Dam removal: Listening in

Abstract

Dam removal is widely used as an approach for river restoration in the United States. The increase in dam removals—particularly large dams—and associated dam‐removal studies over the last few decades motivated a working group at the USGS John Wesley Powell Center for Analysis and Synthesis to review and synthesize available studies of dam removals and their findings. Based on dam removals thus far, some general conclusions have emerged: (1) physical responses are typically fast, with the rate of sediment erosion largely dependent on sediment characteristics and dam‐removal strategy; (2) ecological responses to dam removal differ among the affected upstream, downstream, and reservoir reaches; (3) dam removal tends to quickly reestablish connectivity, restoring the movement of material and organisms between upstream and downstream river reaches; (4) geographic context, river history, and land use significantly influence river restoration trajectories and recovery potential because they control broader physical and ecological processes and conditions; and (5) quantitative modeling capability is improving, particularly for physical and broad‐scale ecological effects, and gives managers information needed to understand and predict long‐term effects of dam removal on riverine ecosystems. Although these studies collectively enhance our understanding of how riverine ecosystems respond to dam removal, knowledge gaps remain because most studies have been short (< 5 years) and do not adequately represent the diversity of dam types, watershed conditions, and dam‐removal methods in the U.S.

Rapid Recolonization and Life History Responses of Bull Trout Following Dam Removal in Washington's Elwha River

“…); after dam removal, higher‐salinity habitats migrated seaward from the historic estuary complex to the newly formed delta (Foley et al. ).…”

“…; Foley et al. ), and restoring connectivity can increase the abundance, spatial distribution, and life history diversity of migratory fishes (Hitt et al. ; Pess et al.…”

Using Structured Decision Making to Overcome Scale Mismatch Challenges in Barrier Removal for Watershed Restoration

“…The removal of barriers, such as dams and culverts, has become a commonly used approach in river restoration to re‐establish the connectivity of river flow, sediment, and species movement (Foley et al. 2017a). These removals have resulted in increases in native species richness, diversity, and productivity (Foley et al.…”

“…These removals have resulted in increases in native species richness, diversity, and productivity (Foley et al. 2017a). Barrier removal is also used to restore commercially important or threatened migratory fish, such as salmonids (family Salmonidae), alosines (family Clupeidae), sturgeons (family Acipenseridae), Sea Lamprey Petromyzon marinus , and freshwater eels Anguilla spp., by improving the connectivity between feeding and spawning habitats (Pess et al.…”

Multidecadal Geomorphic Evolution of a Profoundly Disturbed Gravel Bed River System—A Complex, Nonlinear Response and Its Impact on Sediment Delivery

“…We have learned much by analyzing fluvial responses to past events. Studies have shown that geomorphic responses to fluvial disturbances (1) relax over varying timescales but can persist for years to decades, even centuries; (2) can be both acute and gradual; (3) are influenced by many factors including hillslope‐channel coupling, physical linkages among channel reaches, and hydrological regimes; (4) can follow many trajectories; (5) are intricately intertwined with ecological recovery; and (6) that systems may not return to predisturbance states (e.g., Bellmore et al, ; Cluer & Thorne, ; East et al, ; Foley et al, ; Gellis et al, ; Gran et al, , ; James, ; James & Lecce, ; Kasai, ; Kasai et al, ; Major et al, ; Moody & Meade, , ; Pierson & Major, ; Schumm, ; Swanson & Major, ). But we can further exploit records of physical responses to profound fluvial disturbances to gain richer geomorphic insights.…”