Sediment dynamics of watershed urbanization and river restoration: Insights from 10 years of research in small gravel-bed rivers

Abstract

Watershed urbanization frequently leads to river channel enlargement and incision. Mitigation strategies such as in-channel restoration and stormwater management have been developed to counteract these problems, yet alternatives are rarely considered with respect to the sediment dynamics that underlie the process of river degradation. In the current paper, we revisit two heavily urbanized small gravel-bed rivers where aggressive stormwater management and river restoration projects were completed. The goal is to consider how information from 10 years of research on sediment dynamics might change the adopted mitigation strategies. By synthesizing previous work and novel analyses, we provide a diagnosis of the effects of urbanization and existing restoration efforts on the channel morphology and sediment dynamics and develop a sediment augmentation strategy to restore the dynamic equilibrium of the study reach. Additionally, we model the cumulative impact of various stormwater management strategies on sediment dispersal. We place these river management strategies within a framework that seeks to address the root cause of urban river degradation by rebalancing the sediment supply and capacity of these channels.