Estimation of Water Balance Components of Patapur Micro Watershed in the Tungabhadra River Basin Using QSWAT Model in QGIS Environment

Aims: Estimation of water balance components of a micro watershed by employing efficient calibrated and validated SWAT model helps to understand each components of water balance and are important to plan agricultural water management, climate change impact assessment, flow forecasting, water quality assessment etc. This water balance study minimizes possibility of drought and mismanagement, and hence will lead to a proper utilization of accessible water resource.

Place and Duration of Study: In the present study, QSWAT hydrological model was calibrated and validated using measured runoff data from the outlet of the micro watershed and then put to use for long term simulations in Patapur micro watershed, Raichur District, Karnataka using weather, land use and land cover, soil and digital elevation model for the period of 37 years (1980-2016).

Methodology: The QSWAT model was set up using the input data of Patapur micro watershed and was accurately calibrated and validated using the measured runoff data. The calibrated was used for long term simulation from 1980-2016 and then water balance components of the micro watershed was estimated.

Results: The results revealed that the QSWAT model performed better in simulating the runoff and other water balance components. The daily calibration statistics results for behavioral parameters in SWAT-CUP for stream flow discharge during the period 2012-2014 are R2, NS, PBIAS and RSR values between measured and simulated by model was found to be 0.88, 0.87, -21.30 and 0.36, respectively indicating the model performance for daily calibration was very good in terms of both R2 and NS value as their value being >0.75 as per the performance ratings of hydrological model.

The water yield that is draining out of the watershed includes surface runoff, lateral flow and groundwater contribution to stream flow minus the transmission losses (water lost as deep percolation and evapo-transpiration) which amounts to 168.40 mm. The annual water balance components for the watershed indicated that out of 527.70 mm of annual precipitation, 322.50 mm and 114.91 mm was lost by evapo-transpiration and surface runoff, respectively. The water balance also revealed that 82.86 mm was contributed to groundwater by percolating into shallow aquifer which was followed by 43.40 mm of base flow but the ground water recharge and storage is very meager that accounts to only 4.14 mm that is the matter of concern over the micro watershed. The simulation model indicates that 58.77 to 64.54% by rainfall was lost by evapotranspiration and very less amount lost through the lateral flow. Groundwater flow and percolation were contributing 3.68 to 10.13% and 9.95 to 19.82 % respectively, from total rainfall. During the highest rainfall year, about 33.22, 10.13% and 1.10% of the rainfall was transformed into surface runoff, groundwater flow and lateral flow respectively. During lowest rainfall year, about 8.31%, 3.68% and 1.35% of the rainfall was transformed into surface runoff, groundwater flow and lateral flow respectively.