MEASURES FOR WATERSHED IMPROVEMENT
Measures for Management of Arable Land:
Arable Land of watershed is very much prone to erosion by raindrop splash, run-off and man-made activities.
The mechanical measures or management works needed in arable land are :
i) Bunding
~ Contour Bunds
~ Graded Bunds, Side Bunds and Lateral Bunds
ii) Diversion Drain and Grassed Waterways
iii)Bench Terracing
iv) Conservation Bench Terrace
v) Conservation Ditches (Contour Ditches)
vi) Outlet Structures
vii) Land Levelling
viii) Some Hydraulic Measures
ix) Retaining Wall in Hill Cutting
x) Vegetative Measures
Contours bunds constructed along a contour.
Farmers with small and scattered lands adopt compartmental bunds.
Graded bunds, side bunds and lateral bunds are constructed in areas where run-off water is not readily absorbed. Sometimes it is essential to construct supplemental bunds between two contour bunds and peripheral bunds along field boundaries. This intercepted water is diverted across the slope to a grassed waterway, which is an important soil conservation practice. It works as an outlet to dispose of the surplus water safely into the natural drainages and thereby protect the land against rills and gullies.
Besides being outlets of diversion drain, grassed waterway acts as emergency spillway and farm pond.
Bench terracing is another mechanical method by which reduction of slope in hilly areas is done by constructing bund and then cutting and filling of land surface as per prevailing ground conditions.
In conservation bench terrace, run-off water is impounded at a lower part levelled by cutting and filling Rice is grown in this part and wheat and maire that require less water are cultivated in the upper part. Conservation ditch or contour ditch is found to be more suitable in black soil.
Some outlet structures to dispose of surplus or water accumulated upstream of contour bunds are clear over fall stone weir, channel weit, cut outlet pipe outlet and ramp cum-waste weir.
Natural topography of watershed excess is not always levelled. Therefore, land levelling is performed on such ground level of watershed for even distribution of water for better production.
Some hydraulic structures are required to be constructed in arable land, for example, canal lining in irrigation canal to control seepage, hydraulic structures to create hydraulic jump to dissipate the water energy to control soil erosion, canal fall structure to reduce velocity and soil erosion, retaining wall on slope of hill cutting to obstruct the sediments with runoff etc.
Besides mechanical or engineering measures, biological or vegetative measures are also adopted in the next step. The engineering and vegetative measures are not alternative but complementary.
Both measures are necessary for the complete watershed management.
Some important biological measures are contour farming or cultivation, strip cropping, vegetative barriers or live bunds, crop residue, mixed cropping, hedge row barrier, alley cropping natural type bench terracing, etc. Some other methods to control erosion and sediment in run-off are tillage operation, adoption of organic measures and green manures, controlling deforestation and precautions on natural hill cutting.
Measures for Management of Non – Arable Land :
Following are the measures for watershed management
i) Contour Trenching
ii) Orchard Terraces
iii) Diversion Drain
iv) Stone Walls
v) Vegetative Control Measures
vi) Half-Moon Terraces
vii) Geojute
viii) Retaining Walls
ix) Wattling
x) Crib Structures
xi) Gunny Bag Structures
xii) Soil and Water Conservation Measures for Landslide Control
xiii) Micro Watershed Treatment
xiv) Vegetative Barrier to Prevent Wind Action on Soil Erosion
The various methods are parallel and staggered contour trenches with a bund in downstream side along a contour across the slope, a series of orchard terraces in steep hill slope, diversion drain which collects run-off to divert to natural drainage, a series of stone walls in the form of bund constructed across the hill slope for developing non-arable land to obstruct the sediments, debris flowing down the hill, vegetative cover on non-agricultural land, individual basins or terraces in the form of hall-moon or semi-circle in hilly slope, application of geojute or jeotextile, essentially a matting made by 2-5 mm thick jute yarn having 10 mm aperture, for stabilization of highly degraded non-arable land, some of the protected terraces used in the management of hill slope of watershed, retaining walls at areas vulnerable to landslide, more specifically during monsoon period, wattling for breaking the slope of the ground into shorter portions by providing wattles along the contour, the crib structure made of eucalyptus poles to stabilize land slope, cheap, easy and quick gunny bags for slope stabilisation, micro watershed treatment for planting different fruits or crops on a sloppy region, different kinds of vegetative barriers used to reduce the bare soil erosion by the action of wind, etc.