Research on the response mechanism of groundwater level to rainfall in the western suburb of Jinan based on wavelet analysis

ZHAO Zhenhua; LUO Zhenjiang; HUANG Linxian; XING Liting; LI Hongtao; SUN Hongjie

doi:10.11932/karst20230506

Abstract：With the rapid development of social economy,karst groundwater in Jinan City keeps facing various problems such as water resource shortage and water pollution,which seriously threatens the protection of springs and the utilization of groundwater resources.The western suburb of Jinan City is located at the northeast edge of Jinan spring catchment;the Yufu river and Shahe river abundant in groundwater are important recharge sources for Jinan spring catchment.Therefore,it is very important to accurately reveal the response mechanism of groundwater to precipitation in the western suburb,which can help to improve the potential of groundwater exploitation and spring protection.In this study,the monthly precipitation data from 2010 to 2019 in the western suburb of Jinan City and the monthly water level data of Quaternary and karst groundwater are used to carry out seasonal statistical characteristics and wavelet analysis. Results show that,(1)According to the seasonal statistical characteristics of precipitation and groundwater,the precipitation in the western suburb of Jinan City mainly concentrates in summer,accounting for about 67.5％of the annual precipitation.The groundwater level is the highest in autumn,with the average water levels of the Quaternary and karst being 30.28 m and 29.74 m,respectively.The groundwater level is the lowest in spring,with the average water levels of the Quaternary and karst being 29.44 m and 28.78 m,respectively.Seasonal fluctuation of groundwater dynamics in the study area is the coupling effect of human and natural factors.Since the beginning of spring in March,precipitation has decreased and the amount of evaporation has increased along with the rise of temperature.At the same time,a large amount of groundwater has been extracted for agricultural irrigation,resulting in a drop in the groundwater level.Although the precipitation is relatively abundant after the beginning of summer,the infiltration of precipitation into the aquifer has a certain lag(generally about 2-5 months),resulting in the fact that the highest groundwater level occurs in autumn.(2)Through continuous wavelet transform analysis,it can be concluded that the main oscillation period of precipitation is 0.98-1.17 a and it passed the 95％red noise test from April 2011 to October 2018,indicating that it has significant periodic characteristics.The main oscillation period of Quaternary groundwater is 0.73-1.16 a and 1.17-1.74 a and it passed the 95％red noise test from April 2011 to January 2015.The main oscillation period of karst groundwater is 0.87-1.09 a and 0.46-1.23 a,but it passed the 95％red noise test only from March 2013 to October 2014 and from June 2016 to October 2018.The main oscillations periods are not completely consistent with groundwater level and precipitation,reflecting that the dynamics of groundwater in the study area is not only affected by precipitation,but also by other factors such as human activities.(3)Cross wavelet transform analysis shows that the main resonance period of precipitation and groundwater level is about 1 year.The groundwater level dynamics of Quaternary and karst aquifers lag behind precipitation by 144.14 d and 172.62 d,respectively,with the difference of only 28.48 d,which may reveal that the hydraulic connection between Quaternary and karst aquifer is very close.The dynamic curves of the Quaternary and karst groundwater level show that the dynamic changes of the two are relatively consistent,although the dynamics of the karst groundwater level lags behind,but with relative short lagging time,which further indicates that these two aquifers have a good complementary relationship.In addition,the drilling data of monitoring wells in the study area show that there is no obvious water-resisting layer between the Quaternary and the karst aquifer,and the karst aquifer has well-developed fissures,strong water-abundance,and is cut by faults,with strong water-conducting capacity.All the above results show that the response of groundwater level to precipitation is significant and stable.