Anthropocene streams and base-level controls from historic dams in the unglaciated mid-Atlantic region, USA

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
By: , and 

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Abstract

Recently, widespread valley-bottom damming for water power was identified as a primary control on valley sedimentation in the mid-Atlantic US during the late seventeenth to early twentieth century. The timing of damming coincided with that of accelerated upland erosion during post-European settlement land-use change. In this paper, we examine the impact of local drops in base level on incision into historic reservoir sediment as thousands of ageing dams breach. Analysis of lidar and field data indicates that historic milldam building led to local base-level rises of 2-5 m (typical milldam height) and reduced valley slopes by half. Subsequent base-level fall with dam breaching led to an approximate doubling in slope, a significant base-level forcing. Case studies in forested, rural as well as agricultural and urban areas demonstrate that a breached dam can lead to stream incision, bank erosion and increased loads of suspended sediment, even with no change in land use. After dam breaching, key predictors of stream bank erosion include number of years since dam breach, proximity to a dam and dam height. One implication of this work is that conceptual models linking channel condition and sediment yield exclusively with modern upland land use are incomplete for valleys impacted by milldams. With no equivalent in the Holocene or late Pleistocene sedimentary record, modern incised stream-channel forms in the mid-Atlantic region represent a transient response to both base-level forcing and major changes in land use beginning centuries ago. Similar channel forms might also exist in other locales where historic milling was prevalent.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Anthropocene streams and base-level controls from historic dams in the unglaciated mid-Atlantic region, USA
Series title Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
Volume 369
Issue 1938
Year Published 2011
Language English
Publisher Royal Society Publishing
Publisher location London, UK
Contributing office(s) Maryland Water Science Center
Description 34 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
First page 976
Last page 1009
Country United States