PATTERNS OF SILTING IN THE RESERVOIRS OF SMALL- AND MEDIUM-SIZED EARTHEN CHECK DAMS IN THE SHIWALIK FOOT HILLS OF THE HIMALAYAS

Silting of reservoirs is a ubiquitous process in all types of dams. Despite substantial work on the rates of silting, the spatial pattern of silting in reservoirs is not clearly understood. While it is anticipated that the variability of silting increases with decreasing reservoir size, not much is known about siltation in sub-tropical humid regions. This paper presents the initial results of geomorphic analysis of six earthen check dams in the Shiwalik foot hills of the Himalayas (India) in areas with relatively high proportions of disempowered populations. These check dams include three small-sized dams (Dhamala-II, Rel Majra, and Sukhomajri-II) and three medium-sized dams (Bunga-I, Parachh-II, and Siswan). Field data were collected from each reservoir. The methods used included spatial interpolations of bed depth and silt thickness in each reservoir, Structure from Motion to extract multiple channel cross-sections from photographic scans along tributary mouths, determination of the concentration of organic material in silt samples, texture analysis of bed and bank materials, and visual observations of stratigraphy of hill slopes around the check dams. The results reveal that the degree of silting varies between small- and medium-sized reservoirs. Most silt is mineral in nature and tends to concentrate either in the middle portion of the reservoir or near the dam but not always along the dam or in the thalweg. Downstream areas of these check dams are heavily used for various human activities and the channel network has almost been eliminated.