As published in The Erin Advocate
Town council has authorized an estimated $15,000 in engineering work to plan repairs to the Station Road dam in Hillsburgh, despite concerns about the high cost of the entire project.
The road over the earthen dam and causeway started to subside last fall, and was closed after damage and unstable ground was detected in an underground culvert, west of the main spillway.
Closure of the route, which is next to the fire hall, means that emergency vehicles must travel an additional 6 km around the block to serve residents on the west side of the ponds.
The Town had been requesting direction from the Ministry of Natural Resources (MNR) on how to proceed with repairs, but there was no reply for four weeks. After the fire department had a delay in reaching a resident suffering a heart attack, there was pressure from the Town and MPP Ted Arnott, and a response arrived on March 13.
The MNR assessment creates a problem for councillors, since any option other than restoring the functions of the dam to their recently existing state could constitute a change to the area environment and fish habitat. That might involve a long design and approval process that could leave the road closed for an extended time.
"We have to get on with it – let's get it fixed," said Councillor Barb Tocher.
Another problem is that the approval agencies have used "assumptions and unconfirmed information" to determine flood elevations, according to Road Superintendent Larry Van Wyck. This has resulted in a "High" hazard classification, referring to the consequences (not the probability) of a dam failure.
The MNR points out that, based on Credit Valley Conservation (CVC) floodline mapping, the minimum "Regulatory Flood" depth is more than half a metre higher than the existing road level, meaning that the dam would be inadequate even if restored to its normal condition. Van Wyck believes the mapping is inaccurate, but that the Town must do a survey of the pond to prove it.
"They have some old information that is incorrect, and it's not based on a topographic survey," he said. "They have no idea how much water is being held on the north side of the road [or] on the south side of the road. The elevations of the floodplain used in the correspondence we received is higher than the elevation of the floodplain for which they approved the design of the fire hall."
In the next few weeks the Town will assess the volume and capacity of the pond, which could lower the hazard rating. A detailed design will also be created for full replacement of the existing culvert.
At the council meeting, Mayor Lou Maieron speculated that rebuilding the culvert area could cost between $250,000 and $500,000. While supporting restoration of the road, he questions the need to rebuild the culvert at its present location. Still, he voted with all other councillors in favour of the engineering work.
"I want to get it fixed, but I don't really want to go to all this trouble and expense for a pipe that doesn't serve the road," he said after the meeting. "If it doesn't serve the taxpayer, if there's no purpose for it, why have it go under the road?"
The culvert is considered part of the hydraulic function of the whole dam, increasing safety by adding an extra passageway for water, and the MNR requires that this function be maintained. Maieron raised the possibility of rebuilding the culvert away from the causeway, but was told this would take too long.
The quicker and less expensive possibility of repairing the existing culvert with an insert and grout would not be approved by the MNR. In his report to council, Van Wyck said that option "will not be acceptable as there is not sufficient bearing strength in the soil" according to current dam standards.
The water level in the pond has been lowered to reduce pressure on the dam by removing some boards in the control structure. If they stay out, it would increase the dam's ability to resist a flood peak and could reduce the hazard rating.
Van Wyck told council that if the pond level is lowered by removal of all the boards in the control structure, which would require removal of the sediment behind them, the MNR might not permit re-installation of the boards.
Marcy Quayle, who owns the land on the north (upper) side of the dam, does not want to see the pond drained.
"I am not interested in the removal of the dam structure, this includes the spillway under the bridge and the raceway. Now or in the near future. Nor am I bearing any costs that this may bring as the land owner," she said in a letter to Van Wyck.
John Kinkead, Director of Water Resources Management & Restoration for CVC said in a letter to the mayor that although CVC has no budget for helping remove the dam, that could be the best option.
"We all understand that the most fundamental requirement in moving forward is to ensure public safety," he said. "In light of the apparent cost and technical uncertainties around addressing hazard considerations should the dam remain in place, the preferred solution might in fact be the appropriate 'decommissioning' of the dam."
A 2002 fisheries plan authored by the CVC and the MNR identified the Hillsburgh dams as potential targets for "mitigation or removal" to benefit overall fisheries health. Dams block fish movement and result in higher water temperatures due to the ponds.
In a letter to council, Ron Moore, who recently moved to the area, said draining the pond would be a "detriment to the wildlife that inhabit the pond and the wetlands surrounding it" and that higher property taxes could be justified to preserve it.
"No one likes to pay more taxes, but I believe many in the area, not just those whose property backs onto the pond, would support keeping the pond as it is," he said.
