Application of gray relational method to the time-lag between spring discharge and precipitation

Karst groundwater system is a complicated system with inexact data, short sample and unclear boundary conditions. Gray theory has emerged in recent years as a new tool to deal with problems of small samples and insufficient information. In this paper, the gray relational method was applied to Jinci spring to investigate the time-lag between spring flow and precipitation. The results showed that the average groundwater residence time of Jinci spring is about 7 years. Jinci spring in north China is a system of slow-response spring. The spring discharges in Jinci spring basin lag behind precipitation by several years. A slow-response to precipitation should be considered one of characteristics of karst springs in north-China.