Coping with Mother Nature – minimizing flooding, erosion and ice hazards in a dynamic river system

The Lower Ausable River near Grand Bend, Ontario is a dynamic river system that poses a significant flooding, erosion and ice hazard to adjacent properties. In the Armstrong West Subdivision, streambank erosion has averaged more than 5m per year since 1999. Several properties have been permanently submerged and other properties and structures are currently at risk due to the natural river migration and erosive action of flood flows and ice floes on the sandy streambanks. In order to protect properties from these hazards, a series of “bendway” weirs was designed to redirect flow away from the shoreline and re-establish the bank by inducing sedimentation behind the weirs.

The conceptual design of the erosion control works was developed based on model results using HEC-RAS and further refined based on analysis by others using a two-dimensional hydraulic model, RMA-2. The final design featured 7 bendway weirs on approximately 40m centers, (typically 2.5m high and ranging from 15-30m in length with an orientation of 60–80 degrees clockwise from shore) and approximately 325m of rock revetment along the shoreline. Construction was completed in November 2006 and featured 13,000 metric tons of rock material.

This paper highlights the key project features and discusses the critical lessons learned from all phases of the project including planning, design, permitting, construction, and post-construction monitoring.