| Abstrakt: |
Surface water and ground water is a unified whole in the water circulation system, and there is a close relationship between them. Especially in the areas where karst surfaces such as drop holes and funnels are developed, surface water and groundwater can form a direct connection. The interactions between surface water and groundwater have been a hot topic in research. A great deal of research has been carried out both nationally and internationally. The SWAT-MODFLOW coupling procedure developed by Seonggyu park and Ryan T. Peley is a beneficial tool for studying surface-groundwater interactions. This coupling procedure establishes the link between the Hydrological Response Unit (HRUs) in SWAT model and the spatial grid in MODFLOW through the ARCGIS platform in order to achieve a loose coupling of the model. A number of applications of this program have been carried out abroad. However, no relevant studies have used this procedure to achieve model coupling in different ranges of surface and subsurface. As far as the actual situation is concerned, often the plains are the focus of extraction and their groundwater dynamic field needs to be detailed delineated. However, the scope of SWAT model covers the overall basin, which is not consistent with the scope of groundwater flow model. Considering the running time and the accuracy of the model, it is necessary to explore the model coupling process in different ranges of surface-groundwater. In this study, the SWAT-MODFLOW coupling program of Seonggyu park and Ryan T. Bailey was used to implement the coupling of models at different scales of the surface and subsurface, and to investigate the differences between the groundwater recharge calculated in SWAT and that calculated in the MODFLOW grid output of the coupling program. Then the advantages of the coupling program for relevant studies on surface water and groundwater were analyzed. Taking this coupling procedure model of the Little River Watershed (LRW) in southern Georgia, USA as an example, this study selected Sub-basin 104 divided by the SWAT in the model as the boundary, and built the groundwater flow model with GMS10.4 based on the data of the original example model. According to the coupling model manual, ARCGIS platform and EXCEL platform, four link files required by the coupling model were completed: swatmf_dhru2grid, swatmf_dhru2hru, swatmf_grid2dhru, and swatmf_river2grid. A coupling model of Sub- basin 104 water flow model and the overall SWAT model was further developed, and the format of the model output results was controlled through its link files. On the basis of calculation results of the model, its multi-year equilibrium condition was calculated in EXCEL to judge its rationality so that the model can be calibrated. After the calibration, the accuracy of each equilibrium item was compared between the coupling model and the independent groundwater flow model. Study results show as follows. (1) The coupling procedure enables the coupling of the SWAT model naturally bounded by the surface watershed with the small-scale MODFLOW model divided by the sub-basin boundary. However, because the grid boundary of the groundwater flow model and that of sub-basin cannot be completely matched, there is a difference between MODFLOW and SWAT in terms of the calculation of rainfall recharge for groundwater. In general, the calculation volume of SWAT is larger than that of MODFLOW grid. The calculations clearly indicate that the error margin becomes smaller as the grid gets smaller because the smaller the grid area is, the more exact the match between the grid and the boundary becomes. (2) Each equilibrium item has changed after coupling. Because the river depth in GMS is taken as the empirical value, and it is taken as the confluence evolution value in SWAT, calculations show that the groundwater recharge of the river before and after the model coupling is significantly different, and the total recharge from the river to the groundwater reduces to 15.25% of that before the coupling. On the other hand, the total discharge from groundwater to river increases 19.29% after coupling. The rainfall recharge of the model before coupling is calculated by infiltration coefficient method, and the groundwater recharge after coupling is the seepage of the soil bottom of the SWAT model. The calculations show that the total rainfall recharge increases 17.07% after coupling. The groundwater evaporation before model coupling is calculated by the Avyanov formula, and the groundwater evaporation after coupling was calculated according to the potential evapotranspiration and the actual evapotranspiration calculated by SWAT. The calculations show that the total evapotranspiration is 3.08 times larger than that before coupling. It is found that the coupling model can simulate the surface-subsurface hydrological process more accurately, and can reflect the relationship between precipitation and groundwater, surface water and groundwater transformation. [ABSTRACT FROM AUTHOR] |
