September 10, 2010 - Cobbossee dam repairs

Dam repairs pose interesting technical, environmental, and social challenges.  The situation with the Cobbossee Outlet Dam, in the town of Manchester, Maine, provides a good example.

For your reference, here is a Google map of the dam site.  This is several miles farther upstream from the New Mills Dam in Gardiner, which had its own dam repair and drawdown issues this spring.

The Town of Manchester owns the dam, which maintains the water levels in 5,000-acre Cobbossee Lake above, as well as ensuring adequate flows in Cobbossee Stream below the dam.  In all, parts of six municipalities are affected by the waters of Cobbossee.  The dam is damaged: one of its six gates is currently boarded up because it was at risk of failing.  Rotting wooden timbers need to be replaced, possibly with galvanized steel beams.

To perform the repairs, the lake level may have to be drawn down.  This concerns boaters on the lake, who fear that the drawdown might end the boating season early.  To address this concern, the plan is to do the dam repairs during this fall's annual seasonal drawdown of the lake.  Many dam managers perform drawdowns in the fall for flood control and to make room for spring runoff. 

Cost and cost-sharing are also at issue.  Currently, as the dam owner, Manchester appears to be on the hook for the repair costs, although there is talk of asking other communities along the watershed to pay into a repair fund.  It will be interesting to see how the project progresses.