| The main characteristics of hydrology in the Jianghan-Dongting Plain are widely distributed surface water and shallow groundwater. Moreover, surface and ground water interactions are very frequent as the existing of several rivers like Changjiang, Hanjiang, Xiangjiang, Zishui, Ruanjiang and Lishui, and also 330 lakes including Dongting lake, Honghu lake. Also, human activities like the constructions of Three Gorges Dam, the middle Route Project of S-N Water Transfer, and extensive groundwater extractions, which have caused an extremely frequent exchanges between surface and groundwater, and further made a lot of geo-environmental problems like land subsidence, groundwater pollution, and decreasing of groundwater levels in this region. It is essential to develop a coupled model of watershed hydrological model and groundwater numerical model and to calculate the exchanging volumes for a rational use of water resource and environmental protection.This study considered the characters and shortages in dispersed watershed hydrological model and the groundwater numerical models, discussed different methods of coupling models for surface and groundwater system. We input the regional meteorological, geological, hydrological and monitoring data into the constructed model, which was then evaluated by data of surface runoff and groundwater level. A scheme was proposed to predict the changes of surface runoff and groundwater level in the case that the upland has a constant flow. The main conclusions of this study are including:(1) This study constructed a surface/groundwater coupled mathematical model based on the SWAT model and numerical model of groundwater.The hydrologic response unit (HRU) for a surface water model and Cell of groundwater model was matched so that the hydrologic factors calculated by surface water model, including the infiltrating recharge, the evaporation, the exchanges of the river and groundwater can be transferred to the corresponding computing unit of groundwater. Considering the discretion law of HRU and the possibility that one HRU could fit several hydrological parameters, the hydrological parameters weighted average method was proposed in this study, through which we can transfer the physical quantities such as rainfall infiltration, evaporation, discharge to the corresponding cell grid of the groundwater model. This method can improve the weakness of the classical average distribution method. Based on the code of the SWAT model and MODFLOW model, this study designed a program of the coupling model by Fortran language. This program can realize a completely coupling of two computing processes, one is for the SWAT model and the other is for MODFLOW model. This coupling method can overcome the difficulties caused by the transferring of the intermediate data by GIS.(2) A coupled numerical model for surface water and groundwater in Jianghan-Dongting plain was constructed by using the coupled numerical model and software.This study extracted several parameters like hydrology and meteorology, soil, land use, which are required by coupled model. The digital river network based on DEM database was obtained by GIS and RS. The study region was divided into 105 subbasins by using 50 km2 as the threshold. The combinations of land use maps, soil type maps and slope partition were analyzed. A total of 676 hydrological response units (HRU) were divided. The rainfall and temperature data from many monitoring sites were input to the coupling model in order to simulate the daily runoff in the studying region from 2010 to 2013. Also, the sensitivity of parameters was tested and determined for a calibration. At last, the coupled model is calibrated and corrected referring the measured outlet flow data of the main rivers in the region. The hydrological process in the studying region was modeled by using the built coupling model. Our results showed that the coefficients between predicted and tested value in several Stations we selected from 2012 to 2013 are all greater than 0.6, with the modeling Nash-Suttclife deterministic coefficients are all greater than 0.5, which indicated a pretty good predicting power.(3) Water resource of Jianghan-Dongting plain was evaluated by the above constructed coupled numerical model.The hydrological process from 2010 to 2013 was simulated using the calibrated and corrected model above, and monthly runoff components were output. Through analyzing the proportion of runoff components, it is displayed that surface runoff and base flow occupied the majority of the total runoff and lateral flow occupied a very small proportion. Also base flow component is relatively stable. The annual fluctuation is very small and only a moderate ups and downs change in the high water period. However, base flow occupied the most of the total runoff in dry seasons.Averaging hydrological accounting was obtained from 2010 to 2013 simulated by the coupled model. The monthly averaging precipitation is 99.32mm, surface runoff is 26.88mm, which occupied 27.06% for precipitation. Increment from soil to groundwater is 14.91mm, which occupied 15.01% for precipitation, lateral flow is 0.20mm, occupying 0.21%; evaporation is 55.53mm, occupying 55.91%;water stored in soil is 1.79mm, occupying1.81% to precipitation. To sum, the evaporation is the first output in the study region, the second one is surface runoff.In generally, most coefficient value between predicted and tested water level are high which indicated a good modeling. A few sites got low efficiency because these sites are mining wells or near to mining wells. From the water balance sheet, the inflow and outflow are neatly the same in different phase during model recognizing and certification sections, which indicated that the model is astringency and stability. In 2013, the rainfall infiltration occupied 85.67% in total recharge of groundwater system, while the leakage recharge of surface water occupied 13.9%. Evaporation drainage and surface water drainage are the main two ways in the drainage in groundwater system, which occupied 44.98% and 38.69% respectively. The results indicated that a closed relations between surface and groundwater near river and lakes in the region. The model generally reflected the characters and trends of groundwater movement, which reflected the structure and functions of groundwater system in the studying region.(4) Changes of flow river and groundwater resource were stimulated and predicted in different climate conditions and different landuse methods in Jianghan-Dongting plain by the constructed coupled numeric model.This study simulated the Jianghan-Dongting plain hydrological processes according to the precipitation data in recent 30 years. Here three cases of rainfall value with the occurrence frequently of 90%、70% and 50% were selected respectively, and keeping the other parameters unchanged at the same time. Balance results of monthly mean and total runoff from 2010 to 2013 were obtained from the simulation.By changing the classification results of some area, we set two kinds of scenarios of landuse on the basis of the land-use data of 2013 using the software EN VI. This study simulated the value of runoff on the basis of nine kinds of assemblage of temperature and precipitation from 2010 to 2013, and the average annual runoff, the average variation of runoff and its rate of change were finally received. The results indicated that the runoff has close relation both with the temperature and precipitation in general. The influence of precipitation to runoff is more significant than the temperature. In general, precipitation and runoff are positively correlated, while temperature is negatively related with runoff.The main reason is that increasing of precipitation can lead to the increase of surface runoff, which then caused the increase of runoff. While the rising temperature increased evaporation of basin, which relative reduced surface runoff.The main Innovation points are followings:(1) This study pointed out the limitation of SWAT and hydrological numeric model, and proposed a new method to weighted averaging the hydrological response unit including rainfall infiltration, and evaporation discharge into groundwater numeric models. A couped model was developed using FORTRAN90 based on the models of SWAT and groundwater numeric models. The related program was written based on SWAT and numeric model.(2) A surface and groundwater model was developed for Jianghan Dongting plain, which can provide useful information and technical supports for the modification of surface/ground water system and eco-environmrntal protections in ths region. |
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