Penobscot River Processes, Aquatic Habitat, and Management
The Penobscot River is the mightiest of Maine’s coastal rivers, with a watershed covering ~8,600 square miles (22,274 square kilometers) of land across seven Maine counties and stretching from its mouth near Bucksport in Penobscot Bay to the drainage divide in the Boundary Ranges of the Appalachian Mountains at the state’s western border with Quebec. The Penobscot watershed is the homeland of the Penobscot Nation and the river is integral to cultural and traditional practices.
Over the past two centuries, the construction of large channel-spanning hydropower dams has changed the water flow regime in the river, prevented navigation, and closed thousands of miles of habitat for sea-run (diadromous) fish. In recent years this trend of dam construction was reversed with multiple dams being removed to return the lower Penobscot to free-flowing conditions.
WPES members have been involved in research surrounding the ways the river has responded to the changes related to land uses, dam construction and maintenance, and climate.
Penobscot Geomorphology
Landscape Scale
Long-term geological processes create structures that have a substantial influence on the modern form, position, and profile of the river system. The geologic materials also are the parent material for soils in the watershed and that supply sediment of varied grain sizes to the river.
Regional Geology – Geologic history of the Penobscot River basin.
Watershed Scale
The dimensions of the Penobscot River watershed are predominantly governed by landscape-scale processes related to long-term tectonics, geology, and glaciation in the region. Humans have also influenced the modern dimensions of the watershed through flow diversions at the upper most ends of the basin.
Reach Scale
Plan view of the Penobscot River at Ayers Island in Orono, showing locations of valley cross sections used in a hydraulic model.
Surface water from precipitation and groundwater flows moving through the Penobscot River watershed travels from hillslopes into streams a person can jump over to large rivers you need a boat to cross. The streams and rivers comprise the watershed drainage network made up of links having unique characteristics governed by the geology, climate, watershed characteristics and position, and disturbances from human activities. Segments within the river mainstem and tributary streams are referred to as “reaches”, which can have unique characteristics relative to upstream and downstream locations in a drainage network.
Feature Scale
Man made features called “boom islands” from historic log drives on the Penobscot River. Learn more about how remnant boom islands can influence modern flow dynamics here.
Each reach of the Penobscot River drainage network is characterized by a collection of features related to structures, channel form, bottom substrates, and hydraulic conditions. The features influence flow dynamics, ecological conditions, and aquatic habitat important to many fish species.