Study On Surface-water And Groundwater Interactions In Typical Gneiss-mountains Watershed

With the influence of climate change and human activities, the interaction of regional surface water and groundwater is more and more frequent, in order to accurately grasp the impact of human activities on regional water cycle rules, it is necessary to study the surface water and groundwater as a whole system.Muzhu River Basin in Weihai is located in the North China platform, the axis of Shandong anteklise Jiaodong convex. The basin outcropping strata are mainly pre Sinian metamorphic rocks, forming anticline base by gneiss, schist, phyllite. The main groundwater types are bedrock fissure water and Quaternary porous water. Bedrock fissure water occurs mainly in the gneiss and granitic gneiss weathered fissure. The Quaternary porous water is mainly distributed in the mountain valley plain and coastal plain and blunt pluvia and marine sediments of fine sand, silt and fine sand strata. The groundwater table is shallow in the basin, water rich aquifer is weak and river network is dense, which makes it easy to produce complex surface groundwater interaction process in the intense and frequent rainfall conditions.In this paper, the interaction between surface water and groundwater is studied by the surface and subsurface flow coupling model GSFLOW(coupled Ground-Water and Surface-Water flow model based on the integration of PRMs and modflow-2005) package. Based on the analysis of the Muzhu river watershed hydrologic meteorological and hydrological conditions, regional geological background, hydrogeology, water resources and its exploitation and utilization situation, the study have structured the coupling model of the surface hydrology simulation model(PRMS) and the groundwater flow numerical simulation model(MODFLOW), and have carried out hydrological data and geological data mining, and hydrogeological data mining, model calibration and verification, Simulate and analysis the groundwater and surface water interactions under different precipitation conditions and different mining conditions. The results show that:(1) Gneiss-Mountains Watershed, because of the special geological condition and hydrogeological conditions, the heavy rain makes groundwater rapidly recharged, groundwater level rise sharply, which makes the river is recharged superiorly by the process of groundwater infiltrating into shallow soil, and it leads to the relatively short storage time of the groundwater in the low permeability water medium, so the interaction between the surface water and groundwater is obvious.(2) GSFLOW can reveal the complex nonlinear process of groundwater recharge due to precipitation and the process of groundwater discharge to the soil layer and the river. The interaction between surface water and groundwater can be simulated efficiently.(3)Based on the GSFLOW principle, the coupling model of surface water and groundwater in the study area was constructed and the numerical simulation model was built implying the data of runoff station in 2008-2013 and the data of groundwater observation well. The results shows that the runoff in deterministic coefficient of the Nash model is larger than 0.65, the absolute mean error of groundwater observation well logging in the Muzhu river basin is about 0.3m, and the simulation accuracy is good.(4) By the simulation of surface water and groundwater interaction process under different precipitation conditions and groundwater exploitation scenarios, it shows surface runoff and groundwater recharge flux are both strong time variability. The greatest impact is surface runoff(Pe), and the relatively small effect is percolation beneath the soil zone(PR), gross recharge(gR), effective recharge(eR) and net recharge(nR), Within the short-term high intensity in the low permeable hard rock area, there is not able to cause a large area of groundwater recharge effectively. Influenced by the exploitation of groundwater under the same underlying surface and rainfall conditions, there is an obviously linear positive correlation between the groundwater level and the base flow.The constructed GSFLOW model can efficiently reflect the general law of the interaction between surface water and groundwater, which can be used as an effective tool for the assessment of water resources, and is of great significance for the integrated management of surface water and groundwater in the basin.