Watershed Analysis of Two Forest Catchments from Western Ghats, South India and its Significance for Mitigation of Reservoir Siltation

Estimation of water balance and sediment yield pertaining to two forest watersheds of southern India was carried out as part of the forest conservation program in Kerala State. The tropical watersheds namely Upper Peppara (-80km²) and Upper Neyyar (-140km²) of southern Kerala region host two important wildlife sanctuaries maintained in the Western Ghats of Indian subcontinent, which have high biodiversity values. The watershed evaluation conducted during the period 1995-2000 reveals that Peppara reservoir catchment yields an average of 1600 tons of suspended sediment and 126Mm³ of run off water every year. On the other hand, Neyyar reservoir at Full Reservoir Level (FRL) carries a suspended sediment load of 1400 tons during the peak monsoon month of June and it receives 207Mm³ of run off from its catchment annually. Unit plot measurements for soil loss indicate that grassland yields substantially high sand-Silt material, of the order of one ton per hectare annually. A management plan map for the Upper Neyyar watershed has been prepared taking into consideration of landscape features. One micro watershed, Panampara (6.73km²) falling within Peppara sanctuary was closely monitored to check its physical health. A number of locally feasible conservation strategies have been proposed to improve the water holding capacity as well as to minimise soil erosion in this subwatershed area. Periodic and manual silt removal from reservoirs during summer periods is recommended to maintain the storage capacity rather than constructing an upper dam or increasing the height of existing dam, as actively being considered.