Page - 598 - in Book of Full Papers - Symposium Hydro Engineering

Table 1 Land use categories in the study area SWAT code Descriptive Term % of Catchment Area URLD Low density urban 30.14 AGRR Tea 26.84 FRSE Forest 19.91 SHRB Scrub 6.76 RICE Paddy 6.19 3.2 MODEL SIMULATION Model development was done using the QGIS QSWAT interface and associated SWAT Editor tool. The model generated the river network based on the DEM where the threshold value selected was 25 km2. According to this river network the model delineated 52 sub basins within the study area. The DEM was categorized into four slope bands as 0-10%, 10-20% and 20- 30% and above 30%. During the simulation model created similar sub units with similar hydrological response known as Hydrological Response Units (HRUs). HRUs are areas within the sub basins where slope, land use and soil types are similar. An area threshold of 10% was applied to land use types in order to avoid minor land use types in sub basins to simplify HRU creation. The model was run for the period 1960-2016 in a monthly time step. 4. RESULTS AND DISCUSSION The model calculated daily sediment yield in the basin area from the beginning of 1960 to the end of 2016. As the rainfall is varying throughout the year the annual series of sediment yields is more appropriate for a trend analysis. The annual totals were plotted for analysis excluding the first and last year of the modeling period to avoid modeling errors due to mass balance (Fig. 2). It can be observed that highest sediment yield in the basin has been 1,022,717.31 Ton as reported in 2013. The average yield of area for the total period (1961-2015) has been 48.55 Ton/km2/year. However, all the sediments formed due to erosion will not reach the reservoirs as part of it deposits within the catchment itself. On the other hand all the reservoirs have been commissioned around 1985 and soil erosion taken place prior to that time has not contributed to reservoir sedimentation. 598