Regional Variability of Stream Responses to Urbanization: Implications for Risk-Based Assessments

Predictive scientific assessments of the geomorphic consequences of urbanization must be calibrated to the regional hydroclimatological, geologic, and historical context in which streams occur. We present examples of context-specific stream responses to hydromodification, and a general framework for risk-based modeling and scientific assessment of hydrologic-geomorphic-ecologic linkages in urbanizing watersheds. The framework involves: 1) a priori stratification of a region's streams based on flow regime, geomorphic context and susceptibility to changes in water, sediment, and wood regimes, 2) field surveys across a gradient of urban influence, 3) coupling long term hydrologic simulation with geomorphic analysis to quantify key hydrogeomorphic metrics, and 4) using probabilistic modeling to identify regional linkages between hydrogeomorphic descriptors and decision endpoints of primary interest to stakeholders and decision-makers.