2013 Gull River flooding report

Trent-Severn Waterway National Historic Site

This is a third party report and we are providing it for information only.

On April 18th, 2013, water levels started to rise. Then on April 19th, 2013, localized flooding and road washouts began to be reported to the Haliburton Sector Office of the Trent-Severn Waterway (TSW) National Historic Site of Canada. Warming weather and heavy rain resulted in the rapid melting of the existing snowpack and generated very significant inflows into the lakes and rivers within the Trent and Severn River basins. Some lakes increased by approximately 30 cm overnight.

The current study provides Parks Canada Agency (PCA) with a fact based review of flooding that occurred between the period of April 18th and May 15th, 2013 in the Gull River sub-watershed.

The analysis showed that heavy rainfalls in April combined with snowmelt were sufficient to generate large runoff volumes, and therefore large flood flows, resulting in a flood exceeding the 200 year flood in the Gull River:

  • On April 17th, Moore Lake Dam (Elliott Falls) and Gull Lake Dams, the two reservoirs immediately downstream of Minden Hills, were fully open (all stoplogs out).
  • On the evening of April 17th, when the heavy rainfall started, water levels and flows were within usual level range for most of the reservoir lakes, and started to increase on April 18th.

With all the stoplogs out at Moore Lake Dam and Gull Lake Dams, for any flow increase entering these lakes, water level had no other option than to increase. The only option that PCA had to avoid additional flooding in Minden Hills and downstream of Minden Hills was to retain water in the upstream reservoir lakes to decrease the flow entering Gull Lake.

Considering potential public safety issues to the permanent community of Minden Hills and downstream to Coboconk, the decision to put back stoplogs in the reservoir lakes upstream of Minden Hills to prevent greater downstream flooding was taken. On April 21st, addition of stoplogs occurred and continued the two following days.

In general, the management decisions contributed to reduce the peak flood flow on April 25th and therefore avoided additional flooding in Minden and downstream to Coboconk, without endangering public safety in upstream reservoir lakes.

The flood was not caused by poor decisions. The management staff at the Trent-Severn Waterway did an exemplary job. Other alternative water management decisions would not have led to a reduced overall flooding.

In summary, the flood event analysis showed that:

  • The management of the reservoir lakes did not contribute to the flooding near Minden Hills. Furthermore, the management succeeded in avoiding additional flooding on April 25th by retaining water in the upstream reservoir lakes.
  • The management in reservoir lakes was performed adequately within the recognized operational procedures in order to meet the prioritized water management objectives.

A review of legislation, policies, guidelines, emergency response plans and other texts was performed to identify the roles and responsibilities of PCA. In light of the review performed:

  • PCA is responsible for the management of water levels within the TSW.
  • PCA is responsible for the safe management of its structures and for ensuring the structures remain in compliance with regulations.
  • PCA has the responsibility to operate its dam-reservoirs to mitigate flood impacts.
    • Upstream flooding is an acceptable practice to prevent greater downstream impacts, especially if public safety is jeopardized.
    • PCA’s management of the April 2013 flood has not differed from its policies and operational procedures.

Recommendations

The management staff should eventually have a management tool to support decision making. This tool would help in better management for extreme weather events by the TSW.

It is also recommended that dam safety reviews continue to be carried out for all sites to analyse structural stability of all dams, to provide inundation mapping in case of a dam failure and to have emergency preparedness and response plans available to better assure public safety under large flood conditions.

To request a copy of the 2013 Gull River Flood Review please contact the Director's Office of the Trent-Severn Waterway. Thank you.

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