Minimizing Erosion Hazards in a Dynamic River System
The Lower Ausable River in Port Franks near Grand Bend, Ontario is a dynamic river system that poses a significant flooding, erosion and ice hazard to adjacent properties. The Armstrong West Subdivision is particularly prone to streambank erosion which has accelerated in recent years, averaging more than 5 m (16 ft) per year since 1999, primarily due to below-average levels in Lake Huron. 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 was further refined based on analysis using a two-dimensional hydraulic model, RMA-2. The final design featured seven bendway weirs on approximately 40 m (130 ft) centers, (typically 2.5 m (8 ft) high and ranging from 15-30 m (50-100 ft) in length with an orientation of 60–80 degrees clockwise from shore) and approximately 325 m (1,070 ft) of rock revetment along the shoreline. Construction was completed in November 2006 and featured over 12,900 metric tons (14,200 short tons) of rock material.
This chapter 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.
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