The Hysteresis Response of Groundwater to Reservoir Water Level Changes in a Plain Reservoir Area

Reservoir immersion will lead to some environmental geological problems, such as soil swamping or salinization, reduction of building foundation strength, or even overall instability. Reservoir scope of immersion is closely related to changes in groundwater levels. According to the geological and hydrogeological conditions pertaining in the Jiangxiang reservoir area, the analytical method is employed to calculate the change in groundwater levels in an unconfined aquifer when the reservoir water level rises rapidly to a constant value and changes periodically. Combined with the related functions of MATLAB™ software, the lag and immersion times are determined in different locations around the reservoir. The results show that the change of the groundwater level exhibits hysteresis relative to that of the reservoir water level owing to the low permeability of silty loam and clay. The closer to the reservoir, the faster the groundwater level rises or falls. In the Guo Xiaoxu section, when the reservoir water level rises rapidly to 42.5 m, the groundwater level near the reservoir remains lower than the reservoir water level after 50 years. If the hydraulic conductivity is increased by three orders of magnitude, the groundwater level and the reservoir water level changes are positively correlated, and the hysteresis is not obvious. In the crop areas, the scope of immersion in the Guoxiaowei section is 31 m with the immersion elevation of 43.23 m, and the corresponding immersion time is 15,766 d. In residential areas, the scope of immersion of the Qigang section is 308 m with the immersion elevation of 46.78 m, and the corresponding immersion time is 16,354 d. The calculated scope of immersion and time at different locations provide a scientific basis for the design of the reservoir water level and the range of demolition affecting local residents.