Seepage and Recharge under a Stream-aquifer Unsaturated Connection

Most widely used integrated hydrologic models use outdated descriptions of the stream-aquifer flow exchange. Understandably they do it for practical reasons to avoid computational costs in large-scale regional studies. In this article we propose a largely analytical technique that (1) describes the situation when the connection is unsaturated while avoiding a lot of numerical work and at the same time remains quite physical, (2) has the capability to describe fluctuations between saturated and unsaturated connections, and (3) can be coupled easily with the numerical groundwater model that describes what happens in the broad system of cells away from the river(s). Essentially two separate methods are compared for the purpose of selecting the most practical of the two.