Response characteristics of groundwater level dynamics to precipitation based on continuous wavelet-cross correlation analysis:A case study of the Guiyang karst basin
Precipitation is the main source of water supply for most groundwater systems;therefore,its spatiotemporal distributions will,to some extent,determine the dynamic characteristics of groundwater levels.Hence,conducting research on groundwater level dynamics is of great significance for the sustainable development and utilization of groundwater resources,regulation and management of surface-groundwater resources,and determination of floating resistance and anti-floating water levels in engineering construction.The Guiyang karst basin is located within the construction scope of the main urban area of Guiyang City.In order to further understand the nonlinear process of groundwater level dynamics in the karst basin area,and help improve the management of groundwater resources in this area,we collected the observation data and precipitation data of seven observation points of groundwater levels in the Guiyang karst basin in different periods from 2007 to 2021.Besides,to analyze the groundwater level dynamics on different time scales and the response of the dynamics to precipitation in the Guiyang karst basin,we adopted the continuous wavelet analysis that can quantitatively judge the periodicity of precipitation and groundwater levels,and the correlation analysis that can quantitatively calculate the lag relationship between groundwater and precipitation.The results show as follows.(1)According to the groundwater level data from monitoring holes in the study area,the water level variations of the monitoring holes located inside the Guiyang karst basin is relatively small,with a maximum annual water level variations of about 2-7 m,because this basin,featuring relatively flat terrain,is a discharge area of the groundwater system.The edge of the Guiyang karst basin is controlled by the terrain and topography,with significant undulations.The water levels of monitoring holes located at the edge of the basin vary greatly,with the maximum variations of water level about 10-20 m over the years.In terms of the continuous wavelet transform analysis of the response characteristics of groundwater levels to precipitation in the study area,it can be concluded that the main oscillation period of precipitation is 256-512 days,which passed 95%of the red noise tests from January 2008 to January 2017,indicating significant periodic characteristics.Due to the influence of hydrogeological conditions and human activities around monitoring holes,the oscillation periods of different observation points varied.However,the groundwater level dynamics in the Guiyang karst basin were significantly controlled by precipitation,showing discontinuous and short oscillation periods in high-frequency areas,with an overall main oscillation period of 256 to 512 days.(2)In the study area,there is a significant time lag between groundwater level variation and precipitation.That is,the longer a groundwater runoff distance is,the more hysteretic the response of groundwater level to precipitation becomes.The groundwater level variation in the runoff-discharge area lags behind precipitation by 2.66-7.7 days,by 1.25-8.04 days in the discharge area.Because the regional hydrogeological conditions of the two groundwater systems in the study area are different,the responses of the two groundwater systems in the north and south to precipitation are also different.In the southern groundwater system,the time lag of the response of groundwater level variations to precipitation gradually increases from the runoff-discharge area to the discharge area.In the northern groundwater system,due to the effect of the long-distance precipitation recharge from upstream,the groundwater level of runoff-discharge area changes more slowly than that of discharge area with multiple sources of recharge.
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