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| 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 Projections of what the river would look like without the dam are based on historical documents, environmental assessments, and engineering studies.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.
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| 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.
