A revised soil erosion budget for India: role of reservoir sedimentation and land-use protection measures

Among the different controls of erosion budget at basin level, the relative impact of dams and land management is yet to be investigated. In this paper, the impact of dams on sediment yield has been assessed by using a conceptual modelling framework which considers the gross erosion and the cascade of dams constructed on a river network. The sediment budget has been estimated based on the gross erosion, deposition of sediment in reservoirs, and sediment yields of 23 mainland river basins of India. The gross erosion of the country is estimated as 5.11 +/- 0.4 Gt yr(-1) or 1559 t km(-2) yr(-1), out of which 34.1 +/- 12% of the total eroded soil is deposited in the reservoirs, 22.9 +/- 29% is discharged outside the country (mainly to oceans), and the remaining 43.0 +/- 41% is displaced within the river basins. The river basins of northern India contribute about 81% of the total sediment yield from landmass while the share of southern river basins is 19%. The components of revised sediment budget for India are prominently influenced by the sediment trapped in reservoirs and the treatment of catchment areas by soil and water conservation measures. Analysis of sediment deposition in 4937 reservoirs indicated the average annual percentage capacity loss as 1.04% though it varies from 0.8% to >2% per year in smaller dams (1-50 Mm(3) capacity) and from <0.5% to 0.8% per year in larger dams (51 to >1000 Mm(3) capacity). Siltation of smaller dams poses a serious threat to their ecosystem services as they cater to a wider population for domestic, agricultural, and industrial purposes. Amongst the environment controls, land use significantly impacts the gross erosion rate and specific sediment yield as compared to climatic and topographic parameters. However, to analyse their integrated effect on the complex processes of sediment fluxes in a basin, further research efforts are needed. Copyright (c) 2016 John Wiley & Sons, Ltd.