An Integrated Modeling Of Variably Saturated Groundwater Flow System In Typical Area Of Dagu River Basin

The Dagu River Basin(DRB)is one of the large water supply sources in Shandong Province.In the past decades,the immoderate exploitation behavior and climate change triggered severe problem including obvious decline of the water level in Dagu River and seawater intrusion.Therefore,it is of great significance to maintain the balance between the local economic development and environmental conservation by implementing the water resources planning and management.As the critical zone between atmospheric water,soil water,plant water and groundwater,the unsaturated zone plays an important role in the groundwater system.In this study,the typical region with the intensive agricultural development in the lower reaches of Dagu River is selected to simulate the variably saturated groundwater flow system based hydrogeological data and natural climate data.The vertical unsaturated flow in the study area is simulated based on the kinematic wave approximation of Richards'equation which has been implemented in the UZF(Unsaturated Zone Flow)package of MODFLOW-2005.After building the three-dimensional geological model to understand the stratigraphic structure and aquifer system,the integrated numerical model of variably saturated groundwater flow is constructed and calibrated based the observed data of water table and soil moisture content.The study results show that the coefficient of determination between the simulated and observed groungwater level can be reached to 0.99 and the error metric is only 0.12 m.Meanwhile,the vertical variability of the hydraulic properties of the unsaturaed zone cannot be simulated in the simulation due to the limitations of the model setup,but the water content achieved by the model can describe the general distribution of water in the unsaturated zone.During the simulation period,according to the water budgets,the total water supply is 1121.22×l04 m3/a,and the total discharge amount is 736.36×104 m3/a.Additionally,atmospheric precipitation and groundwater extraction are very sensitive to the groundwater level while the unsaturated zone has a significant lag effect on the precipitation infiltration.The dynamic variation of water resources under the different groundwater pumping scenarios was predicted based on the well-calibrated integrated simulation model.The results show that the current pattern of groundwater exploitation can be sustained while the increased water demands in the future probably result in the obvious decline of groundwater level.Therefore,the water managers can maintain or slightly increase the water supply from the groundwater exploitation to satisfy the socioeconomic development while ensure the enough environmental flow for water demands of the ecosystem in DRB.