Prioritizing dams for removal to advance restoration and conservation efforts in the western United States

Abstract

Dams are socio‐ecological structures fundamentally serving human population growth and economic development. Yet, dams have significantly reduced landscape connectivity, altered hydrologic and geomorphic dynamics, and are a leading cause of freshwater biodiversity decline. As dams age and are no longer used for their original intended purpose, they increasingly threaten both humans and ecosystems. Consequently, dam removal is an increasingly accepted strategy to restore river systems across the United States; since the 1970s, more than 1,400 dams have been removed. As the removal trend continues, important decisions must be made regarding which dams are still ecologically and economically viable and which are optimal for removal to facilitate restoration and subsequent protection. Therefore, it is critical to prioritize dams for removal where rivers, freshwater resources, and ecosystem services will benefit most. To that end, this study uses geospatial analysis and a multi‐criteria decision framework to evaluate dams suitable for removal in the western United States in watersheds with existing conservation priorities, and to examine watershed dynamics in which they are situated. Results reveal 24 top‐ranked dams no longer performing essential ecological and social functions as optimal sites for removal to restore waterways. Of these top‐ranked dams, four are already in the planning process for removal, indicating the model is performing as intended. These results are critical for managers and policymakers to understand where dam removals could enhance overall riverine connectivity and where river restoration could result in subsequent protection of newly free‐flowing river segments in the National Wild and Scenic Rivers System.

How Does Flow Alteration Propagate Across a Large, Highly Regulated Basin? Dam Attributes, Network Context, and Implications for Biodiversity

“…Leveraging network context‐dependencies, instead of ignoring them, could be an important step toward informing river ecosystem restoration via dam operation. This shift could also be important for prioritizing dam decommissioning (Guetz et al., 2021), or for mitigating socio‐environmental impacts in global regions where dam construction is underway (Flecker et al., 2022; Holtgrieve & Arias, 2022).…”

Six years of fluvial response to a large dam removal on the Carmel River, California, USA

“…These findings can inform future efforts to restore rivers by removing dams, given the growing international interest in this approach (Birnie‐Gauvin et al, 2020; Habel et al, 2020; Ibisate et al, 2016; Maxwell et al, 2021; Ravot et al, 2020; Wang & Kuo, 2016). Environmental planning of rivers, not only through dam removal but also dam renovation and revised operations, will remain a major application of fluvial geomorphology in an era of changing hydroclimate and the need for non‐fossil‐fuel energy (Chartrand, 2022; Curry et al, 2020; Guetz et al, 2022; Kondolf & Yi, 2022; Zarfl et al, 2015), as will proactively removing dams that are safety hazards (Vahedifard et al, 2020). We encourage additional research into the effects of these actions on river channels, even when geomorphic responses are not dramatic, to expand the literature base on which environmental management decisions are made.…”

Reviving Europe's rivers: Seven challenges in the implementation of the Nature Restoration Law to restore free‐flowing rivers

“…Aligned with our recommendations for addressing Challenges 1-3, we advocate a prioritization approach that considers not only physical location, ease of restoration, and economic factors but also expected ecological outcomes (see also Guetz et al (2022)). Given this perspective, the NRL's proposal to prioritize the removal of obsolete barriers first may seem contradictory.…”

“…Depending on the system, restoration goals can range from initiating hydromorphic dynamics and ecological succession (e.g., in floodplains and wetlands) to maintaining a desired flow regime in free‐flowing rivers. For restoration efforts such as dam removal to have a meaningful impact, it is critical to focus on areas where restoration efforts will result in the most substantial improvements to ecological conditions, freshwater resources, and ecosystem services (Erös et al, 2018; Guetz et al, 2022). According to the NRL, restoration efforts should focus primarily on obsolete barriers that are no longer required for renewable energy production, inland navigation, water supply, or other uses (Article 7.2).…”

“…Yet, cost efficiency should be weighed against the long‐term benefits of restoration, that is, habitat quality, biodiversity, and ecosystem functioning (Costea et al, 2021). Furthermore, using prioritization methods such as those discussed in Erös et al (2018), Guetz et al (2022), or proposed by expert working groups (such as WG ECOSTAT in the EU) can help with decision‐making.…”