Geomorphic responses to dam removal in the United States – a two-decade perspective

By: , and 
Edited by: Daizo Tsutsumi and Jonathan B. Laronne

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Abstract

Recent decades have seen a marked increase in the number of dams removed in the United States. Investigations following a number of removals are beginning to inform how, and how fast, rivers and their ecosystems respond to released sediment. Though only a few tens of studies detail physical responses to removals, common findings have begun to emerge. They include: (1) Rivers are resilient and respond quickly to dam removals, especially when removals are sudden rather than prolonged. Rivers can swiftly evacuate large fractions of reservoir sediment (≥50% within one year), especially when sediment is coarse grained (sand and gravel). The channel downstream typically takes months to years—not decades—to achieve a degree of stability within its range of natural variability. (2) Modest streamflows (<2-year return interval flows) can erode and transport large amounts of reservoir sediment. Greater streamflows commonly are needed to access remnant reservoir sediment and transport it downstream. (3) Dam height, sediment volume, and sediment caliber strongly influence downstream response to dam removal. Removals of large dams (≥10 m tall) have had longer-lasting and more widespread downstream effects than more common removals of small dams. (4) Downstream valley morphology and position of a dam within a watershed influence the distribution of released sediment. Valley confinement, downstream channel gradient, locations and depths of channel pools, locations and geometries of extant channel bars, and locations of other reservoirs all influence the downstream fate of released sediment.

Additional publication details

Publication type Book chapter
Publication Subtype Book Chapter
Title Geomorphic responses to dam removal in the United States – a two-decade perspective
DOI 10.1002/9781118971437.ch13
Year Published 2017
Language English
Publisher Wiley
Contributing office(s) John Wesley Powell Center for Analysis and Synthesis, Volcano Science Center
Description 29 p.
Larger Work Type Book
Larger Work Subtype Monograph
Larger Work Title Gravel bed rivers: Processes and disasters
First page 355
Last page 383