Coupled 1D hydrodynamic-water quality model of Kobadak-Sibsa River system for salinity

Abstract

Salinity intrusion creates severe problems in agriculture and drinking water sources in the floodplain of tidal rivers due to low upstream flow and climate changes. This study focuses on 1-D advection-dispersion modeling of the Kobadak-Sibsa river by HEC-RAS. This work has been carried out in simulation of temporal distribution of salinity concentration in different locations which help to identify which location exceeds the chloride limit of drinking water of 1000 ppm and chloride limit in agricultural water limit of 1500 ppm. The hydrodynamic model was coupled with 1D salinity modeling. The calibration was done for the month June 2016. Then the validation was done using the data of July 2015. It has been found a good agreement between simulated and observed water level for Manning's roughness coefficient as 0.021. Once the hydrodynamic model was calibrated and validated, the 1D advection-dispersion model was performed and calibrated and validated for the year 2016 and 2015 for different dispersion coefficients (D) for different reaches as a tuning parameter. It has found that the higher the dispersion co-efficient the higher the salinity concentrations that the dispersion co-efficient varied from 25 m2/s to 9000 m2/s which showed good agreement between simulated and observed salinity data. From December salinity gradually increases and reaches its peak in April or May. Maximum salinity concentration has been determined in different locations by simulating this model. This hydrodynamic and water quality coupled modeling can be helpful for lesson learning to prevent salinity intrusion in the Kobadak river.