Thames River Watershed Barriers Assessment Project

Dams and other structures such as road and train crossings, culverts, and weirs create barriers or impoundments on watercourses. Many dams and reservoirs are highly valued by their local communities for their recreational and aesthetic uses as well as their historical significance. Other structures are important for their role in flood control or flow augmentation.

However, dams and other barriers can also have major negative impacts on aquatic ecosystems. The adverse effects include barring migration of fish and wildlife, increasing soil deposition and erosion, altered water quantity and quality, eutrophication (excess nutrients that cause excessive algae growth and a resulting lack of oxygen), and wildlife mortality.

The Canada-Ontario Agreement Respecting the Great Lakes Basin (COA) and the Lake Erie COA partners (Lake Erie Management Unit, Aylmer and Guelph District MNR offices) provided funding to assess the 225 barriers found throughout the Thames River watershed. The purpose of the Thames River Watershed Barriers Assessment is to assess the impacts of impoundments, prioritise them for removal or mitigation, and develop a plan of action for those impoundments identified as priorities. The criteria developed to rank the impoundments for their removal or mitigation consider their current function, age, structural integrity, and impacts on the aquatic ecosystem.

Dingman Creek Weir Removal

When the criteria were applied to the list of barriers, the Dingman Creek Weir (pictured at right), located in southwest London, was identified as a top priority for removal or mitigation. Since this barrier was the first to proceed beyond the criteria towards action of removal or mitigation, it was considered a pilot project. Progress was tracked and documented in order to prepare a guide for removing or mitigating barriers.

At over 50 years old, the Dingman Creek Weir was deteriorating and no longer served its original purpose.

The weir, which was owned by the City of London, was a concern in terms of both its impacts on the health of Dingman Creek and public safety. Removal of the weir structure was also one of the recommendations from the recently completed Dingman Creek Subwatershed Study Update.

The City, with participation from the UTRCA, studied remedial options for the structure through the Municipal Class Environmental Assessment process. The study evaluated the effects of various options for the Dingman Creek Weir, ranging from doing nothing to completely removing the structure.

The preferred option, based on the study as well as public and agency input, was to completely remove the weir and restore the aquatic habitat. As a result, the Dingman Creek Weir was removed in September 2005 (bottom photo). Heavy equipment was used to remove the weir and to restore aquatic habitat using natural river stone. COA and the Lake Erie COA partners also provided funding for the removal of the Weir.