Shallow Groundwater Response to Rainfall Infiltration in Modern Yellow River Delta

Modern Yellow River Delta (MYRD) is one of the largest deltas in China. The economic prosperity increases the population in this area. However, fresh water resource is still in acute shortage. For one thing, the runoff of the Yellow River, which is the main source of fresh water, decreases year by year due to the increasingly large-scale irrigation in the upper reaches. For another, the shallow groundwater in this area mainly consists of brackish water and saline water that cannot be used directly. Lack of fresh water not only hinders economic performance but also threatens way of life. Therefore, the study on groundwater policy is of scientific value and practical significance. The water table is generally considered to be the upper boundary to saturated groundwater flow, so it plays an important role in many groundwater research projects. Groundwater policy reflects the change of quantity and quality of groundwater resource and is meaningful to sustainable development. Precipitation recharges the shallow groundwater directly and is regard as an important source of fresh water in MYRD. The research of groundwater response to rainfall can improve our understanding of groundwater policy mechanism, and is the precondition to evaluate and exploit groundwater resource rationally and to find ways to ease the freshwater crisis in MYRD. Based on data loggers installed in the boreholes in typical topography areas of MYRD, the depth of groundwater table and the temperature were read every thirty minutes with one of those loggers reading EC value at the same time from May 2004 to May 2005. The daily rainfall data were collected to study the process and features of shallow groundwater response to rainfall and to understand the mechanism of groundwater policy. We reached below conclusions: 1) the lothological differences between deposits resulted in distinctive types of groundwater policy. The infiltration- evaporation type can be defined by sediments on floodplains face and the infiltration-runoff-evaporation type can be observed in sediments on fluvial face. Precipitation was the main factor contributing to the rising of shallow groundwater level. 2) The temperature of shallow groundwater was mainly influenced by the air temperature; however, when daily rainfall was above 10 mm in rainy season, groundwater temperature could be increased by 0.3℃ averagely. 3) The EC values of shallow groundwater would begin to response to precipitation when cumulative rainfall was up to 300 mm. Precipitation could dilute shallow groundwater temporarily.