The Application Of GSFLOW—a Coupled Surface Water And Groundwater Model For Shaying River Basin

Interaction of groundwater and surface water is an important component in hydrologic cycle.It is necessary to consider the interaction in the water transformation and resource management in a basin.In this thesis a coupled GSFLOW model developed by USGS was built to study the surface water and groundwater interaction and transformation in the Shaying River basin.The impacts of urbanization and dam construction on river runoff in the basin basin were studied with the calibrated and verified GSFLOW model.The Shaying River basin is located in the middle and upper reaches of the Huaihe River plain.The basin is densely populated and in serious water shortage.The average per capita water availability in the basin is about one fifth of the China average.In recent years,rapid development of industry,agriculture,and urbanization enhanced water shortage and serious water pollution in the basin and further reduces the availability of water resources.To meet the increasing water demand,deep aquifers in the basin were exploited which results in larger cones of depression in many areas of the basin and the redistribution of surface water and groundwater.Thus,it is ergent to investigate the interaction between surface water and groundwater in order to better manage water resouces in the basin.In this study the surface hydrological model PRMS was calibrated and validated first.The calibration period is from Jan.1 of 1964 to Dec.31 of 1965 and the validation period is from Jan.1 of 1962 to Dec.31 of 1963.The calibrated and validated model was then used to simulate the impacts of urbanization and dam construction on river runoff in the Shaying River basin.The results shown that both evaporation and infiltration decreased and runoff increased in the basin due to the expansion of impermeable land surface as a result of urbanization.The effects of dams are to reduce the peak flow and delay the peak flow time.Existence of dams in the basin changed the space-temporal distribution of river water and damp natural variability of the river flow but increased the area of surface water bodies and thus decreased the river runoff.The impacts of urbanization and dams on runoff are more significant in dry years.Thirdly,the conceptual model of the groundwater flow in Shaying River basin was built based on the basin's hydrologeology conditions and was simulated with MODFLOW-2005 in the GSFLOW.Finaly,the GSFLOW model which includes a surface water model and groundwater model was calibrated and validated.The results shows that the simulated values of the surface runoff and groundwater levels matched well to the observed ones.These results can be used to analize the interaction between the surface water and groundwater in Shaying River basin.The simulation results of GSFLOW shown that the water input to the basin is precipitation and the outputs are mainly evapotranspiration,surface runoff,and discharge from groundwater constant head boundaries.Most of the outflow is due to evapotranspiration and surface runoff which includes overland flow,interflow,and base flow.The surface runoff consists of maily interflow,then overland flow and baseflow.The larger the precipitation,the larger the overland flow in the basin.The soil zone is influenced by precipitation and evapotranspiration.In general,groundwater discharge to the soil zone may occur at any time of a year and has little fluctuation.A large amount of discharge to the soil zone occurs in September and October of a year generally.The groundwater in the basin is recharged by the soil zone which occurs in July and August of a year.Groundwater in the basin discharge to the rivers in Shaying river basin in most time of a year,but from June to Semtember,heavy rains may cause high water levels in the rivers and lead the river to recharge groundwater.The amount and time period that rivers discharge to groundwater have been increased,but in wet year discharge from groundwater to rivers has been reduced.