Efficacy of environmental site design in protecting channel stability under changing climate


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American Ecological Engineering Society


Research on the impacts of climate change (CC) on water resources has received much attention during the past decade. However, little research has been done on how future climate will likely impact sediment transport and channel stability of first-order streams, particularly in urban environments which utilize Nature-based Solutions (NbS) for stormwater management. This study aimed to assess whether the current stormwater regulations in the state of Maryland, USA, which require the use of environmental site design (ESD), are protective of channel stability when CC is considered. ESD relies on the combination of the concepts of NbS for enhanced infiltration and evapotranspiration with the utilization of storage-based gray infrastructure. To achieve this goal, a coupled hierarchical modeling approach was developed and applied to examine projected changes in bedload transport and channel geometry for a first-order riffle-pool, gravel-bed channel draining an urban watershed equipped with the extensive implementation of ESD. The modeling approach was based on discharge from a watershed-scale hydrologic model driven by a range of spatiotemporally downscaled CC scenarios. Changes in sedimentary responses of the modeled reach were estimated using the Hydrologic Engineering Center River Analysis System 6.3 (HEC-RAS). Ensemble simulation results showed that even with the extensive implementation of ESD, the studied reach is expected to degrade over many decades developing alternate regions of aggradation and degradation due to the changes in watershed hydrology caused by urbanization under both current and future climate conditions. Mobilization of larger particles during high-magnitude storm events and their subsequent deposition upstream of narrower sections of the reach leads to the formation of several steep riffles. Results from this study show that the current stormwater regulations in the State of Maryland are not protective of channel stability and that changes in climate will likely accelerate channel degradation.