Wednesday, May 18, 2016

What will the Narramissic look like without the dam?


Aerial view of the Orland Village Dam and Narramissic River. Photo by J. Royte
Removal of the dam would restore tidal conditions in the Narramissic River. (The existing dams at Alamoosook Lake and Toddy Pond will remain in place as part of the current proposed project.) Projections of what the river would look like without the dam are based on historical documents, environmental assessments, and engineering studies.

Engineering assessments included borings, water quality studies, and mapping the river bed, to evaluate potential conditions after dam removal. The available information suggests that the river will be constantly in motion, fluctuating with the tide, as a lot of water moves back and forth twice a day. Restoration of tidal conditions will substantially increase flow in the Narramissic River, with daily tidal flows exceeding 500 cubic feet per second (compared to 20 cfs now).

Some sediment and rubble has accumulated between the dam and the Castine Road Bridge; this material would wash downstream, revealing the "Lower Falls"--an area of rapids and tidal or reversing falls. Similar tidal or reversing falls can be found in Damariscotta, Blue Hill, and the Bagaduce River. There is not a lot of sediment upstream from the Castine Road Bridge because the dam at the Upper Falls (Alamoosook Lake) prevents downstream sediment transport.

Downstream of these rapids, the river would look mostly the same, although water quality (dissolved oxygen levels, temperature, etc.) will likely improve with restored tidal exchange.

Above the rapids, the water level in the village area will change depending on the tide. At high tide, the area will look almost the same, with a drop of about one foot (very similar to when the dam gates are open).

At low tide, the water level will be five feet lower than present, leaving a channel with a depth of seven feet in the middle of the river between the Castine Road and US Route 1 bridges. It will still look like a river at low tide, with rapids at the dam site (accentuated by the constriction of the Castine Road Bridge) and more rapids upstream.

Vegetation along the sides of the channel will change from freshwater plants to salt water plants, with salt marsh possibly developing in the wetlands at Duck Cove and up Whites Brook (consultants noted that the shape of the brook channel looks like a tidal stream, and peat is present beneath the surface soil layer, indicating that there was originally salt marsh in these areas). Especially in the narrower reaches, conditions will be similar to those below the dam, where coarse substrate (cobble, boulder) will be watered and dewatered with the tides but without a lot of vegetation due to velocities. Large expanses of mudflats are not predicted.

Projection of water levels (elevation at high tide in light and dark blue and low tide in light blue) without the dam, from Stantec consultants.

The natural upper limit of the tide appears to be Upper Falls, two miles upstream from the Orland Village Dam.

Consultants with Stantec who have been studying the river over the last several years created the following simulated images of the river at high and low tide.

Looking upstream from Narramissic Drive, high tide (simulation by Stantec)

Looking upstream from Narramissic Drive, low tide (simulation by Stantec)

Looking west from Lower Falls Road, high tide (simulation by Stantec)

Looking west from Lower Falls Road, low tide (simulation by Stantec)
Looking upstream from dam site toward Castine Road Bridge, high tide (simulation by Stantec)

Looking upstream from dam site toward Castine Road Bridge, low tide (simulation by Stantec)