Using Wavelet Coherence to Characterize Surface Water Infiltration into a Low‐Lying Karst Aquifer

Karstified carbonate aquifers may receive significant recharge contributions from losing streams, hence, the knowledge about surface water‐groundwater (SW‐GW) interactions is crucial with regard to water management (e.g., source protection zone delineation). The dynamics of SW‐GW interactions may depend on factors such as the relative water levels between streams and aquifers, resulting in a temporal variation of exchange, which imposes complexity to the understanding of such dynamics. This study highlights the use of high‐resolution time series and multiresolution analysis to help to gain insights into such complex dynamics. Wavelet coherence is applied on hourly time series of rainfall, stream, and spring discharges of a low‐lying karstified spring catchment to yield a correlation in the time‐frequency domain. This analysis provides comprehensive information on the overall impact of the river on the spring, which is supported by the cross‐correlation function, as well as by more detailed information, including time‐variant influences such as a threshold level of influence. Field observations of turbidity sampling at the spring appear to support this interpretation. This innovative approach relies on basic hydrological parameters, water level, or discharge, and is therefore applicable to many other systems with such existing time series.