What is the risk if a dam fails in Manchester?
Ford Dam at Village Hall, 912 City Road
On May 19th, the whole country watched on national news as the Edenville Dam outside of Midland failed, and caused the failure of the Sanford Dam, the evacuation of 10,000 residents, extensive flooding throughout eastern Midland and low-lying parts of its downtown district, and severe damage of most of the Village of Sanford. It also led many to wonder what risk does Manchester face if one of our dams fails.
The Edenville Dam had a “high” hazard rating from the Michigan Department of Environment, Great Lakes and Energy (EGLE). There are eight dams in the Manchester area regulated by the State of Michigan. Of the eight, two are also rated “high” for downstream hazard potential. They are the two dams in the Village of Manchester.
Hazard potential rating is not based upon the structural or hydraulic condition of the dam. The State of Michigan defines “High hazard potential dam” as “a dam located in an area where a failure may cause serious damage to inhabited homes, agricultural buildings, campgrounds, recreational facilities, industrial or commercial buildings, public utilities, main highways, or class I carrier railroads, or where environmental degradation would be significant, or where danger to individuals exists with the potential for loss of life.”
The larger of the two potentially hazardous dams is the Manchester Ford Dam, owned by the Village and located next to Village Hall and the Manchester District Library. It was built in 1940.
Is Manchester looking at mass evacuations and houses washed off foundations if the Ford Dam fails? No. While damage to structures is possible and under very specific conditions, there may be danger to life were the Ford Dam to fail, the scale of the potential hazard is magnitudes different. Wixom Lake, the body of water formed behind the Edenville Dam, covered 1,980 acres. In contrast, the pond formed behind the Ford Dam covers 45 acres.
Emergency Action Plans are required for all dams which have a “high” or “significant” hazard potential rating. Village manager Jeff Wallace explained that the Village’s Emergency Action Plan for Ford Dam, updated every couple of years, is assembled and ready to be grabbed if something should happen to the Ford Dam. He stated that besides the state, the plan is also shared with the waste water treatment plant, Washtenaw County Sheriff’s Office, Manchester Township Fire Department, Washtenaw County Operation Center director & dispatch, and the owner of the next dam downstream. The Village most recently updated its Emergency Action Plan in June 2019.
How much property is in danger from a catastrophic failure of the Ford Dam? Determined by an engineer, using many hypothetical situations and mapping up to five miles downstream, five parcels are at risk. Wallace clarified, “Not that the property would be destroyed, but affected … it would fill floodplains, but would not wash away homes.” Wallace also pointed out that the first property that would be affected is the Water Treatment plant, owned by the Village and while it would get a fair amount of water flowing through it, the water would recede quickly.
Every three years the dam needs to be inspected. While the option exists to hire a private contractor to inspect the dam, the Village opts to hire the State of Michigan to do the inspection. The State gives a more objective look, Wallace explained. The dam received a “fair” structural rating during its most recent inspection in December of 2019. Additionally, the inspection report always includes maintenance the Village needs to do on the dam, including cutting brush and trees.
This time around the Village does have additional work in front of them to maintain the dam. The inspection report is requiring the Village to get one of the two drawdown gates operational and to hire an engineering firm to check the dam’s engineering within the next four years. This engineering evaluation will be the first one done since the Village purchased the dam 20 years ago, and is more involved than the routine inspections. This evaluation will involve a diver inspecting the underwater portions of the dam and taking underwater photos.
Read more about the most recent inspection here: Village’s Ford Dam still in “fair” condition, says EGLE
When asked if the village was doing anything different in light of the Edenville Dam failure, Wallace stated that the village had already budgeted $20,000 in February to hire the engineer firm to do the evaluation. “It is the right thing to do, so you do it,” he stated.
The evaluation is the start of a process that could take years. Depending on what the evaluation shows, there could be difficult decisions down the road. For example, the village may have to choose between expensive repairs versus removing the dam. Wallace reassured that if it comes to that, many things would have to be taken into account, and the public would be a big part of that decision.
Hydro-electric dams are also regulated by the Federal Energy Regulatory Commission. While the Ford Dam used to be a hydro-electric dam, the equipment to make electricity is no longer in the basement of the Village building. The Village investigated generating electricity with the dam when they purchased the building, but discovered it would not be cost effective, would require an engineer to operate, and would be very loud.
Manchester Mill Dam in downtown Manchester
The other “high” hazard dam in Manchester is the Manchester Mill Dam, owned by Alwicz Holdings. It is the dam the Main Street Bridge runs over and was built around 1908. While the Ford Dam pond is 45 acres, the Manchester Mill pond is 12 acres.
The owners of the Mill Dam were contacted for this article but declined to answer questions.
While we don’t know for sure what the property damage would look like if the Mill Dam failed, we do know that it would not include the Main Street Bridge. The former bridge was anchored to the dam, but the Village had the new bridge engineered independent of the dam so it would be unaffected if the dam were to fail catastrophically or be removed in the future. The Manchester Mill Dam received a “fair” structural rating during its last inspection in 2016.
The remaining dams regulated by the State in the Manchester area include Sharon Mills Dam, Wilo’s Lake Dam, Broucek Dam, Clark Dam, Iron Lake Dam, and Baker Dam. According to the Michigan Department of Environment, Great Lakes and Energy, these are all rated as “low” hazard and all received “satisfactory,” “fair,” or “not rated” condition ratings at their last inspections.
Dams regulated by the State of Michigan shown in blue and purple. The other dam in the Manchester area not shown here is Baker Dam located north of Grass Lake Road in Sharon Township.
The only dams near us, in either the River Raisin or Huron River watersheds that are “significant” or “high” hazard risk AND rated “poor” are in Tecumseh, which is downstream from the Manchester area and would not impact our area if they fail.
Like the two dams in the Village of Manchester, Edenville Dam also was given a “fair condition” rating after their most recent inspection in 2018, but structural condition only tells half the story. The Edenville Dam was not designed to handle large floods. Since 2004, the Federal Energy Regulatory Commission ordered the dam owners to build two additional spillways to accommodate additional flooding, and for the next 13 years, the owners missed deadlines to add the spillways and produced only excuses.
Unlike the Edenville Dam owners, the Village is on schedule with Ford Dam maintenance. Wallace stated, “We follow the rules.”
Another view of Ford Dam
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