Workshop #3   8:30 am – 12 pm (BACK)
Tuesday, July 21

Urban Stream Rehabilitation – Challenges, Differences and Mistakes

Bill Annable,  PhD, PhD, PEng, PGeo
University of Waterloo,
Waterloo, ON Canada

River rehabilitation projects in urban areas across North American are disproportionately large in numbers relative to other wilder or domesticated landscapes and terrains.  However, urban landscapes pose unique challenges stemming from changes to watershed hydrology and sediment supply/transport which are then further complicated by additional infrastructure design constraints.  Often, practitioners apply tools and methods derived from rural settings which have often lead to less than desirable outcomes requiring re-construction, increased maintenance and/or not the intended river morphology.

This workshop aims at culminating over 20 years of research and restoration practice in urban areas across North America and Europe and identifies challenges in landuse planning, common errors in field data collection, and rehabilitation design approaches.  Highlights of the issues that will be addressed will include: the hydraulic design of bridges versus morphologic stability designs, the misuse of flow frequency analyses in designs, conundrums in stormwater management approaches, limitations in strictly apply regime-theory relationships, reductions in long-term bed material supply and alterations to the transport regime (the Achilles heal of rehabilitation projects), evolving bed morphologies and the critical importance of floodplain connectivity.

Based upon performance monitoring of a series of urban restoration projects, many lessons have also been learned about the high-flow functioning of in-stream structures.  “Field tests” on several projects which have experienced storms ranging between the 75- and 300-year return frequencies have identified alterations that may be required or different in-stream structures choices to further compliment unique watershed landuses and valley configurations.  An overview of these observations and other design considerations will also be provided.