The following is a of thumb classification for selecting the type of structure for the particular watershed area. Watershed Area Purpose of Interventions Classification Structure This is the area that the water source originates from. Usually on steeper slopes, erosion is high in this area and the water runs off quickly. If the water flows too quickly, streams downstream will get silted. To avoid this, certain structures may be built which slow down the flow of water. Erosion can also be checked by planting grasses, shrubs, trees and permanent forest cover. On slopes greater than 25%, a) Contour Trenching. Protection and plantation of grasses, shrubs and trees native to the area b) Where boulders are available, contour bunding with boulders. It is might be good idea to go for permanent vegetation through planting local species and perennial grasses. On slopes between 10-25% Contour staggered Trenching On slopes less than 10% Earthen Contour Bunding. 30X40 model is better than contour bunding because it is very difficult to follow a contour while constructing earthen bund, and mistake in following bund can result is breaking of bund. Drainage This is the area between the ridge and farm, that is, where the water flows down to the farm. There will a gentler slope. This area too will have erosion and siltation. Structures built here will also be intended to check erosion and avoid siltation of water bodies downstream. To do this, drainage channels are deepened and local bed slopes> 20% Brushwood checks Gabion structures where velocity and volume of peak run-off is too high for loose boulder structures local bed slopes < 5% a) Earthen dams, which serve as percolation reservoirs in the upper catchment. b) Sand-filled bag structures in to check the velocity of stream flowwhere sand is locally available c) Gabion structures where velocity and volume of peak is too highfor loose boulder structures stream embankments severely eroded a) naala training, including deepening channels and raising embankments,along sections of
embankments are raised along sections of the streams that overflow and flood. streams, where during peak floods, the stream flows over its embankments and damages the fields alongside b) embankment stabilisation through gabions or sand-filled bag structuresin stretches where the banks are particularly vulnerable and needreinforcement bed slopes between 5-20% loose boulder checks groundwater harvesting are located alongside Underground dykes in the discharge zone where the impermeable strata areoverlain by thin layer of permeable deposits Farm Since this is where water drains out, it is the most fertile and suited for agriculture related works. Tap surface water and recycle to irrigate second crop. Save crops from dry spells by providing life saving irrigation Improve soil moisture. Permeable/dry soil Water harvesting Tanks System of bunds and diversion channels for a stretch of fields from local ridge to drain. While in permeable soils the bunds help increase soil-moisture profile WHTs to catch the runoff from the farm land. It increases infiltration and, checks erosion, increases soil moisture regime, increases ground water level. Waterlogged Seepage Tanks Low Land wells Seepage drains which help vertical drainage of excess soil moisture into permeable strata underlying the top soil, simultaneously increasing. Seepage tanks to catch the seepage water and lateral flows, very useful to cultivate second crop after rainy season. Groundwater recharge, system of and diversion channels Low land can be dug in low lands with good seepage and water can be used in the same field in summer season and lifted to distant uplands during rabi season when low lands are water logged.