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Representing the Connectivity of Upland Areas to Floodplains and Streams in SWAT+

Katrin Bieger, Jeffrey Arnold, Hendrik Rathjens, Michael White, David Bosch, Peter Allen
Journal of the American Water Resources Association 2019 v.55 no.3 pp. 578-590
Soil and Water Assessment Tool model, floodplains, highlands, landscapes, pollution, rain, runoff, soil water, stream flow, streams, watersheds
In recent years, watershed modelers have put increasing emphasis on capturing the interaction of landscape hydrologic processes instead of focusing on streamflow at the watershed outlet alone. Understanding the hydrologic connectivity between landscape elements is important to explain the hydrologic response of a watershed to rainfall events. SWAT+ is a new version of the Soil and Water Assessment Tool with improved runoff routing capabilities. Subbasins may be divided into landscape units, e.g. upland areas and floodplains, and flow can be routed between these landscape units. We ran three scenarios representing different extents of connectivity between uplands, floodplains, and streams. In the first and second scenario, the ratio of channelized flow from the upland to the stream and sheet flow from the upland to the floodplain was 70/30 and 30/70, respectively, for all upland/floodplain pairs. In the third scenario, the ratio was calculated for each upland/floodplain pair based on the upland/floodplain area ratio. Results indicate that differences in streamflow were small, but the relative importance of flow components and upland areas and floodplains as sources of surface runoff changed. Also, the soil moisture in the floodplains was impacted. The third scenario was found to provide more realistic results than the other two. A realistic representation of connectivity in watershed models has important implications for the identification of pollution sources and sinks.