Development and calibration of a soil water balance model for paddy field in humid climatic condition.

Abstract

Study was conducted in Munijhara watershed located in Nayagarh block of Odisha (India), which is mainly dominated by hard rock aquifer. Groundwater withdrawal was more than the annual recharge to the aquifer, which resulted in decline of ground water table depth over the years. Natural groundwater recharge was estimated to be around 13-40 cm/year. Attempt has been taken up towards increasing the recharge rate to the aquifer by various means. As paddy field contributes maximum amount of percolation to groundwater, a soil water balance approach was developed for estimating percolation losses in the paddy field during Kharif 2007 and 2008 for both unsaturated and saturated conditions. For modeling purpose, the effective root zone of paddy (45 cm) was considered as a single layer, upward capillary rise of groundwater was neglected. All observed water balance components were compared with the model data. A good correlation coefficient was obtained for simulated evapotranspiration and seepage. As it is difficult to empirically measure the exact percolation rate due to heterogeneous water movement in the soil profile, simulated percolation rate were found to follow a similar trend with that of the observed values. The objective was to understand and rate of percolation in different soil conditions within the watershed, and results of soil water balance model could be used as one of input to the groundwater model. Based on the soil-water balance approach, it was calculated that about 16-23% of total rainfall received during cropping period (paddy) was percolated down and contributed to the groundwater. For regional scale modeling approach, it is needed to combine both soil water balance and groundwater model for quantification of any hydrological components. Hence findings showed that soil water balance method can be used to estimate recharge in a particular basin and the result can very well be an input while designing an integrated groundwater model at a macro level or at a regional scale.