APPLICATION OF THE SWAT MODEL FOR INTERLINKING OF RIVERS - A CASE STUDY OF KEN SUB-BASIN OF YAMUNA BASIN

Abstract

The first Prime Minister of independent India, Pandit Jawaharlal Nehru famously declared "Dams are temples of modern India". The role of major Water Resources Projects, in our nation's socio economic development since independence could not be ignored. Now at a time when, the effect of uneven spatial and temporal uneven distribution of available water resources over the country is becoming more pronounced and water related disputes at all levels becoming the order of the day, the need of the hour is to realistically and scientifically assess the availability of water resources and thrive for achieving their optimum utilisation. One of the viable concepts to mitigate spatial uneven distribution of water resources could be Inter Basin Water Transfer as proposed under Inter Linking of Rivers Schemes. To justify and showcase the technical viability of such schemes more convincingly, wider use of physically based distributed hydrological models in hydrological analysis would help in a long way in the hands of Water Resource Planners In the present study, the continuous time step, semi distributed hydrological model, the SWAT has been applied for the Ken basin, The Ken basin is an integral part of the Ken — Betwa Link Project proposed under Inter Linking of Rivers schemes and is under active consideration for implementation. The present study area comprising the Ken basin lies between Latitudes 23°8'3"N & 25°53'15" N and Longitudes 78°30'57"E & 80°37'53"E covering an area of about 28570 km', in the states of Madhya Pradesh and Uttar Pradesh. The Ken river is a tributary of the Yamuna river which in turn is a major tributary of the mighty and holy Ganga river. The observed discharge data of the Ken river at Barida site collected from the Central Water Commission has been used for calibration and validation of the model. The daily rain fall data of 15 rain gauge stations located in and around the study area is collected from India Metrological Department and required weather data has been download from the NASA web site. The soil maps and soil data of National Bureau of Soil Survey and Land Use Planning have been used for the soil classification of the study area. The DEM based watershed delineation of the study area is done with ASTER data sets downloaded from www.gdem.aster.esrdac.or.jp site. The supervised classification for land use I land cover determination is done with the TM data sets downloaded from http:// glcfapp.glcf.umd.edu site. The ArcSWAT 2009 interface of the SWAT model set up is done for the study area by overlaying maps of Soil class, Land use class and slope class. Based on unique land management practices (Land use / land cover), slope and soil classes and considering the location of outlets for calibration, the study area has been divided into ten sub basins consisting 107 HRUs. The missing rainfall and weather data is generated by the inbuilt weather generator of the SWAT model. The Penman-Montieth method is selected for ' estimation of potential evapotranspiration and the SCS runoff curve number method is used for surface runoff estimate. The period from 1981 to 1985 (4 years) is treated as model warm up (equilibration) period, from 1985 to .1996 as calibration period and, the period from 1997 to 2009 is considered for validation. Manual calibration is employed in monthly time steps using the observed discharge data of Ken river at Banda site. Since the SWAT model considers rainfall data of one rain gauge station for all the HRUs in a sub basin, to account for spatial variability of occurrence of rainfall over large sub basin areas, weighted average daily rainfall based on Thiessein's polygon methods is computed for each sub basin. The SWAT simulation is carried out using both the sets of rainfall data viz., individual station rainfall (SRF) and weighted average rainfall (WRF) and results compared. Base flow separation of the observed daily discharge data is also attempted, but the separated base flow fraction could not be reasonably validated for lack of independent observations. Based on recommended evaluation ratings, the performance of the SWAT model for the study area is very good during calibration period and the same is satisfactory during validation period. Irrigation and conservation practices were simulated to predict the affect on hydrological response from the watershed. The simulated surface runoff at Daudhan dam site is compared with the surplus yield series computed at the darn site in the Detailed Project Report of Ken — Betwa link project and it is found that non monsoon runoff is significantly higher in case of the SWAT simulation. These results could be used to review the required reservoir capacity at the Daudhan dam site to meet the envisaged demands.