2 The Legacy of Humans and Glaciation in Northeastern Rivers

Sunday, 18 March 2012
8:00 AM - 12:00 PM
Capital Room 1

PRE-DAM REMOVAL GEOMORPHIC MONITORING ON THE PENOBSCOT RIVER, MAINE

Paper number: 2-12
Program: Theme Sessions
Time: 11:40 AM – 12:00 PM

Authors

Abstract

Dams are one legacy of human involvement with rivers. Built to harness energy for logging, mills, hydroelectric power generation, and other human uses, dams have changed the geomorphic and biologic characteristics of watersheds across the nation. As the environmental consequences of these structures are recognized, dam removal is seen as a way to restore lost habitats and rebuild ecological communities. Currently, the largest of these projects on the North American East Coast is being undertaken in Maine. The Penobscot River Restoration Project plans to remove two of the lowermost dams on the Penobscot River, Maine’s largest river, and to build a fish by-pass around a dam on a principal tributary, in an effort to restore 11 species of sea-run fish while maintaining energy production. The removal of the first dam is scheduled for 2012.

Geomorphic monitoring was undertaken at monumented river cross-sections within areas anticipated to be affected by the dam removals to provide baseline data on pre-dam removal channel bathymetry, sediment size, and bank conditions. Data collection included repeated, seasonal photographic surveys, bathymetric surveys at each cross section, video-based channel sediment characterization, bank geomorphology studies, and geophysical characterization of impoundment sediment thickness. Post-dam removal monitoring at these locations is planned. Over the two-year monitoring period, few changes were noted in river bathymetry or bank characteristics. Channel sediment characterization revealed that, within the study area, the Penobscot River channel in both flowing and impounded reaches is dominated by coarse sediment, ranging from gravel to boulder-sized clasts with a predominately sand matrix. This contrasts with the fine-grained sediment storage found in many impoundments, and is interpreted to be an artifact of the region’s complex Late-Pleistocene and Holocene geological history and the dams’ physical features and modes of operation.