WRD works done in a Wadi project are different from works undertaken in conventional watershed development programmes.
Wadi project areas comprise mostly forest villages where over 60-70% of the total land is under forest cover and the rest is owned by local families. Further, most of the agriculture lands are sloping. Hence, many structures of conventional watershed development programmes are not feasible, and various innovative methods have to be used to tap water resources:
Good sources of water in many project areas are rivulets and gullies, which carry water for 4-6 months during and after the rainy season. Construction of checkbunds with soil or cement across these rivulets is not generally advisable as the rivulets are prone to heavy flooding, and the catchment suffers heavy siltation. Instead, temporary checkbunds are constructed by placing sand bags across rivulets towards the end of the rainy season. The water is used to cultivate rabi crops and irrigate fruit orchards.
Temporary checkbunds can be built for around Rs 5000 each and the work can be completed in 2-3 days by local youth. In many Wadi villages, farmers have built bunds without project support.
Water stored behind checkbunds can be channelled by gravity to plots at lower elevations. In most cases, water is pumped and used by a group of farmers.
The structure is usually washed away in the subsequent monsoon and has to be rebuilt. See practical tips for building seasonal bunds.
Earthen and masonry percolation tanks
At some sites, earthen dams or masonry structures can be constructed to plug gullies and use the catchment area as a percolation tank. A critical prerequisite is that beneficiary farmers should have ownership and control over the catchment area.
Checkdam or overflow weir
This is a low weir without a canal, built across small streams or nallas having a continuous flow of water particularly during the rabi season. The water is used for lift irrigation or to recharge aquifers in the surrounding area, which feed open wells and tube wells. Cost of construction is reduced by using ferrocement technology.
Lift irrigation is used to distribute water collected in percolation tanks, behind checkdams, as well as water flowing through rivers. Water is lifted and transported to farm ponds and tanks constructed by farmers.
A lift irrigation unit comprises three elements:
- A water lifting structure, comprising intake well or headwall, intake pipe, jack well and pump house, pumping machinery with suction and delivery pipes and power unit
- A conveyance system in the form of a rising main pipe, gravity main pipe or open channel
- A distribution system comprising a delivery chamber and an underground pipeline or open channels with suitable outlets.
Considering the disadvantages and cost of permanent installations, mobile lift irrigation schemes have been used in Wadi projects. Diesel engine pumps are mounted on hand- operated carts or bullock carts. The carts are moved to different locations, to meet water demand of different farmers.
In the areas where forest cover is high, natural springs are common. Special efforts are made to collect water from these springs, to use for drinking purpose, irrigate vegetable plots and nursery plants, and to protect the catchment area from deforestation.
The elements of a standard spring development and protection scheme include:
- an intake structure
- collection/storage tank
- tap stand
- retaining wall
- arrangement for overflow
The intake structure with a filtering media is located at the source of the spring and conveys spring water into the storage tank.
The intake channel can be of a PVC/GI pipe or a trapezoidal channel of masonry filled with gravel filter media. Capacity of the storage tank is calculated on the basis of the number of dependant households. Typically, if daily water demand per household is 100 litres, 10 dependent families will require a tank of 1000 litres capacity. If the tank has to fill overnight, minimum discharge of the spring has to be 1.4 litres per minute.
The tank is constructed using UCR, brick masonry or ferrocement. Overflow can be collected in a trough constructed at a distance of about 15-20m from the tank. This water can be used by cattle for drinking.
In Wadi plots where percolation of rainwater is low, trapezoidal farm ponds of various sizes are dug to store rainwater. The water is used to irrigate fruit trees, food crops and vegetables. Pond size can vary from 5m x 5m to 10m x 10m or more. See practical tips for constructing farm ponds.
Jalkunds are low-cost water tanks built in orchards. Small rectangular ponds, with capacity to hold 2000-5000 litres of rainwater, are dug and the sides are covered with a plastic sheet to prevent seepage. A jalkund with 4000 litres capacity can provide 10 litres of water every week to 10 trees of mango or cashew from November to June.
When good groundwater resources are available, and there is no other water source available, open wells are constructed for the benefit of 4-6 or more Wadi plot-owning families, with their contribution in the form of labour. Pumps to lift water from the well are bought by the beneficiaries with or without credit support from the project. The beneficiaries themselves formulate rules for lifting water and maintaining the well and pump(s).
Land required for the well is donated by one of the beneficiaries, who formally agrees that the well will always be a resource shared by identified families.