IWMP-3 - Commissionerate of Rural Development Gujarat State ...

DWDU, Rajkot
1. Contour Bunds/Trench
Contour bund/trenches are a simple, low-cost method of checking the velocity of runoff in the ridge area of any watershed. A contour
trench is a trench dug along a contour line. A contour line is an imaginary line that joins together points of the same elevation. Digging a
trench along a line that is at the same level increases the chances of containing runoff for a longer period of time within the trench. If
bunds/trenches were not to follow a contour, such digging could actually increase the possibility of soil erosion because there would be a
rise in the velocity of runoff following upon an increase in the slope of the land. In the ridge area 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.
2. 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;
Detailed Project Report: IWMP-III 63