Numerical modeling of effects of small‐scale sedimentary variations on groundwater discharge into lakes

The effect of small‐scale sedimentary structural variations (on the order of a few tens of centimeters) on groundwater‐lake interaction is investigated with CROSSFLO, a finite‐element model that simulates two‐dimensional steady state flow in cross section via stream functions. Simulations show that relatively thin continuous or discontinuous layers can strongly influence migration paths, recharge‐discharge profiles, flowline inclinations at the sediment‐ water interface, and travel times. In the case of groundwater‐mediated contamination of lakes from sources located on land, results show that the presence of thin layers can change the point of contaminant entry into a lake by several hundreds of meters. Further, time required for the contaminants to reach the lake may be altered by decades or centuries. These results stress the importance of detailed description of subsurface geology for realistic predictions of contaminant migration from groundwater into lakes and for sound lake management.