Wetland Assessment & Mitigation
T6 R13 Piscataquis County, Maine
When Great Northern Paper, Inc. (GNP) renewed federal licenses for the
Penobscot Mills and Ripogenus Hydroelectric Projects located in the upper
Penobscot River basin in north-central Maine, FERC required that GNP implement
measures to enhance approximately 280 acres of shoreline wetlands within the
project impoundments.
Develop a final wetland enhancement plan, which included a feasibility
assessment of the enhancement measures stipulated by the license articles,
evaluation of alternative measures, working with GNP and a team of natural
resource agency representatives to select the preferred site(s), and preparation
of text and drawings for the final wetland enhancement plan. Following FERC’s
approval of the final wetland enhancement plan, Devine Tarbell & Associates,
Inc.’s (DTA) staff was retained by GNP to monitor the recovery and development
of wetlands as required under the articles of the license.
Umbazooksus Lake, a 1,600-acre storage impoundment located immediately upstream
of Ripogenus impoundment, was selected by the interagency team as the preferred
site. DTA’s staff, working with GNP biologists, concluded that as much as 600
acres of wetland could be restored and enhanced at Umbazooksus Lake simply by
maintaining the outlet gate in a permanently open position.
Selection of the Umbazooksus Lake alternative over the measures that were
originally stipulated in the license articles resulted in twice the required
enhancement area at an estimated savings of nearly $4 million for GNP.
Opening the gate at the outlet of Umbazooksus Lake will lower overall water
levels and reduce annual water level fluctuations in the impoundment. Future
water levels will be driven solely by seasonal variations in runoff and
precipitation. Once exposed, most of the former fluctuation zone will regenerate
as forested and shrub-dominated wetlands supported by groundwater seepage. In
addition, emergent and floating-leaved wetlands will develop in shallows that
were formerly too deep to support wetland vegetation. Recovery and development
of wetlands along Umbazooksus Lake will be monitored by comparing extent, cover
types, and plant diversity at two-year intervals along a series of permanently
established transects.
For the required monitoring, DTA’s staff will use bathymetric and wetland maps
prepared during the development of the enhancement plan. Using a Trimble Pro-XR
GPS unit combined with a DST-50 transducer remote sensor and depth measuring
equipment, DTA’s staff were able to accurately map the lake bottom in a fraction
of the time required using conventional methods.