A comprehensive discrimination method for the genetic type of groundwater regime of phreatic water: a case study in the Songhua River basin of the Sanjiang Plain

Traditional methods for discriminating the genetic type of groundwater regime have some problems, such as being substantially affected by human subjective factors and the ease of producing multiple solutions. To improve the discrimination reliability of the genetic type of groundwater regime, this study proposes a comprehensive discrimination method combining a qualitative analysis of hydrogeological conditions and quantitative analysis of measured data. Firstly, according to the meteorological, hydrological, and hydrogeological conditions of the study area, the effects of various groundwater recharge and discharge items on groundwater regime are quantified. Then, a correlation analysis and logical judgment are carried out based on the dynamic data. The recharge and discharge items that contribute the most to the groundwater regime are identified, and the genetic types of the groundwater regime are named and determined accordingly. Based on this method, this study uses the same 57 groundwater observation points in the Songhua River basin of the Sanjiang Plain as in 2011 and 2015. These data were combined with the groundwater level depth, groundwater level, river water level, precipitation, distance from the observation well to the river, and lithology of the unsaturated zone. The genetic types of the groundwater regime in the study area were divided into six types: hydrological type, precipitation infiltration type, precipitation infiltration-evaporation type, precipitation infiltration-runoff type, precipitation infiltration-exploitation type and exploitation type. Comparing the changes in the genetic type of groundwater regime of the study area from 2011 to 2015 revealed thatthe proportion of natural genetic types, such as precipitation infiltration type and precipitation infiltration-runoff type, decreased, whereas the proportion of the genetic type affected by human activities increased. This indicated that the impact of human exploitation activities on the groundwater regime is increasing. Compared with the traditional qualitative analysis method based on the characteristics of the groundwater regime curve, the comprehensive discrimination method proposed in this study can identify the driving factors of groundwater regime, while fully considering the hydrogeological conditions and combined with quantitative methods, which improves the scientific reliability and work efficiency of the discrimination of the genetic type.