Effects of roads on hydrology, geomorphology, and disturbance patches in stream networks

We propose that road network effects on flood flows and debris flows modify disturbance patch dynamics in stream and riparian networks in mountain landscapes. We outline a view of how road networks interact with stream networks at the landscape scale, and illustrate how these interactions might affect biological and ecological processes in stream and riparian systems, using examples from recent and current research. At the landscape scale, certain definable geometric interactions involving peak flows (floods) and debris flows (rapid movements of soil, sediment, and large wood down steep stream channels) are produced by the arrangement of the road network relative to the stream network. Although disturbance patches are created by peak flow and debris flow disturbances in mountain landscapes without roads, roads can alter the landscape distributions of the starting and stopping points of debris flows, and they can alter the balance between the intensity of flood peaks and the stream network's resistance to change. We examine our conceptual model of road network - stream network interactions based on evidence from a number of studies in the H.J. Andrews Experimental Forest, Oregon. We speculate that road network effects upon the spatial pattern of disturbance may influence the rates and patterns of survival and recovery of disturbed patches in stream networks, affecting ecosystem resilience, and we outline an approach for detecting such effects.