5.2 Traditional methods of soil and water conservation - coconut pick-ups, India

Introduction

"Coconut pick-ups" is the term popularly used to describe diversion weirs constructed exclusively to benefit coconut gardens. The "pick-ups" are small structures built across seasonal or perennial streams to slow the flow of water at appropriate locations. This results in surface water storage, groundwater recharge, reduction of soil loss due to erosion, and provision of water for other activities. The technical concept is simple; i.e., to slow the flow of water at strategic places in order to collect water using bunds constructed of locally available materials, like stones, boulders or clay (mud). Mud bunds are turfed with a specific variety of locally available grass, Maane hullu. The bunds are usually built within an incised stream bed almost to the height of ground level, depending upon the width and steepness of the stream. During periods of peak stream flows, the berm creates an hydraulic obstruction which backs up the water, flooding the coconut plantations located on either side of the stream. The water impounded in this manner generally recedes within 3 to 4 days. In addition to supplying the plantations with water, the flood leaves a few millimetres of silt, and associated major and micro nutrients and organic matter derived from manure, leaves and the mineral carried downstream, particularly during the early monsoonal flows. Excess water subsequently flows into a storage tank. Sometimes there will be several coconut pick-ups and tanks within a catchment, and excess flows may be conveyed from one tank to another.

This case study illustrates the utility of this technology by reference to a pick-up located in the Tumkur District of Karnataka. Tumkur District receives an average annual rainfall of 688.4 mm. The net irrigated farming area accounts for 13.8% of the net farming area, and extends over 77 673 ha., 361.7 ha of which are irrigated with water supplied from tanks. Tumkur District stands third in terms of the number of pick-ups in active use, after the Mandya and Chikmagalur Districts.

The Coconut Development Board has provided $150 000 to state governments for pick-up construction under the million wells scheme. The amount spent on each pick-up will vary depending on the command area served by the pick-ups. Normally petitions are submitted by the villagers through their local government bodies (such as gram or mandal panchayats) to the zilla parishad or public works department. A survey of the site proposed by the villagers is conducted by the public works engineer, and an estimate of the construction cost is sent for approval to the district level engineer. After the technical evaluation, a financial sanction is obtained, and a contract is awarded to the registered contractors. Construction work is undertaken usually during the summer season.

Technical Description

The construction site is selected in an area with exposed bedrock to ensure a strong foundation. The stream is also narrow at such sites, and the sites typically form convenient sites for road crossings. Upstream of these constrictions, there is generally an area available for spreading the water more widely (the floodplain of the stream), and the back water created by the pick-ups can extend up to nearly one-half of a kilometre in length.

During the construction phase, a cofferdam created by about 200 polyethylene sandbags are used to make a temporary bund. Within this bund, boulders are placed upon the bedrock in a slanting manner to form a permanent bund. Each stone weighs between 100 kg and 1 000 kg, and are generally transported to the site in a power tiller trailer over a distance of between 0.5 km and 5 km. Wooden planks are used to load and position heavy stones. Behind this rock wall, a supporting vertical wall with a width of 10 cm is built, and both walls are raised simultaneously. Between the walls, an impervious core is created by a layer of "crude jelly" (bitumen) encased within a layer of clay. The clay is wetted to produce a slurry which is compacted by repeated passes of the power tiller to ensure a good seal, and further clay is added until the entire structure is encased in earth. Construction usually takes place over a period of several years.

During the first year, the total height of the bund is only about 5 cm above the stream bed, although the side embankments or wing walls are constructed on either side to a height of 10 cm to prevent the failure of the banks during periods of high flow, when the structure is overtopped. On either side of the bund, stone pillars are erected to enable people to locate the bund during peak flow periods, and to assist them in crossing the stream when the pick-up overflows. During the second year, after observing the water flow of the previous year to determine the effects of any seepage, overflows (possible flanking of the wing walls) and impoundment (to determine the ability of the structure to withstand the water load), further construction occurs and the height is increased by another 4 cm. The length of the pick-up increases as the height increases. During the second year also, work is completed prior to the monsoon. During the third year, after observing the water flow, the height is further increased by another 4.5 cm until it almost reaches the ground level. On completion, the surface of the pick-up is covered with stone slabs to prevent erosion of the clay surface. At this juncture, the entire structure is encased within a mud embankment, built to a height of 0.75 m (2-1/2 feet) above the stream bed, and turfed with Maane hullu grass to prevent erosion and stabilize the stream banks.

The Tumkur pick-up, constructed in the above manner, is almost impervious and has withstood even the heavy stream flows in the last five years (since 1991).

Extent of Use

The Tumkur pick-up is a typical coconut pick-up, and is one of five such structures situated on this water course. The Tumkur pick-up was selected for this study as information was available for the entire period of the construction project and for the 7 year operational period. It is the third pick-up in the catchment. The watershed of the Huvinahalla Stream which feeds the pick-up originates in the Handanahalli Hills. Stream flow is seasonal, with the stream flow dependent upon the annual rainfall. Nearly 90% of the stream reach passes through coconut plantations or gardens.

The Tumkur pick-up was designed and built by an individual farmer, and constructed using locally available materials. The design was approved by, and construction inspected by, the public works department prior to the implementation of the project. The formal inspection process and granting of operating permission by the public works department is intended to avoid litigation by downstream farmers. The project was completed over a span of three summers, with the height of the pick-up being raised each year until the crest of the weir was almost at ground level. The crest of the weir is stabilized and is used as a cross-over road to reach the other stream bank during high flow periods.

Details of the number of pick-ups, and their command areas and beneficiaries in the Tumkur District for the period 1991-92 to 1994-95, are given in Table 22. Table 23 shows typical construction dimensions of these structures.

Operation and Maintenance

The pick-ups are constructed by individual farmers, who are responsible for both the operation and maintenance of the structures. The primary maintenance requirement is that the structure remain impervious to minimize the possibility of dam failure.

Level of Involvement

The pick-ups are managed by the individual farmers who build, operate and maintain the structure. Government may be involved in the funding and/or initial sanctioning of the project site, and in the inspection of the dam. Mainly, governmental actions will be carried out by the local self-governing bodies involved.

TABLE 22. Pick-ups in the Tumkur District Constructed Under the Million Wells Scheme.

^aNA = Data Not Available

TABLE 23. Typical Dimensions of a Coconut Pick-up.

The rights of the farmer who has constructed the pick up are as follows: the farmer may make use of the silt accumulated behind the bund; the farmer may construct a storage tank and provide such tanks with a sump from which to pump water that has been conveyed to the tank from the pick-up (however, neither the farmer nor any other individual can directly pump water from the pickup); and, the farmer can raise bamboo, teak and other suitable species of tree on their katha bund (wingwalls) and along their periphery.

Costs

The costs incurred in the implementation of this technology are summarized in Tables 24 and 25.

TABLE 24. Capital Cost of Project Implementation.

Effectiveness of the Technology

This technology augments available water resources by storing surface water and recharging groundwater. As shown in the data provided in Table 26, there was an observed recharge in six open wells as a result of infiltration from the coconut pick-ups from the second year onward.

This traditional technology is ideally suited for the local conditions prevailing in this region of India. In terms of costs, the pick-up is valued at about $7 000, based upon the nominal rates used by the government ($353/ha). However, by using locally available materials and using existing farm labour, the farmer actually spent $1 825 in constructing the Tumkur pickup. It is therefore important to create awareness of this technology amongst the farmers, and encourage local initiatives in its construction.

TABLE 25. Details of Expenditures Incurred.

*Imputed costs

Advantages

The principle benefits which may be derived from using this technology include:

· The availability of impounded water, the depth and extent of which depends upon the terrain, width and depth of the stream, and the duration of which depends upon the soil type, usage and frequency of rainfall/refilling.

· Enhanced groundwater recharge due to both vertical percolation and horizontal interflow, revitalizing percolation tanks, open tanks and tube wells; the recharging of open wells is almost immediate within a radius of up to one-half of a kilometre depending on soil structure and gradients.

The ponds created by the pick-ups serve as drinking water sources for livestock from 8 to 10 villages in the communities surrounding the pick-up. These ponds also serve as a common place for washing clothes and conducting religious ceremonies (Ganga Pooja); for seasoning wood and wooden poles by submerging them in water, which is a common practice; for retting coconut husks and agave leaves; and for other, similar activities. The waterbodies attract birds and serves as habitat for aquatic creatures, and can provide water for pisciculture. Agroforestry practices can be implemented along the periphery of the waterbody, which creates a microclimate that is more congenial for the growth of plants, including coconut and arecanut plants.

The pick-ups reduce the impacts of soil erosion and downstream siltation, while retaining silt that can be collected in the pick-ups and carted off to the coconut plantations during summer months to improve soil structure and fertility, and, in turn, increase their productivity. The pick-up structures can also serve as a vital link between villages, especially during the rainy season when travel may be restricted by flooding rivers.

In certain areas, seepage into percolation wells as a result of groundwater recharge from the pick-ups is used to irrigate coconut and arecanut gardens, other field crops like ragi and maize, and even paddy crops.

TABLE 26. Benefits Derived from the Use of Pick-ups.

^a Direct Benefits include the plantations benefited by flooding as well as groundwater irrigation;
Indirect Benefits comprise the plantations benefited by groundwater recharge.
^b An additional benefit is the reduction of siltation downstream.

Disadvantages

Possible disadvantages include increased nuisance due to mosquitoes breeding in stagnant water that may collect upstream of the pick-up structures.

Further Development of the Technology

Based on the aforementioned observations, methods of involving the local people in planning and executing such projects is very important to achieving long lasting benefits from such ventures.

Information Sources

Gracy C.P., B.L. Chinanda, C.K. Jalajakshi, and K.H. Vedini 1995. Traditional Methods of Soil and Water Conservation - A Case of Coconut Pickups. In: Proceedings of the National Workshop on Traditional Water Management for Tanks and Ponds. Centre of Water Resources and Ocean Management, Anna University, Madras.