December 22, 2010

Expensive upgrades could reduce impact of dams

As published in The Erin Advocate

When I think of dams, I think of farms. They do not look much alike, but they are both drastic human interventions in the environment, redirecting the power of nature to serve our needs. Dams and their mill ponds are often quite scenic, but unlike farms, they have become industrial relics.

There are more than 500 dams in the Credit River watershed, including several in the Erin-Hillsburgh area. Most were built in the mid-1800s as European settlers made a furious effort to tame the Ontario wilderness, building mills to saw up trees as they cleared the land and grinding grain from the new farms.

Many dams are still worth preserving, for historical, cultural and environmental reasons. But are we willing to pay millions of dollars in the long term to maintain and rebuild structures that have lost their original economic purpose? Will our descendants see the value in them 100 or 200 years from now?

The best options for Erin dams will have to be determined by dam owners, the local community and technical studies. What follows is simply a look at what changes may be possible to improve safety and water quality.

With the provincial government considering expensive new regulations for maintaining dams, I called Bob Morris, an aquatic biologist and Manager of Natural Heritage at Credit Valley Conservation (CVC), to get some background.

CVC has no direct authority over normal dam operations. The Ministry of Natural Resources (MNR) is responsible for dams, but does not currently keep track of their maintenance. The CVC and MNR get involved when permits are needed for repairs or alterations. Dam owners are liable when a dam fails and causes damage to other landowners downstream or to the river environment.

"It is assumed that dam owners would take necessary precautions to prevent such an event but regulations are not likely to be applied until such a failure," said Morris.

"Dam owners must apply for a permit to repair or alter a dam and only then does MNR become aware of any safety issues. It would be unlawful to flush sediments downstream. Owners are responsible for maintenance, operations and surveillance of their dams."

The Charles Street and Church Street dams in Erin village were identified in 1997 as "structurally inadequate" by modern standards, but the CVC would not offer an opinion on their current safety or need for repair. The Church Street structure has some areas of crumbling concrete, but to an amateur observer it appears to be solid.

CVC can provide maintenance advice to dam owners to reduce damage to the environment and improve safety. Possible changes include fish ladders or rocky ramps, designed to enable migration of local fish species.

Ponds typically have higher water temperatures, which can be detrimental to the environment downstream. This can be offset by a "bottom draw", a separate pipe which in the summer would discharge some of the cooler water at the bottom of a deep pond.

Other pond problems include sediment build-up, high levels of nutrients and low levels of dissolved oxygen, leading to algae growth. Dredging and disposing of sediment is very expensive, and does not provide a long-term solution.

"CVC promotes the development of wetland communities in impoundments to improve some water quality parameters and habitat values," said Morris. "Dredging is generally discouraged."

Other possible changes include lowering a dam, which would leave the sediment in place and result in more wetland vegetation. Bypass channels can be used to divert a portion of the river flow around a dam, or even around a whole pond. Rocks can be used to build up the stream bed near a dam, or create a stepped series of riffles and pools.

If it is determined that a dam should be removed, the largest environmental concern is to avoid releasing sediment downstream during the project.

"Full removal of the dam and sediment would achieve full stream and valley restoration, that is best in many situations, but not always feasible in terms of economics and landowner objectives," said Morris. "The main issue seems to be public acceptance of losing a cultural feature and open water body that is different from a stream. Cost is also a big issue – but so are repairs or liability costs after a failure."

Could our dams be part of a plan to bring more tourists to the area? Are they essential for stormwater management? More on these issues next week.