Thinking outside the channel: Challenges and opportunities for protection and restoration of stream morphology in urbanizing catchments

• Stream restoration goals may be better achieved working with geomorphic processes.
• Feasibility in an urban context requires addressing the causes not symptoms.
• We discuss addressing stormwater runoff, riparian space and sediment loads.
• Legacy land use and social/institutional barriers require greater consideration.

Urbanization of catchments profoundly changes the morphology of streams by increasing stormwater runoff, altering sediment regimes, and limiting space for channel change. Management response commonly involves addressing the symptoms of urbanization by reconfiguration and partial hard-lining of the channel. Mounting evidence suggests, however, that stream restoration goals may be better achieved by addressing the causes of channel degradation at a catchment scale, increasing opportunities to work with geomorphic processes. The challenges of this approach in urban catchments have not been comprehensively explored. In this perspective essay we describe how stream restoration in urban catchments might be better achieved by undertaking activities in the catchment or riparian zone to address the causes, rather than patch the symptoms. We describe the challenges that need to be overcome to address these causes including; excess stormwater runoff, lack of riparian space, altered sediment supplies, legacy impacts on streams from former land use, and social and institutional barriers. We discuss opportunities for each. A more sustainable urban stream solution may be achieved by addressing these issues to reduce the impact of urbanization on stream morphology.