HUMANS, DAMS, AND FLOW REGIMES IN THE PENOBSCOT RIVER

The Penobscot River watershed was altered by humans throughout the colonial and industrial time periods, resulting in a variety of effects on surface hydrology. Long term river discharge measurement records provide a basis for the quantification of the changes to the Penobscot River system following the construction and operation of major dams; however, the records do not extend back to the period before large dams were in place. Discharge records from other regions have been used to characterize changes in flow regime following upstream dam construction, revealing that dammed flow rates are less variable, baseflow discharges are higher, and relatively high peak runoff rates from precipitation events are smaller in magnitude. Interests in restoring aquatic habitat conditions in the Penobscot River has inspired an examination of cumulative flow regime changes resulting from dams over the past century. This study focuses on the regime changes using discharge measurement time series from USGS gage stations and simulated discharge time series derived from a watershed-scale hydrologic model (HEC-HMS). Flow regimes are characterized using measurements when available before and after major alterations. Simulations are used to represent the watershed without dams or the Chamberlain Lake diversion into the East Branch of the river network. Results from analyses of flow regimes relative to the placement and operation of dams will be presented with discussion of watershed management implications. The research approach provides a basis for quantifying the cumulative effects of flow regulation by dams and diversions in relatively rural forested settings to support decisions related to tradeoffs between dams, industrial activities, and aquatic habitat management in the Northeast.