A recent study found seepage and significant deterioration at the Little Hope dam in the town of Dayton.
It is located directly across County Road K from the Old Red Mill – a mill that dates back to the 19th Century when it powered a gristmill.
The dam consists of an earthen embankment leading to a stone and concrete spillway with three stop log bays and another earthen embankment.
The dam creates a millpond of nearly 25 acres along the Crystal River. More than 20 homes are located around the millpond.
Engineers with the Eau Claire office of Ayres Associates surveyed the dam in January and presented their study of the Little Hope dam to the Waupaca County Parks and Recreation Committee Thursday, Sept. 8.
The study concluded that the current dam needs to be replaced or repaired. It recommended against doing nothing.
“If a rapid catastrophic failure of the dam were to occur, it would result in a rapid release from the lake with a wall of water impacting County Trunk Highway K downstream of the structure. This could cause County K to wash out and result in a significant risk to the general public, as well as the cost to the existing structure,” the report said.
Ayres Associates provided cost estimates for four options, ranging from removing the dam for about $210,000 to replacing it with an armored overflow section and new stop log bays for a cost of $425,000.
Removing the dam would allow the stream to revert to its natural condition. However, the Ayres study indicated that a 600-foot long, 30-foot wide and 3-foot deep channel would have to be dredged upstream of the dam site.
Another option would be to replace the stop log structure with two split leaf gates for a cost of $405,000. A third option is to replace the current dam with a labyrinth spillway, which would also cost about $405,000.
Dayton Town Chairman Chris Klein is concerned that the county could choose the least expensive alternative of removing the dam.
“Water levels would drop by up to 7 feet, dewatering the millpond and the adjacent wetlands,” Klein said in a letter to area residents. “Current owners adjacent to the millpond would probably become owners to the middle of the new streambed; likely having more acreage; but likely having lower property values.”
He described the additional land that adjacent property owners would gain from draining the millpond as “a mixture of river silt and bottom muck. This land generally cannot be maintained as regular residential property.”
Klein has recommended that property owners along the millpond form an independent lake district.
“A lake district would both be able to raise funds by a tax levy or by applying for grants from the DNR or other agencies. Goals of the lake district could include improving water quality of the millpond by removing silt or weeds, working with the county on maintaining the dam, improving the recreational use of the millpond or improving the quality of life of the area,” Klein said. “This option is not available if the Waupaca County Board removes the dam.”
One issue raised by the study is that Little Hope dam may be incorrectly classified as a small dam.
Small dams have to meet less stringent regulatory requirements than large dams, which are defined as having more than 50-acre feet of storage and over 6 feet of hydraulic head.
According to records of the state Department of Natural Resources, Little Hope dam has a hydraulic head of 7 feet and a maximum storage of 40-acre feet. However, based on a 2005 aerial photo, the dam’s impoundment is nearly 25 acres and would need to have an average depth of only 2 feet in order to be under 50-acre feet of storage.
As a consequence of the study, the county now needs to have the DNR confirm the dam’s classification, which may in turn affect what options are open to the county.
Roger Holman, director of the Waupaca County Parks and Recreation Department, said the county requested the study late last year after noticing scouring and concrete breaking away on the dam.
“We realized that the level of maintenance may exceed what we were capable of doing,” Holman said. “We decided to have a study done so we could look at our options.”
Holman said the county has made no decision yet regarding the dam.
“Based on the engineer’s study, we don’t feel we can maintain the current structure,” Holman said.
He said the county will not have funds available in next year’s budget for the dam, indicating that it may be two to three years before the county does any work on the project.
In addition to reviewing the dam’s classification, Holman said the county would ask the DNR to examine the dam’s impact on water quality.
The study did not offer any predictions regarding the dam’s future viability.
“It is not possible to predict the remaining life of a structure, especially a dam that is subject to unpredictable flood conditions,” the study noted. “A significant flood event could wash the structure out tomorrow or it could remain for 10 to 15 years with little maintenance.”