Conduit network structural controls on groundwater flow and solute breakthrough in karst aquifers

Abstract:

The structure of the conduit network is a key factor that governs flow and transport behavior in karst aquifers. The network inlet (recharge) and outlet (karst spring) locations may be known, but direct measurements of the conduit network and associated structural properties (volume fraction, sinuosity) are generally limited for the aquifer interior. This study considers the information content of indirect solute tracer data for inferring structural properties of the network. Observations from selected karst aquifers in the USA provide motivation for a numerical investigation that utilizes synthetic models characterized by a branching conduit network surrounded by permeable matrix material, with focused discharge at a single karst spring. The permeable matrix allows for solute exchange between the conduits and diffuse flow domain. Results from physics-based flow and transport simulations demonstrate how variations in conduit network geometry influence solute breakthrough at the outlet. Solute particle arrival time distributions, generated from synthetic tracer tests, are described by the mean, variance, skewness, and early (5th percentile) breakthrough times. The results indicate a clear relationship between these statistical moments and structural properties of the network, highlighting the potential signature of conduit network structure on hydrologic response and solute transport in karst aquifers.