A dynamic analysis of groundwater levels in a large fractured-karst groundwater wellfield in Henan

Karst groundwater near the Qingduo wellfield is the main water supply source for the city of Jiyuan. It is of great significance to study the dynamic change characteristics of groundwater levels and the influencing factors for the rational development of groundwater resources and the protection of ecological environment. It is also of great significance to explore whether the Manghekou Reservoir is a recharge source area for the safe water supply of the city. In order to verify the replenishment effect of the groundwater after the impoundment of the Manghekou Reservoir, based on the monthly groundwater level data (from June, 1994 to December, 2019) of a large-scale fractured karst groundwater wellfield in Henan, the groundwater level dynamics at different stages and periods are analyzed. The step wise regression analysis is used to quantitatively determine the influencing factors of groundwater level dynamics in the wellfield and a stepwise regression equation for the dynamic prediction of groundwater levels is established. The results show that (1) in the first stage (before the impoundment of the Manghekou Reservoir), the groundwater levels near the wellfield are mainly affected by precipitation and mining. In the first period (from June, 1994 to December, 2005), the extraction rate of the wellfield was about 20000 m³/d, and the groundwater levels were mainly affected by precipitation. In the second period (from January, 2006 to August, 2014), the extraction rate of the wellfield was increased from 22000 m³/d to about 65000 m³/d, the groundwater levels were affected by the dual factors of precipitation and mining, showing an decreasing