Estimation of Recharge in Karst Systems from Spring Hydrographs

A time-continuous approach for the estimation of recharge in karst aquifers is presented, which does not require any information about the characteristics of the unsaturated zone (Geyer et al. 2008). The approach is based on time derivative(s) of spring hydrographs and recession coefficient(s) of reservoirs. The first time derivative of the discharge curve of a reservoir reflects the temporal distribution of inflow and outflow from the reservoir. The recession coefficient of a reservoir determines the velocity with which a recharge signal is transmitted through the reservoir, i.e. it reflects the hydraulic diffusivity (ratio of transmissivity and storativity). Karst aquifers can be described as dual flow systems consisting of the conduit system and the fissured matrix. As shown in principle studies with a serial two-reservoir model, rapid recharge in the conduit system clearly dominates the early response of spring hydrographs even if the fraction of the rapid recharge component is only a few percent of total recharge. This behavior can be attributed to the large contrast between recession coefficients of the conduit system and of the fissured matrix. It allows the separation of the rapid recharge component after recharge events in karst aquifers. The methodology has been applied to estimate the temporal distribution of rapid recharge in the conduit system of the karst aquifer Gallusquelle (Swabian Alb, Germany). The results reveal the importance of rapid recharge after rainfall events as well as snowmelt events.

T. Geyer, S. Birk, R. Liedl, M. Sauter (2008): Quantification of temporal distribution of recharge in karst system from spring hydrographs. Journal of Hydrology 348: 452-463.