3.2 Water Quantity

  1. 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. 
  2. 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.
  3. 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.
  4. 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.
  5. 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.