IWMP-11 - Commissionerate of Rural Development Gujarat State ...

DWDU, Rajkot
of a watershed a contour bund/trench is a simple and inexpensive solution to slowing down surface runoff and reducing soil
erosion.
Objectives
1) Slowing down the velocity of runoff
2) Checking soil erosion
3) Improving local soil moisture profile
Contour bunds/trenches are constructed in the ridge area of a watershed. Rainwater, which falls in this area flow unchecked
carrying with it eroded soil into the flatter portion of the watershed - the "valley". This silt gets deposited into reservoirs and
ponds, reducing their life. Thus, any water harvesting work undertaken in the valley will become meaningless unless appropriate
measures such as contour trenching are undertaken to control runoff and soil erosion in the ridge. Contour trenches collect the
rainwater that falls in the ridge area. This way the soil moisture profile in the area adjacent to the trench is improved.
b. Boulder Checks /Loose Boulder checks
Boulder checks or gully plugs are loose rock dams made on small drainage lines or seasonal streams which have a catchment area
of less than 50 ha. It is adopted where the water velocity is high and where basically stone available with in radius of 100-150 m from
the site. The main aim of constructing loose boulder checks is to reduce the velocity of water flowing through the drainage line. By reducing
the velocity of runoff, boulder checks help in:
1. Reducing soil erosion;
2. Trapping silt which slows the rate of siltation in water harvesting structures in the lower reaches of the watershed.
3. Creating a hydraulic head locally which enhances infiltration of surface runoff into the groundwater system; and
4. Increasing the duration of flow in the drainage line. Therefore, the capacity of the water harvesting structures created downstream on the
drainage line is utilized more fully as they get many more refills.
Detailed Project Report: IWMP-11 79