Modeling linkages between erosion and connectivity in an urbanizing landscape: a coupled sensing, geomorphometric, and field assessment approach

Abstract:

Erosion and connectivity are spatially varied processes key to determining sediment transport and delivery to downstream waterbodies. However, we find few studies that explicitly model the linkages of where erosion and connectivity coincide and where they contradict, particularly in urbanizing settings. In this study, we couple in-stream aquatic sensing, the Revised Universal Soil Loss Equation (RUSLE), Index of Connectivity (IC), and the Sediment Delivery Ratio (SDR), in conjunction with Monte Carlo uncertainty analysis, to generate a new Erosion-Connectivity Mapping (ECM) framework. We utilize the ECMs to assess coupling and (de)coupling of erosion and connectivity processes and evaluate ECM accuracy with field assessment of thirty-five sites. We apply this model to five lowland watersheds in Johnson County, KS, USA, with urban land use ranging from 21% to 89%. Erosion modeling results indicate high risk areas near streambanks and roadway systems with similar patterns in connectivity modeling. Our two connectivity measures, SDR and IC, were positively correlated at the five sites (R² = 0.80, p < 0.05) with the highest SDR in the most urbanized watershed. The ECM framework results indicate that, on average, only 3±2% of the study area is highly erodible and highly connected. In contrast, the vast majority (62±2%) of the land is poorly erodible and poorly connected. Much of the landscape is highly connected but poorly erodible (31±2%), and the remaining land is highly erodible, but poorly connected (3±2%) indicating that erosion is more likely to be the limiting factor in sediment transport. Our field assessment provides broad support for the ECMs in accurately modeling coupling and (de)coupling of erosion and connectivity; however, geospatial modeling does not accurately represent areas containing riparian buffers and anthropogenic subsurface flow paths. Further, field assessment indicated that geospatial modeling underpredicts how closely coupled erosion and connectivity are in the field and we suggest that future models consider this coupling more explicitly. This study provides a method for combining RUSLE and IC in a new tool (ECM) to identify spatial patterns in sediment erosion-connectivity and to create a unified model to aid in the understanding and management of watershed sedimentation.