floodwater harvesting.

Floodwater harvesting or floodwater farming often referred to as

water spreading and sometime spate irrigation (FAO,

1991).Classification of water harvesting techniques is varied as its

terminology (Pacey and Cullies 1986). Matlock and Dutt (1986)


82

classified water harvesting according to the form of runoff into water

spreading, diversion and micro catchment. A general and practical

classification has been established by the World Bank (1984) in sub-

Sahara study (Table1).��

��

��

��

��

� �

��

��

��

��

��

��

��

��

��

��

��

� �

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

�

��

��

��

��

��

��

��

��

��

��!��

��

��

��

��

��

��

��

��"��

��

��

��

��

#��

��

��

��

��

��$�%

&

��

��

��

��

��

��

��

'��

��

��

��

��

��

��

��

� ��

�

��

�

��

��

��

��


83

��

��

��"��

��

(��

��)��

��*

��

��

��

��

��

��

��!

��

��

��

��

��

��

��

�

+��

��

��

��

��

��

��

��

��

��

��

��

�

��

��

��

��

��

��

��

��

��

��

��

��

��(��

��

��

��

��

��

��

��%!$�

�,�

��

��

��

�

��

��

��

��

��

� �

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��-

(�.��

��

��

��.��

��

��

��

� ��

��

��

��

��

��

��

��


84

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��"��

#�/�

��

��

��

��

��

��

��

��

��

��

��

�0��

��

� �

��

��

��

��

��

�

��

��

��

)��

��

��*

��

�

��

��

��

��

��

��

��

��

/��

��

��

��

��

��

��

��

��

��

#�/�

��

��

��

��

��

��

��

�

��

��

��

��%$�

,$�

��

��

��1��

��

�2

3��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

4��

��

��

��

��

��


85

5��

��(-

6��

�78�

��

/��-

��

��

��

��

��

�

��

��

��

��

��

��

��

��

��

��

3��

��

��

��

��

��

��

��

��

7��

�78�

��

#��

��

��

��

��

��

��

��

��

��

�

��

��

��

��-

6��

��

��

��

��

��

��

��

MTSS = Micro catchments technique short slope.

ECLS = External catchments long slope.

FWHT= Floodwater harvesting technique.

Source:-World Bank (1984).


86

3-Types of water harvesting techniques

3-1 Surface harvesting system

This system catches rapid runoff from natural or man-made

surfaces and stored and often used for agriculture or domestic use.

They can be built whenever the landscape has characteristics which

produce large quantities of runoff from rainstorm on a regular basis

e.g. rock catchments, excavated reservoirs and earthen dams. The

main aim of such works is to conduct the sheet runoff onto restricted

area by limiting the area which receives the runoff and the amount of

water given per surface unit is increased.

a- Runoff farming systems

Runoff farming is a water harvesting system especially designed to

furnish water for growing crops. Runoff farming systems are not used

for drinking water and their main aim is to control runoff water in an

agriculturally productive manner, raising infiltration and improving soil

moisture conditions for crop growth. At the same time, this prevents

soil erosion by reducing runoff volume and velocity. Runoff farming

stabilizes soils, increases soil moisture and therefore increases crop

production. There are ranges of different runoff farming system, some

collect and concentrate water within the confines of a single field and

others collect water from external catchments and divert water from

streams or drains onto adjacent field.

b- Direct water system (Micro catchment)

A micro catchment consists of small prepared runoff collector

area directly upslope of the growing area. The runoff flows a short


87

distance to the infiltration crop growing area. The runoff water is

stored in the soil profile of the crop growing area during the

precipitation event. Runoff to run on area ratios vary from 1:1 to 20:1

depending upon the quantity of water which can be collected and

infiltrate into the soil profile. Micro catchment systems are relatively

effective in collecting water during precipitation events because of

their relatively small size and they are used in growing trees and

shrubs.

c- Supplementary water system

The runoff or the collected water is stored off site in some

reservoirs or storage container and applied later to the crop area with

some form of irrigation system. These systems have the advantage of

being able to supply the water received on the crop growing area

during the rainfall. They have extra costs associated with providing

the water storage and irrigation facilities. If the catchments or storage

facility are located above or upslope of the cropping area, a simple

gravity furrow irrigation can be used as an effective means of

applying the stored water. Drip and trickle irrigation systems have

been used and they have a high water application efficiency but are

expensive to install.

d- Combination system

The runoff water flows to the crop area where some water will

infiltrate into the soil profile and the excess water flows into a storage

facility for later application to the crop through some form of

irrigation system. A typical system may have the land shaped into


88

large ridges 5 to 10% side slope, and furrows on a 0.5 to 1% gradient

down the furrow. The plants are grown in the bottom of the furrow.

These systems known as eroded catchments and have been used with

trickle irrigation for crops and trees (FAO, 1994).

3-2 Underground harvesting system

These systems exploit water already infiltrated and concentrated

through natural hydrological processes into the soil. They comprise

sub-surface and raised sand dams. These systems provide a large

concentrated source for communal use and the stored water quality is

generally high due to in filtering and purifying effect on sand through

which it flows towards the dam or well.

3-3Water spreading

It is known as the use of run-on areas. The soil type influences the

method in different ways and deep soil can absorb large amounts of

water. Clay soils have low infiltration rates and high moisture

capacity, so they are suitable for deep flooding with subsequent

cropping. Sandy soils have quick infiltration and low storage and it is

suitable for the diversion. The Mediterranean climate which has low

evaporation and winter rainfall of about 100 mm is suitable for runoff

farming. In tropical summer rainfall and high evaporation water

harvesting is useful in areas with more than 250 mm. When the rain

and the growing period do not coincide, it’s necessary to store water

for later use. If the rainfall and the growing period are the same,

several application of water is needed during crop growth. Water

spreading can be divided into:


89

a- Natural Runoff

There are many examples of traditional use of naturally occurring

runoff in areas where rain is not sufficient for growing crops. Natural

runoff describes use of natural or unimproved runoff.

Several tribes use floodwater farming in the south-west of North

America (FAO, 1983).In Arizona they use runoff from sandstone

outcrops to water alluvial soil (Billy, 1981). They collect the runoff by

leaving the upper part of the field unplanted or increasing the storage

by simple impounding dams. Crops like maize and melons are

cultivated and this system does not use large investment of labor and it

takes advantage of any favorable feature such as roads which act as a

collector drain. Kovda (1961) reported that the use of natural

occurring runoff in arid areas of the USSR and ''Kair'' farming is the

cropping on flood terraces where the soil moisture is partly the result

of surface flooding and "Khaki" farming in Turkmenistan where

runoff from mountains inundates gentle slopes in the plains. In

Ethiopia similar practice the flooded plains recede are cleared and

planted with maize and sorghum (Carr, 1979). In Kenya pastoral

community with annual rainfall of less than 200 mm cultivate small

patches of sorghum by local traditional conditions practicing runoff

farming (Hillman, 1980). Where the rainfall is sufficient for cropping

(500 mm) it may be possible to make use of run-on areas by

increasing cropping intensity. Conservation bench terraces, separate

rotations are used for natural runoff in Morocco.


90

b -Collected and diverted runoff

Collected runoff system describes schemes where there is some

element of manipulation or management of land or the runoff. In

terraced wadis and other management schemes in valley bottoms, man

sets to manage the land and the water. Some of the ancient Negev

valley floor cultivation systems used only spate runoff down the

valley depended on the collection of the runoff from surrounding hills.

Some methods for inducing runoff, collecting it in channels and

distributing it to various terraced fields. Stone-line conduits were used

to take the water down to the farms with minimum loss by infiltration

and evaporation (Evenari, et al. 1982). In North Africa and the Middle

East the starting point of this type of water harvesting lies on the

alluvium in filling wadi floors and the traditional cross- wadi walls in

Jordan, built of stones, are a typical example. The walls have height of

about 0.5- 1 m. The walls are permeable and have no separate

overflow structures. Farming valley bottoms is an ancient practice in

Tunisia in an area with 100-150 mm of rainfall. Rows of olive trees

are planted across the width of valley bottom near a minor barrage

which slows down the floods and result in deposition of silt with

terracing effect (Damagnez, 1979). In Mexico silt traps are used as a

form of inbeds flood water harvesting (UNEP, 1983). They are built

with stones in series in narrow valleys, gorges or gullies and they trap

water as well as sediment. They are built incrementally with the

accumulation of sediments. The structures are always kept some 25-

50 m apart in order to minimize water loss by overtopping. Sizes of


91

the silt traps vary 0.15 - 0. 7 m in height and 1.5 - 9 m in length. The

size of the fields varies enormously from less than 2 m square to about

4 hectares. In many places terraced wadi systems exist with

impermeable earth dams. The earth dams are cheaper to construct.

This type of terraced wadi system called "jessour" in Tunisia and

Jessour are the area to be cultivated and mainly practiced across wadis

and also constructed on slopes in 100 - 200 mm rainfall zones.

Another form of water spreading in USSR known as "Liman"

irrigation consists of contour ramparts a cross the slope and they are

large structures 2 m high and 4 m wide and drain holes are used to

pass and control water movement (Kovda, 1961) . In Pakistan runoff

diverted from springs, streams and melt water from snow and glaciers

onto terraced alluvial fans called Oasis.In Yemen the floodwater is

diverted onto terraces in area of 400-600 mm annual rainfall

(Damangnez, 1979). Level bench terraces are constructed on steep

slopes with rocks 2- 3 m high and the terraced field 2-10 m wide.

Runoff from mountains carried the terraces and stone-lined canals

carry the water down and sometimes with the canals running

underneath the terraces. A similar system called "Sayl" irrigation is

the diversion of floodwater out of wadis onto leveled terraces.In

Australia two approaches are used to make more efficient of the

runoff. First approach to encourage grass growth by retaining runoff

on the ridges using short contour furrow. The other approach to catch

the runoff in drains and lead it to be spread on land for fodder crops

and pastures (Cunningham, 1967).


92

c- Inundation methods

Inundation methods describe systems where floodwaters are

impounded and retained long enough to saturate the soil so that a crop

can be grown on moisture stored in the soil.

In Sudan simple systems are used known as "Teras" collect and

hold runoff on gently sloping land embankments. After the water has

soaked into the soil millet is planted. In the semi-arid region of Brazil

the government research organization has studied a similar method

and produced designs for the optimum shape and size of the bunds and

cropping of the stored moisture with variations in cropping pattern

depending upon the amount of rainfall and runoff stored. In Rajasthan

in areas of low rainfall the method has been more successful. Low

contour bunds 0.3 m high divide the land into strips are inundated

with flooding to depth of 0.2 m and when the rains ceases, the stored

water infiltrates and a winter crop is grown.In semi-arid areas of Bihar

and Uttar Paradesh large scale inundation schemes have been used for

water control and land management. There are thousand of "ahars"

covering about 800000 ha. Low earth bunds are built to retain runoff

and most ahars flood less than 500 ha but others more than 4000 ha

(Kolarkar, 1983). The soil must have enough depth and moisture

holding capacity and the crops are grown in winter. The volume of

water stored is less important than the area of the land which

submerged. The retaining is usually 3 m high and may extend several

kilometers on the contour. There is a waste-weir to serve as

emergency spillway. The spillway is required because of the danger of


93

heavy storm occurring when is full and ahars are usually built in a

series down the slope and the failure of any one would imperil those

lower down the slope. The crop is winter wheat planted as soon as the

flooded land has dried out. Sometimes subsidiary crop known as

floating rice is grown during the summer monsoon. This technique of

cultivation floating rice followed by a second crop after the water has

receded is also practiced in Thailand. A second advantage of this

system soils in semi-arid areas often have salinity and this is

controlled by leaching. The infiltration amount of water may have the

effect of raising the water table near the ahars with improvement of

the water supply in shallow wells. Inundation farming is used in

Rajastan (Kolarker, 1983). Earth bunds are built across the valley

plain to catch and store runoff and silt and these are called

submergence tanks or "Khadins". The tanks are designed in areas

where the annual rainfall is 165 mm and the catchment ratio of at least

15:1. The construction features are the same as ahars with emergency

spillway and sluices to release the water. Winter wheat crop is grown

or legume.Secondary benefits of most inundation systems are the

leaching of salinity by the stored water and the improvement to the

yield of wells down stream.

d- Flood diversion

Flood diversion systems concern with diversion and spreading of

floods and spate flows. Diversion of flood water from its channel

usually involves some forms of structure, a barrage or weir to divert

the water. Simple diversion constructed annually using stones, wire


94

netting, poles, brush wood and boulders and probably will be

destroyed by flash floods. The floods are also likely to damage the

conveyance channel unless it’s provided with safety devices to spill

water. The canal is excavated in the river bank so that the level of the

canal bed is higher than the bed level of the river. This system is

widely used in Sind province in Pakistan to collect water from the

river. Generally heavy deposition of sediments at the beginning of the

canal occurred and clearing is essential. Regulators are used for flood

water diversion out of its channel by raising the water level through

some form of weir or barrage and may be temporary or permanent

structures. Floodwater diversion techniques are those techniques

which force the water to leave its natural course. The water diverted

conveyed to allocations suitable for crop production and applied

through a system of channels, dams and bunds. A famous example of

flow diversion from ancient times in the great dam near Marib in

North Yemen (NAS, 1974). At present flood irrigation is practiced in

Marib by means of simple sandy diversion dams along the wadi.

Another ancient system is reported by UNEP (1983) from Northern

Mexico. Around 1000 AD an intricate system functioned in area with

rainfall 125-175 mm, incorporating diversion dams, canals, head gates

and bordered gardens and it was receiving water from many

catchments covering 4250 ha.

3-4 Developing ground waters

The sources of water storage are the spate flows in streams, rivers

and runoff stored in tanks and dams. The conditions required for


95

recharge includes adequate surface for infiltration, good water storage

capacity which defined as specific yield or the volume of water which

drains from the rock under gravity and hydraulic conductivity. Two

problems may occur of salinity and silting due to flash runoff which

usually carries a heavy sediment load which is likely to block the soil

surface and reduce infiltration and siltation tanks are commonly used

to reduce this problem. Recharge methods can either be carrying

runoff to an infiltration zone or seepage through the bottom of canal.

The exploitation of groundwater may offer a solution in arid

regions and shallow wells is a common way of using groundwater. In

India a common design is stone-lined circular wells and this

traditional method has been successfully operated for centuries and

the water is lifted by hand or ox-power for domestic use and

irrigation. Boreholes equipped with hand pumps, hand-dug wells and

horizontal wells are used in many countries. A modern development

of the age-old system of driving a horizontal shaft into the side of a

hill until it reaches the water table and the water flow out through

tunnel under gravity. This method is widespread in North Africa

`foggaras` and in Iran `ganats` and in Afghanistan and Pakistan they

are called `Karezes`. The danger of ecological damage resulting from

the over exploiting of groundwater particularly fossil water which can

not be replaced.

3-5 Floodwater development

In dry land countries with ephemeral water courses (wadis),

significant improvement to runoff farming can be achieved through


96

spreading and retention of floodwaters for a finite duration to permit

infiltration. In order to implement this concept a system of structures

will be required to increase infiltration and retention time, thereby

slowing down and reducing the runoff velocity. The following

functional applications of detention, dispersion and diversion

structures are used.Detention structures are built of locally available

material (soil, gravel, stone, boulder, and rock). The height of these

structures is usually less than 10 meter across wadis or valleys for

slowing down and retaining floodwater and healing gullies. They are

suitable where relatively deep wadi course with gently sloping valleys

are becoming gullied. A detention dam would be designed to specific

height to retain temporarily a large portion of the maximum flow, thus

allowing recharge of the alluvium upstream. Due to constant crest

elevation distribution of flow by dispersion uniformly through area

will be achieved for increasing the soil moisture both upstream and

downstream of the dam. During long- term operation, the wadi main

channel and flood plain behind the dam would be filled with sediment.

Water diversion is the traditional way of using flash floods and it is

used to irrigate areas close to or within the water course. Three types

of water harvesting techniques may be practiced. Lateral diversion

technique consists of diverting apart of the floodwater from an

ephemeral water courses or a gully to a conveyance channel which

may provide water for cultivation downstream. This system has been

generally used in streams with deep steep bed slopes 5 to 10%. The

off- take is excavated in the stream bank and several off- takes can be


97

used to irrigate the same land.Earth dike diversion is an improved

version of the lateral diversion. The primary objectives is to provide

head for the off- take to irrigate greater areas. It’s used on streams

with relatively low bed slopes. Small retention dams practice is

usually encountered in the Saharan zone where floods are less

frequent and have limited runoff volumes. It consists of small earth or

loose rock dikes constructed across the river and designed to store

water for crop cultivation and to recharge groundwater.All these

techniques are subject to the natural damage and occasionally

washouts particularly for the diversion dams. It need cleaning of the

sediment deposited upstream the dikes. Their reconstruction and

maintenance require a tremendous effort in terms of labor and may be

a way of promoting solidarity within the community.

4-Results

Semi-arid areas in Africa face climatic variability at different

temporal scales. Higher natural inter-annual climatic variability is

expressed as drought and floods; a high seasonal variability leads to

dry spells. Farmers in semi-arid zones have therefore developed

strategies including rainwater harvesting techniques e.g.

supplementary irrigation to cope with this uncertain and erratic

rainfall patterns. Rainwater harvesting practices refer to practices

whereby rainwater is collected artificially to make it available for

cropping or domestic purposes.


98

4-1Water harvesting in relation to crop production

The main factors determining the magnitude of runoff in the

catchments area are the rainfall characteristics, soil and topography. In

larger catchments runoff has to cover longer distances, implying a

longer retention time. Micro catchments response rapidly to rain by

generating small amounts of runoff and do not create erosion

problems (Boers et al. 1986). Macro catchments produce runoff less

frequently than micro catchments and at larger volumes with addition

of erosion hazard. Crops considered for growth under runoff

conditions should be screened for high and resilient food, fodder and

firewood production and for shrubs and trees. They should tolerate

periods of prolonged droughts, salinity and water logging.

Leguminous species are of particular interest as they improve the

nitrogen status of the soil. Water requirement of annual crops is

generally less than crops like shrubs and trees. The different runoff

systems impose various growing conditions like the amount of runoff,

event, the depth of infiltration and the catchments size. Crop selection

and associated water use are strongly linked to the type of runoff

system applied.

Water harvesting helps crops by providing extra moisture at

different stages of growth. Periods of extra moisture of significant

differences are around sowing time when germination and

establishment can be improved, during a mid season dry spell when a

crop can be supported until the next rains and while the crop is at the

vital stages of flowering and grain fill. The most common cereal crops


99

grown under water harvesting are sorghum, pearl millet and maize.

Sorghum is most common grain crop under water harvesting systems.

It is a crop of dry areas, drought resistant, tolerate water logging and

used in parts of East and Southern Africa as a food grain. For high

production rainfall of 450-650 mm is needed but satisfactory crop can

be obtained with about 300-380 mm (ILO, 1999).The selection and

testing of alternative crop varieties and the selection and breeding

cultivars for semi-arid regions are promising. Some varieties adjust

their growth habit according to the available moisture by tillers when

moisture is available or going dormant when the moisture is short or

only carrying through to ripening a proportion of the seed heads

available.

4-2Water harvesting techniques adapted in North Darfur State

Several water harvesting techniques were practiced (Reij et al.

1986; Mohammed, 2000). Farmers adopted bench terracing system for

many thousand years ago, the signs of which are still found in hilly

areas such as Jebel Marra (HTS, 1958). Spore (1997) noted that

"Water harvesting techniques was developed by the ancient"

Nabateans" over 3000 years ago in Jordan and it is probably not a

coincidence that very similar technique have been developed and have

survived in the Red Sea Hills of North East Sudan and in the Central

Darfur region). Teras technique is a more common practice all over

the state. Teras is a piece of arable land bounded on three sides to

capture runoff from adjacent catchments. It is a small scale privately

managed and is built in earth structures and used for subsistence crop


100

production. It aims at water harvesting and moisture conservation

beside nutrient harvesting and erosion control (Mohammed, 1994).

Dams up to 4 m high provided with concrete lined or masonry

spillways and sometimes with bottom outlets retain floodwater from

the wadi for a few months (ILO, 1999). Small earth dams are the most

common type and they require some care in design, construction and

regular maintenance. Supplementary irrigation is practiced in Sag El

Naam project (Mohammed, 1994).Flood diversion is practiced in

Kidinir area using a canal for diverting wadai flows to 8 km and

annually 2000 ha are being irrigated. Spread irrigation systems like

hafirs for collection of floodwater surrounded by embankment, with

siphon inlet provided with sluice gate and off-spreading were

practiced along the wadis. In Malam El Wadayin project the storage

water in the dam was diverted by two canals to irrigate 300

ha(Abdalla,2008). Flood irrigation systems consist of small earth

dams generally 'U' shaped with upward opening for the retention of

rainwater. Small embankments about 2 m high for the delimitation of

impounding reservoirs and the water diverted from the wadi during

floods. The main limiting factors of crop production in North Darfur

State are water shortage, lack of inputs, techniques and marketing.

The use of water harvesting techniques can shift millet and sorghum

cultivation from the impoverished sands to the clay soils along wadis

beds. Areas having characteristics of the flat valley along wadis near

Al Fashir are approximately 100000 ha. These areas have adequate

exploitable discharge of wadi runoff, slight and uniform slopes, soils


101

with good permeability, and absence of chemical anomalies and

coarse texture. Different water harvesting techniques of micro

catchments, water spreading and floodwater farming exist. Use of

water harvesting techniques will increase food, fuel wood and forage

production and rehabilitate the sandy soils and control land

degradation and combat desertification.

5- Discussion

African dry lands are affected by climate change. It was

confirmed temperature increases for most of Africa, while expected

rainfall tends vary and the climatic variability will increase, leading to

an increase in droughts and floods and growing uncertainty about the

on set of the rainy season. In the context of agricultural production in

African dry lands soil and water conservation practices such as

rainwater harvesting provide an opportunity to stabilize agricultural

landscapes in semi-arid regions and make them more productive.

Water harvesting is the most common soil and water conservation

techniques is massively promoted by farmers, extension services and

government agencies (Stroosnijder, 2003). Rain water harvesting

techniques are generally considered to be only beneficial in this

respect but the main problems are low rates of adoption (Tabor, 1995;

Bodnar and de Graaff, 2003) or failed adoption processes due to lack

of participation by farmer .Rainwater harvesting practices have an

overall positive effect on landscape functions and hydrological

improvement concerns the recharge of aquifers and increase in soil

water. Rain water harvesting systems aim to minimize seasonal


102

variation in water availability such as droughts and dry spells

(Rockestrom et al., 2002).

6- Conclusion

Rainwater harvesting are mostly simple and there are more space

for technical improvement. Crop yields are higher when water

spreading techniques were applied and reduce crop failure during dry

spells, droughts and thus help to enhance food security .The adoption

of techniques proved to have positive effect to increase farmer’s

income. The major challenges lie in improving nutrient management

through mulching, animal traction and the traditional practices may be

combined. For more in-depth research is required at local scales. The

socio-economic conditions are qualitatively known (Oweis, et al.

1999) but not applied quantitatively to understand and support the

individual decisions of farmers. Crop and risk assessment models and

approaches must be developed so far rainwater harvesting techniques

(Young et al., 2002) rely mainly on ecological and technical

information. Economic, social and cultural factors are not combined

for access to markets and labor.

REFERENCES

1. Abdalla, S.A. (2008). Use of controlled spate irrigation for the

improvement of sorghum growth and productivity in North

Darfur State. Ph.D. Thesis, University of Khartoum.

2. Billy, B. (1981). Water harvesting for dry land and floodwater

farming on the Navajo Indian Reservation 3–7. In: Rainfall

Collection for Agriculture in Arid and Semi – arid


103

Regions.Dutt, G.R.; Hutchinson, C.F. and Garduno, A. (Eds).

Workshop at Tucson Arizona, USA. Pub. By

Commonwealth Agri-Bureau, Farnham Royal,Bucks. UK.

3. Boers, T.M., Graaf, M. dc. Febbs, R.A. and Ben Asher, J.

(1986). A linear regression model combined with a soil water

balance model to design micro–catchments for water harvesting

in arid regions. Agricultural Water Management 12: 21–39

4. Bodnar, F.,de Graaff,J., 2003. Factors influencing adoption of

soil and water conservation in Southern Mali. Land Degraded.

Deevelop,14,515-525.

5. Carr, M.K.V. (1979). Land use and irrigated agriculture in the

Woito and Lower Omo river valleys. UNDP/FAO Project E T

H /78 /013 Development of Irrigated / Agriculture.

6. Cunningham, G.M. (1967). Furrow aids revegetation at Cobar

despite the worst drought on record. J. Soil Water Conservation

of N. S.W. 23 (3): 192-202.

7. Damagnez, J. (1979).Mediterranean climate, the economic use

of water, and crop production. In: Soils in Mediterranean Type

Climates and their Yield Potential, PP 43- 55- Proc. 14h coll

Int. Potash Inst. Berne, Switzerland.

8. Evenari, M. L., Shanan, L. and Tadmor, N. (1982). The

Negev: The challenge of the desert, Harvard University Press,

Cambridge.

9. FAO (1983). Field measurement of soil erosion and runoff.

FAO Soils Bulletin No. 69. FAO, Rome.


104

10. FAO (1994). Water for improved agricultural production.

Proceedings of the FAO Expert Consultation, Cairo, Egypt, 21–

25 November 1993. Water Report No. 3. FAO, Rome.

11. FAO (1991). Network on erosion. Induced loss in Soil

Productivity. FAO, Rome.

12. Hillman, F. (1980). Water harvesting in Turkana district,

Kenya. Pastoral Network Paper 10 d. ODI, London.

13. HTS. (1958). Jebel Marra investigations. Report in Phase I

Studies.

14. ILO (1999). The effects of the projects components on the

environment.El Fashir and El Obied Districts, Darfur and

Northern Kordufan.

15. Kolarkar, A. S.,Murthy, K. N. K., and Singh, N. (1983). “

Khadin - A method of harvesting water for agriculture in the

Thar Desert, Journal of Arid Environments, 6,pp 59. 66,

London.

16. Kovda, V. A. (1961). Land use development in the arid regions

of the Russian plain, the Caucause, and Central Asia. In: A

history of land use in arid regions. Arid Zone Research Vol

XVII. UNESCO, Paris.

17. Matlock, W. G. and Dutt, G. R. (1986). A primer on water

harvesting and runoff farming. College of Agriculture,

University of Arizona. Irrigation and Water Management

Institute.


105

18. Mohamed, Y. A. (1994). Traditional water harvesting

Techniques and their contribution to food security: case study

of Wadda Village, North Darfur, Sudan. In: M. M. M. Ahmed

(Ed), Indigenous knowledge for sustainable development in the

Sudan. Khartoum University Press, Khartoum, Sudan, 178–

214.

19. Mohamed, A. A. (2000). Water harvesting for crop production.

Ph. D, Thesis, University of Khartoum.

20. NAS (1974). More water for Arid Lands. Promising

Technology and Research Opportunities.Washington, D.C

21.Oweis, T.,Hachum,A., Kijne, J.( 1999). Water Harvesting and

Supplemental Irrigation for Improved Water Use Efficiency in

Dry Areas. International Water Management Institute,

Colombo, Sri Lanka, pp .1-51.

22. Pacey.A.with Cullis, A. (1986). Rainwater Harvesting. The

Collection of Rainfall and Runoff in Rural Areas. Intermediate

Technology Publications, London, UK.

23. Reij,C.; Turner, S.D. and Kuhman, T. (1986). Soil and water

conservation in Sub-Saharan Africa: Issues and options, IFAD,

Rome/CDCS, Amsterdam.

24.Rockstrom, J.,Barron, J.,Fox, P.( 2002). Rainwater

management for increased productivity among small-holder

farmers in drought prone environments. Phys.Chem. Earth 27,

949-959

25. Spore. (1997). More crops with less water. Spore No. 70, P. 5.


106

26. Stroonijder, L.(2003). Technologies for improvising rainwater

use efficiency in semi-arid Africa. In: Proceeding of the

symposium and Workshop on water conservation Technologies

for Sustainable Dry land Agriculture in Sub-Saharan Africa,

Bloemfontein, South Africa, and April 8 – 11 2003. Pretoria,

South Africa .ARC- Institute for Soil, Climate and Water,

pp.60-74.

27.Tabor,J.A.(1995). Improving crop yields in the Sahel by

means of water harvesting. J. Arid Environ. 30, 83-106.

28. UNFP (1983). Rain and storm water harvesting in rural areas:

Ed. UNEP Tycooly International, Dublin, Ireland.

29. World Bank (1984). Towards sustainable development in Sub-

Saharan Africa. Washington DC: The World Bank2.

30. Young. M.D.B., Growing, J.W., Wyseure, G.C.L., Hatibu,

N.(2002). Parched- thirst:Development and validation of a

process- based model of rainwater harvesting .Agricultural

Water Management 55,121-140.

Eng6

Education

Transcript of Eng6