Land Use Change Impacts on Dynamic Sediment Connectivity in an Urbanizing Region

Sediment connectivity is defined as the transfer of sediment between landscape components from source to sink as the result of structural and dynamic watershed features. Connectivity theory has recently been formulated through a probabilistic lens as the intersecting probabilities of hydrologic and geomorphic processes, including sediment availability and erosion, hydrologic detachment and transport, and disconnectivity. As natural and rural landscapes urbanize to accommodate population growth and migration patterns, the impact of this land use change to sediment connectivity remains uncertain. To test the impact of urbanization on sediment connectivity, we apply the Soil Water Assessment Tool (SWAT) and the Probability of Connectivity Model to five watersheds in a rapidly urbanizing region of Kansas, USA. The five study watersheds have similar geomorphologic and climatologic properties, but differing urban land use (from 21% to 89%), making them ideal for isolating the impacts from urbanization on sediment processes. SWAT results indicate satisfactory hydrologic model performance with daily streamflow KGE values ranging from 0.47 to 0.85. Connectivity modeling results indicate higher degrees of sediment connectivity in rural watersheds compared to urban watersheds. In the most-rural basin, the wettest day of the study period resulted in the connection of 51% of the watershed area compared to just 31% in the most-urban watershed. The driving factor for this discrepancy was the complete disconnection of sediment supply in urban basins as a result of impervious surface cover. However, while less of the urban basin area was connected, strong connectivity was observed near the many artificial drainage pathways, such as roadway ditches, constructed in urban basins. As large portions of the Earth continue to urbanize, it is of the upmost importance that watershed stakeholders consider how land use change alters the probability of sediment connectivity so as to maximize the benefits from environmental management.