Page - 597 - in Book of Full Papers - Symposium Hydro Engineering

Accordingly this methodology was applied to check whether sediment yield output time series had got any trend. 3. METHODOLOGY 3.1 MODEL DESCRIPTION Soil Water Assessment Tool (SWAT) was used as the modelling software for this study. SWAT is a continuous hydrological simulation tool jointly developed by USDA Agricultural Research Service (USDA-ARS) and Texas A&M AgriLife Research. It is GIS-based and simulations can be done at daily time intervals. In addition to hydrological modelling SWAT is capable of calculating the sediment yield of a river basin as well. Accordingly, a SWAT model was developed for the study at a daily time-step for the period 1960 to 2016. Although all the reservoirs in MRUB have been commissioned around 1985, a longer period was taken into account to check any impact form climate change on sediment yield of the basin. The primary inputs to the model were the basin Digital Elevation Model (DEM), digital land use map, digital soil map, daily rainfall and temperature data of meteorological stations within the study area. A Subtle Radar Terrain Model (SRTM) downloaded from United States Geological Survey was used as the digital elevation model. The resolution of the model was adjusted to 60m. The elevation of the area varied from 423 m to 2070 m MSL. The land use data were obtained from Land Use Planning Policy Department and digital soil data from Agriculture Department. Daily rainfall data and temperature data were obtained from Meteorological Department. As no previous land use data maps were available the latest map was used for the total modelling period. In fact, there had not been any significant land use changes in the area and it was a valid reason for using the same map for the whole modelling period. The description of major land use categories are given with the percentages available in the study area (Table 1). It is interesting to note that nearly 20% of the area consists of forests which would least contribute to overall sediment yield. Daily rainfall data of 11 rain gauge stations located within the area were used. For daily minimum and maximum temperature data four climatic stations, within and around the basin were used. Unavailable climatic data; solar radiation, wind speed and relative humidity were generated by the model itself using a weather generator provided with SWAT [4]. 597