| Soil water is one of the most important water resources,and has a close relationship with groundwater,especially in the areas or seasons where groundwater table was shallow.In recent years,more and more researches show that to accurately assess groundwater recharge,it is necessary to take into account the relationship between soil water and groundwater in movement.The water-bearing layers in the Dagu River Basin are distributed mainly in a long and narrow strip of area alongside the middle and lower reaches of the Dagu River,forming a huge underground reservoir,which is one of the major water sources supplying water to Qingdao.Currently,the groundwater resource in the Dagu River Basin has been over-exploited causing a series of environmental problems,like seawater intrusion,surface subsidence,etc.With rapid development of the economy and population in the region,the problem of water resource shortage significantly constrain sustainable development of Qingdao.To enhance comprehensive management of the water resources in the region,it is essential to accurately assess groundwater recharge.Although much work has been done on groundwater recharge,few of the relevant researches have taken into account the transformational relationship between soil water and groundwater,which has resulted in big gaps between the calculation of groundwater recharge and the realityThis research based on the principle of the software of HYDRUS package for MODFLOW coupled with the GIS technology,a basin-scaled(4 781.01 km~2)soil water and groundwater coupled model(SWGCM)was developed.With all the relevant data put under comprehensive consideration,including precipitation,evaporation,plant water absorption,soil texture,aquifer distribution,and soil water and groundwater related parameters,such as groundwater exploitation capacity,soil moisture content,and groundwater table,the SWGCM model was used to simulate movement of soil water and groundwater in the Dagu River Basin,and accurately assess groundwater recharge.The main conclusions are as flows:(1)According to the fitting results of soil profile moisture content and groundwater level,the SWGCM model can be used to accurately simulate spatio-temporal variation of the soil water and groundwater in the Dagu River Basin.In the validation phase,the fitting results of the winter wheat period were significantly better than the summer maize period,mainly because the precipitation and evaporation were less in the wheat period.(2)The fitting of soil profile moisture content and groundwater table indicates that the SWGCM model is good enough to simulate the groundwater recharge in the Dagu River Basin with quite high reliability and accuracy.In the calibration phase,the groundwater recharge is 315 million m~3,the groundwater storage increases 182 million m~3,and in the validation phase,477 million m~3,the groundwater storage increases 91million m~3.It can be seen that the groundwater recharge mainly comes from the flood season.The groundwater recharge is relatively close to the results of the evaluation of the underground reservoir in the Dagu River Basin in the 1980s.(3)Maintaining existing industrial agriculture layout unchanged,in the wet year(with 809.3mm of total precipitation),the groundwater recharge is 509 million m~3,the groundwater storage increases 124 million m~3,the groundwater storage is very abundant in Dagu River Basin and has great exploitation potential;in the medium year(with 636.2mm of total precipitation),the groundwater recharge is 447 million m~3,the groundwater storage increases 65 million m~3,the existing groundwater exploitation is relatively appropriate,and the goverment should maintain the present situation of groundwater exploitation;and in the dry year(with 495.8mm of total precipitation),the groundwater recharge is 381 million m~3,and the groundwater storage increases 4 million m~3,the groundwater overexploitation is very serious,and many results indicate that excessive exploitation of groundwater in the dry year does not profit environment protection and long term economic or social benefit,the exploitation of groundwater in the dry year should be clamped down or strictly restrained.All of these indicated that the SWGCM model may provide certain scientific basis for development of a rational allocation of water resources of the basin and an effective approach,too,to accurate assessment of groundwater recharge. |
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