3.2 Water Quantity
- Drainage is conveyed through the subwatershed
through several streams and channels to Long Lake,
which outlets through Long Lake Creek.
The Upper Watershed Stream
Assessment identified 16 erosion locations on the creek, most of them
concentrated in about 1,000 linear feet of that study’s Reach 5. The
HHPLS included a study of scour potential in the creek, and concluded that
some reaches were at moderate to high risk for erosion.
- The HHPLS identified a number of
locations that are predicted to overtop during the 100 year event, including
park trails within the Wolsfeld Woods SNA; two private drives; a private
field road; a portion of East
Long Lake Road; and along Fox Street in Orono. The Regional Team participating in the
HHPLS process confirmed occasional flooding of East Long Lake Road. In addition, the HHPLS model predicts
other locations in the subwatershed that would not overtop but which may
have a minimal amount of freeboard above the 100-year flood level. More detail is available in the HHPLS. Local governments should review these
observed or potential locations and assess whether the risk of occasional
flooding is acceptable or should be addressed.
- Development, redevelopment, and
reconstruction in the subwatershed, especially in the area west of Long
Lake and north of US Highway 12, is predicted to increase volume of
stormwater runoff from the watershed as well as increased nutrient and TSS
loads. The HHPLS model predicted
that development in the western subwatershed along the US Highway 12
corridor by 2020 would likely have impacts on the ravine carrying drainage
from that area to the Park Ponds and thence to Long Lake. The HHPLS scour analysis identified that
reach as having high erosion potential, and the Regional Team identified
an erosion site on that channel.
- The HHPLS identified several locations
where, for both existing and future conditions, higher velocities than
desired may result in erosion at outlets or culverts. These
include private drives, four city streets, US Highway 12 crossing, and a
Luce Line Trail crossing. Erosion
control or energy dissipation measures may be required in those locations.
- Several landlocked basins are present in the
subwatershed. Outletting will
generally be discouraged unless there is a demonstrated threat to property
structures or public safety. Mooney Lake
has no natural outlet, and stormwater volume from upstream development in Plymouth results in
periodic flooding. The District has
developed and implemented a cooperative emergency pump-out plan with the
City of Plymouth, but a long-term solution
of volume reduction in Plymouth
and a more permanent emergency outflow pumping solution is needed.