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Technologies for water harvesting and soil moisture conservation in small watersheds for small-scale irrigation, R.K. Sivanappan

R. K. Sivanappan
Saivy Pumps Ltd., Coimbatore India

Conceptual approach
Appropriate structures and their functions
Construction procedures
Planning concept, design and construction of these structures
Performance assessment and lessons learned
Appendix 1 Examples of design of check dam, percolation ponds and tanks

Water is essential for all life and is used in many different ways - for food production, drinking and domestic uses and industrial use. It is also part of the larger ecosystem on which bio diversity depends. Precipitation, converted to soil and groundwater and thus accessible to vegetation and people, is the dominant pre-condition for biomass production and social development in drylands. The amount of available water is equivalent to the water moving through the landscape. It also fluctuates between the wet and dry periods. Fresh water scarcity is not limited to the arid climatic regions only. Even in areas with good supply, the access to safe water is becoming a critical problem. Lack of water is caused by low water storage capacity, low infiltration capacity, large inter-annual and annual fluctuations of precipitation and high evaporative demand.

Irrigation in Africa is a privilege since, the cost of providing irrigation to one hectare could be as high as US$ 20 000/ha and therefore cannot be implemented. Even for small-scale irrigation using groundwater, well (both open and tube well) construction is costly. It may amount to more than US$ 10 000 to provide irrigation water for one hectare of land.

Irrigation potential which exists in South and East African countries is much more than the presently irrigated area. The geographical area, irrigated area at present and irrigation potential for selected countries are given in Table 1. The table indicates the possibilities of bringing a larger area under irrigation in these countries for food security.

A variety of essential soil moisture and water conservation technologies must be adopted to reduce the cost of irrigation, extend it throughout and promote sustainable small-scale irrigation on a watershed basis. These technologies are essential especially in drought-prone areas. Even though drought is a purely natural calamity caused by the failure of (monsoon) rain, it can be minimized by careful planning and operation. During good rainy years, excess rainwater should be stored in the soil and also underground using suitable soil moisture conservation measures and water harvesting structures on a watershed basis. This stored water can subsequently be used for irrigation.

Conceptual approach

Watershed development and management implies an integration of technologies within the natural boundary of a drainage area for optimum development of land, water and plant resources, to meet the people's basic needs in a sustained manner. A watershed is an area from which runoff resulting from precipitation flows past a single point into a large stream, river, lake or pond. Each watershed is an independent hydrological unit. It has become an acceptable unit of planning for optimum use and conservation of soil and water resources.

TABLE 1 Area, population, irrigation details of selected countries







Area (M ha)






Population (Million)






Rainfall (mm)






Cultivable area (M ha)






Cultivated area (M ha)






Irrigation Potential (M ha)






Irrigated area (M ha)






Population per sq km






The concept of integrated watershed development refers to the development and management of the resources in the watershed to achieve higher sustainable production without deterioration in the resource base and any ecological imbalances. This concept requires the formulation and implementation of a package of programmes with activities for optimum resource use in the watershed without adversely affecting the soil and water base or life supporting system. The concept assumes more importance in the context of planning for sustained development. Watershed development aims at preventing watershed degradation resulting from the interaction of physiographic features. It eliminates unscientific land use, inappropriate cropping patterns and soil erosion, thereby improving and sustaining productivity of resources leading to higher income and living standards for the inhabitants in the watershed area. It therefore involves restoration of the ecosystem, protecting and utilizing the locally available resources within a watershed to achieve sustainable development.

Rainfall failure occurs once every 3 to 5 years and is usually below 50% of the average annual rainfall of the region. During periods of rainfall failure, the groundwater level lowers since fluctuations in the water table levels depend on the rainfall when both surface and groundwater availability becomes critical. Drought begins to prevail and there is difficulty to cope up with the water demand during this period. Similarly, in some locations or areas water shortage is observed just before the rainy season commences. These two situations can be managed if suitable soil and moisture conservation measures are systematically implemented on a small watershed basis.

There are always strong links between soil conservation and water conservation measures. Many actions are directed primarily to one or the other, but most contain an element of both. Reduction of surface runoff can be achieved by constructing suitable structures or by changes in land management. Further, this reduction of surface runoff will increase infiltration and help in water conservation.

Appropriate structures and their functions

To increase the period of water availability and overcome water scarcity in drought years, the following activities can be implemented in the field for a compact, viable watershed of about 200 - 500 ha.

Soil and water conservation can be approached through agronomic and engineering procedures. Agronomic measures include contour farming, off season tillage, deep tillage, mulching and providing vegetative barriers on the contour. These measures mainly prevent soil erosion but will also help in improving soil moisture availability in the watershed.

FIGURE 1 Soil and water conservation measures on a watershed basis

The engineering measures adopted differ with location, slope of the land, soil type, amount and intensity of rainfall. Depending on these parameters, the methods commonly used are contour trenching, contour stone walls, construction of temporary and permanent check dams and gully plugging structures. Additionally, percolation ponds, silt detention tanks and irrigation tanks are constructed to harvest water and recharge it to the groundwater for use in agriculture (irrigation). Farm ponds can also be constructed for every 4-5 ha in the watershed to provide protective/supplemental irrigation.

The above soil and water conservation management and water harvesting programme should be implemented in an integrated manner on a catchment/watershed basis (Figure 1).

Functions of the structures

Contour bunds, contour barriers (vegetative and stone), contour trenches and contour stone walls will not only prevent soil erosion but also obstruct the flow of runoff water. Consequently, the obstructed water will increase the soil moisture and recharge the groundwater in the area.

Check dams: This may be a temporary structure constructed with locally available materials. The various types are: Brush wood dam, loose rock dam and woven wire dam. The main function of the check dam is to impede the soil and water removed from the watershed. This structure is cheap, but lasts about 2-5 years. The cost of the structure is about US$ 200 - 400 depending on the materials used, the size of the gully and the height of the obstruction (dam). A permanent check dam can be constructed using stones, bricks and cement. Small earth work is also needed on both sides. Costs vary from US$ 1 000 - 3 000 depending upon the length and height of the dam. A little water is also stored above the dam. This water recharges the groundwater.

Percolation Pond: The percolation pond is a multipurpose conservation structure depending on its location and size. It stores water for livestock and recharges the groundwater. It is constructed by excavating a depression, forming a small reservoir or by constructing an embankment in a natural ravine or gully to form an impounded type of reservoir. The cost of this type of structure is estimated at around US$ 5 000 - 10 000. The capacity of these ponds or tanks varies from 0.3 to 0.5 mcft (10 000 - 15 000 m3). Normally 2 or 3 fillings are expected in a year (season) and hence the amount of water available in one year in such a tank is about 1 mcft to 1.5 mcft (30 000 - 45 000 m3). The cost for one mcft (30 000 m3) varies from US$5 000 to 15 000. This quantity of water, if it is used for irrigation, is sufficient to irrigate 4-6 hectares of irrigated dry crops (maize, cotton, pulse, etc.) and 2-3 hectares of paddy crop.

Irrigation Tank: The main function of this storage structure is irrigating crops. It is constructed below the above-mentioned structures in a watershed. In Tamil Nadu, India, each tank irrigates from 10 to 5 000 hectares. In south India, there are about 2 000 000 tanks, irrigating about 3.5 million hectares. Earthen bunds are reinforced with masonry to collect and store rainwater for irrigation. The cost of this tank (dam) depends upon the size, location and site condition. It costs about US$ 1 500 - 2 500 to irrigate 1 ha of land. Water from the tanks is normally used to grow paddy crop.

Apart from the above, to increase moisture availability to agricultural and tree crops, in situ moisture conservation techniques must be adopted in addition to the large scale soil and moisture conservation and water harvesting structures in the watershed.

The following are some of the in situ moisture conservation measures which can be practised in the watershed to increase production.

For agricultural crops, the measures adopted are forming ridges and furrows, broad bed and furrows, basins, tie ridging (random tie ridges) and water spreading.

For tree crops micro catchment, saucer basin, semi-circular bund, crescent shaped bunds, V ditch technology, catch pits and deep pitting can be practised.

In addition to the above measures and structures, small storage structures with a water storage capacity for an area of about 0.4 to 0.5 ha can be constructed in large numbers one for every 10 to 20 ha catchment or watershed at the foot hills slopes and hilly areas. These storage facilities would attenuate the floods during storms. These measures will also ensure soil moisture for good growth of trees grown down stream recharging the groundwater in the region and making available more water for drinking and irrigation water.

Construction procedures

The procedure for the construction of tanks and check dams, on a watershed basis, is as follows. Detailed studies are first made of the watershed to determine its current erosion condition, land use and water balance condition. Based on these data, decisions are made on the construction of check dams (temporary/permanent), percolation tanks and irrigation tanks (refer to Figure 1). The community in the watershed should be involved in planning and selecting the type of structures and locations of the structures. If a large quantity of water is lost through runoff from the watershed, 2-3 percolation tanks or one irrigation tank can be planned based on water availability. A number of check dams can be provided to arrest erosion and to plug the gullies in the rivulets at appropriate places.

The construction can be done using human labour if necessary or by a mix of mechanical and human effort. In India, these works are mostly executed by labourers to give employment to the village people. Only 10% of the work is done mechanically (bulldozer) i.e., digging the foundation and excavating earth to form bunds. Otherwise 80-90% of the work can be done by machines, if employment is not a criterion.

The cost of construction of the above-mentioned structures depends upon the soil type, the size of the tank and season of construction. The proportions of earth and masonry works for the three different structures are as follows.

Type of structures

Earthwork (%)

Masonry and concrete

Check dam



Percolation tanks and irrigation tanks



The average costs of construction of percolation ponds are as follows: (actuals taken from the estimates)

Type of construction


Capacity of the tank (mcft)

Earthwork cost in US$

Material cost in US$

Cost/Unit (1 mcft or 30 000 m3)

Percolation pond 1

90 %


4 000


10 000

Percolation pond 2

93 %


4 200


10 000

Percolation pond 3

70 %


2 000

4 500

25 000

Percolation pond 4

77 %


2 000

5 000

28 000

Percolation pond 5

75 %


2 000

3 000

25 000

The actual construction is undertaken when the community is free from agricultural work and the works are spaced in such a manner that the construction will be completed before the rain (monsoon) commences, so that the structure will be used immediately. Small structures are completed within 2-3 months while a large one takes about 7-9 months.

These tanks or dams are constructed by Government without the involvement of people during construction. The maintenance is normally not done but is the responsibility of the Government. If the people are involved in constructing the structure they feel ownership and will take responsibility for maintenance. Since the work is given to the contractors the quality of the construction is also questionable. Wherever the community is involved in the construction, they undertake the maintenance of the structure themselves.

Users' (farmers') participation

The efficiency of a tank or pond depends on the organization of its beneficiaries. This organization of beneficiaries are required for each and every tank, especially for maintenance and rehabilitation. The role of the water users' association (WUA) or farmers' organization (FO) in general is as follows.

· Planning including selection of site.
· Construction.
· Distribution of water in irrigation tanks.
· Maintenance of the structures.
· Mobilization of resources for the work, management and maintenance.
· Involving themselves in the work.
· Resolution of the conflicts.

Linkages should be established between the farmers and various organizations. The NGOs are required as a catalyst and to create awareness among the farmers about efficient utilization of the resources.

It is said that users' participation is necessary for better utilization and management of the resources. In practice this participation is very difficult to achieve. To some extent farmers' participation in the management and utilization of irrigation tanks is forthcoming. However, involving farmers is not such an easy task with check dams and percolation ponds, since there is no direct benefit to the farmers as in the case of irrigation tank.

Involvement of farmers in system management and project management from planning to operation and management of the system should be stressed. Coordination among the association members has to be intensified for proper guidance.

Planning concept, design and construction of these structures

When selecting the construction site of check dams, percolation ponds and tanks, the following criteria can be considered.

Check dams: This is constructed across rivulets and gullies to control erosion, prevent gully formation and to arrest the flow of water to allow it to go underground. A number of such obstructions will be useful for soil and moisture conservation measures. Inexpensive, temporary structures can be constructed using vegetation, stone or brushwood, available at the site. Large numbers can be provided to reduce erosion and formation of gullies. Permanent check dams can be located at the junction of one or two streams or gullies using masonry structures.

Percolation ponds: The following factors may be considered:

· It should not be located in heavy soils or soils with impervious strata, otherwise the top soil should be porous.

· Suitable and adequate soil should be available for forming embankments.

· The ideal location of the pond will be on a narrow stream with high ground on either side of the stream.

· Simple, economic and efficient surplus arrangement should be possible.

Pond size should be decided on the basis of the catchment area and the number of fillings possible for the pond in the area.

Irrigation tanks: The location should be such that it should receive water from a large catchment area.

· There should be land below the site suitable for irrigation.

· Cooperation and coordination of the farmers and the community is essential to use the water.

· The location should be such that it will be a narrow point with high ground and wide open space in front of the tank location so that a large quantity can be stored with minimum cost.

A model design of a percolation pond/tank and check dam is given in Appendix 1.

After the plan and estimates are prepared and approved by the appropriate authority, construction can be entrusted to village people (beneficiaries) in case of check dams or percolation tanks and to the WUA and/or FO in case of irrigation tanks. Not much operation and management is needed in the case of check dams and percolation tanks but irrigation tanks must be visited regularly to release water and conduct repairs and maintenance. The WUA or FO can be involved from the time of construction, operation of the system and maintenance of the structure.

Performance assessment and lessons learned

Farmers should always be involved in planning and executing field programmes. Management and new techniques should not become a continuous burden to the farmers. The design and implementation of a conservation and rehabilitation programme is likely to be most successful, if they are the product of interdisciplinary work between technical staff and those experienced in economic and social issues.

Based on the above background, the author had an opportunity to study many projects implemented by NGOs, government departments and farmers on water harvesting and soil moisture conservation in small watersheds in India. After visiting all the projects and following discussions with the people concerned, the following assessments were made about their projects and the lessons learned from the experiences.

In one village, owing to the inspiration of a dedicated NGO, the village has dramatically improved after the villagers executed all the development work including soil conservation and water harvesting works. Though the annual rainfall was only 450 - 500 mm, the groundwater table was maintained at a depth of 6 -7 m and there is no water scarcity even during drought years in that village. The farmers are using drip irrigation for widely spaced fruit and orchard crops and are planting trees in barren and common lands.

In another large project (40 000 ha) funded by the World Bank, soil and water conservation and water harvesting measures were conducted on a watershed basis. Though it was a Government project it was implemented with the help and involvement of the community from the planning stage to execution. Consequently the project achieved its goal. The farmers obtained 150 - 200% more yield. The groundwater table in the watershed was raised and the community had no difficulty to get water. At the same time, another project failed and expected results were not been achieved because farmers were not involved. Therefore it is clear that water availability can be increased if soil conservation and water harvesting measures are implemented on a watershed basis involving the community. In addition more water will be available for small-scale irrigation, which will assist in improving the people's living conditions and food security in the coming years.

Appendix 1 Examples of design of check dam, percolation ponds and tanks

The design procedure for the check dam (permanent), percolation tank and irrigation tank is more or less the same.

In all three cases, the weir length (surplus weir) has to be designed and/or calculated.

In the case of percolation tanks and irrigation tanks, the capacity of the tank has to be calculated on the basis of the rainfall and catchment area of the tank. For check dam, this is not necessary.

The method of calculating the weir length and the capacity are the same in all cases. The procedure is as follows:

· select the site for the tank or check dam.

· from the Topo sheet or village map, find out the correct catchment area of the watershed at that location.

· take the cross sections and longitudinal section of the stream or gully where the tank or dam is constructed.

· based on the levels taken, prepare 50 cm contour for sufficient area to decide the water spread area and the capacity of the tank based on the yield of the watershed.


Catchment area

- 40 ha

Monsoon/Rainfall season

- 625 mm

Yield from catchment assuming the catchment is good (more yield) tables are available.

- 51 480 m3

Capacity may be designed as 1/3 of the yield from the catchment i.e.

- 17 000 m3

Deciding full tank level (FTL), Maximum water level (MWL) and tank bund level (TBL):

From the levels taken, draw the contour lines at every 50 cm interval between the bed level and the highest ground level at the site. From these contour lines, the capacity of the tank at 0.5 m, 1.0 m, 1.5 m and 2.0 m height above the bed level is calculated. The contour (level) at which the tank can store 1/3 of 51 400 m3 i.e. 17 000 m3 is the required height of the weir. That is called full tank level (FTL). For small tanks, the height of flow over weir is taken between 0.30 - 0.60 m and this level is known as maximum water level (MWL). The tank bund level (TBL) is calculated by adding 1m or more based on the height of the water stored above the bed level of the tank.

Design of weir:

Maximum Discharge Q = CIA/360


Q= Discharge in cumec

I = Intensity of rainfall (25 mm/hour)

A = Area of catchment in ha.

To decide the length of the weir


= CLH3/2

=1.67 LH3/2 (broad crested weir C = 1.67)


= Q/CLH3/2 = CIA/360 CLH3/2


C = Constant =1.67

L = Length of the weir

H = Flow height over weir

After deciding the length of the weir (L), other structural calculations may be made, including the body wall, wing walls and apron. Finally the stability of the structure is checked.

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