The Impacts of Dam-Related Flow Regulation on the Physical and Ecological Characteristics of Rivers

Dartmouth College, Hanover NH

Investigators

Abstract

Dams generate significant hydrogeomorphic alterations that have profoundly altered and degraded river ecosystems. General agreement exists within the aquatic community that particular nodes or zones within the riparian environment reflect and record disturbance in important ways and become critical bio-indicators of ecological integrity. These aquatic hotspots commonly occur where hydrologic flow paths converge with some fundamental ecological and geochemical component, such as at tributary junctions. Numerous previous studies have chronicled the hydrologic, geomorphic, or ecological impacts of dams, but rarely have these three responses been simultaneously evaluated in a watershed perspective where multiple dams exist. Few comprehensive evaluations exist of the hydrogeomorphic effects of dams that both examine whole watersheds and that encompass an array of dam types and operation strategies. The main goals of this research project are to elevate the analysis of dams away from a primarily singular case study view and to specifically link the ecological impacts of dams to the geomorphic response resulting from these hydrologic changes. Dams fragment watersheds, and the normal spatial suite of geochemical, ecological, and geomorphic processes are greatly disturbed along mainstems and at tributary junctions with the mainstem. This project will evaluate sediment sources and residence times at the event-to-decadal timescale in systems disturbed by multiple dams. The project also will determine the length-scale and magnitude of this disturbance on aquatic ecosystems at the watershed scale. Another main objective of the project is to evaluate how different dam types and management styles generate different sediment fluxes and resulting aquatic ecology. The residence time of this sediment embedded in the channel bed will be documented using short-lived radionuclides, such as 210-Pb and 7-Be. The project focuses directly on the effects of dams on both sediment storage and the residence time of bed sediment and their distinct or combined control on benthic community structure. This research will be conducted on tributaries and mainstem sections of the Upper Connecticut River watershed, a basin with a history of extensive damming and where extensive base data exist. This research has several important scientific and social components. Scientifically, the use of fallout radionuclides has far-reaching implications. There is no known quantitative expression of embeddedness, and these results could establish this technique as the scientific standard not only for studies related to dams but also for fisheries management in general. This research also is expected to have significant benefits for society, as its results will be important for Federal Energy Regulatory Commission (FERC) relicensing and for National Environmental Policy Act (NEPA) compliance. The research results also will help establish the necessary base conditions for adaptive management strategies.