FLOW REGIME IN A NORTHEASTERN RIVER NETWORK INFLUENCED BY CLIMATE, HUMAN GENERATED DISTURBANCES, AND CIVIL INFRASTRUCTURE

The East Branch of the Penobscot River watershed in Maine has a history of deglaciation well over twelve thousand years ago and extensive deforestation and damming since European colonization of the landscape in the past three centuries. The glacial history and changes from human activities and civil infrastructure influence the modern flow regime and aquatic habitat in the mainstem Penobscot River. The history of mechanical processes related to ice, precipitation, landscape disturbances, and flow control structures presents challenges when attempting to distinguish the influence of human generated disturbances from climate forcing on the flow regime in the river mainstem. Alterations have included a substantial canal project in the mid-1800s that diverted outflow from an area of over several hundred square kilometers draining toward the St. John River into the East Branch of drainage network of the Penobscot River to deliver logs to Bangor, Maine. Accordingly, the modern river flow regime is governed by background watershed processes of precipitation delivery, vegetation interception and soil infiltration, logging operations, and the operation of dams at the outlets of two large lake complexes. Concerns with the effects from flow regime modifications to salmon habitat have inspired a recent study of watershed runoff and the river flow regime. Here we report on an investigation of flow regime conditions, changes, and predictions in the East Branch Penobscot River system. Long-term discharge time series from three USGS gage stations have been assembled to evaluate flow regime conditions over the past century. Historical records, engineering design plans, spatial data, and precipitation and temperature time series have provided a basis to create flow simulations under varied scenarios of watershed land cover, climate conditions, and dam management using the US Army Corps of Engineers HEC-HMS hydrologic model platform. Outcomes of our analyses are being framed to support for watershed management decision-making, including land uses and dam operations, with implications to Atlantic salmon habitat in Maine.