By Suman Jumani, Ted Grantham, Lucy Andrews, Jeanette Howard
California has a dam problem. Since the start of the 20th century, the state has built thousands of dams on its rivers and streams. Now, more than 75% of the largest dams (totaling over 900) are greater than 50 years old, and the mean age is close to 80 years old. This means that a significant proportion of the state’s dams are reaching – or have already reached – the end of their designed lifespan. Many are no longer performing their intended functions due to sediment build-up, lack of maintenance, or obsolescence. What do we do about these “deadbeat dams”? As discussed in an earlier post, given the poor condition of many of these dams, and the often devastating consequences of their failure, doing nothing is not a good option. So, the authors of that article suggest California take a proactive approach. In particular, they cite the need for a “structured assessment tool” to assess the risks of aging dams and help identify those whose time for removal has come.
In a paper, recently published in Environmental Challenges, we present a decision-support tool for dam-removal planning in California. It is designed as a multi-criteria evaluation framework that considers the broad suite of economic, environmental, and social factors that influence dam removal decisions. Expanding upon previous dam removal assessments in the state (e.g., Quiñones et al. 2015), the framework helps to identify dams for which removal would:
- Be opportunistically viable and improve safety without losing critical services (Tier 1),
- Result in improved riverine ecosystem integrity, function, and biodiversity (Tier 2), and
- Be beneficial or acceptable to local communities (Tier 3).
The first objective (or Tier 1) is achieved by identifying dams that are financially and opportunistically feasible to remove. These include relic dams that no longer provide beneficial functions, such as water supply or flood control. It also includes dams in poor physical condition that pose a safety liability. In addition, the screening process flags smaller dams, which may be less expensive or complex to remove than large dams, and those undergoing hydropower relicensing, which presents a formal opportunity to evaluate a dam decommissioning alternative.
River restoration is another compelling reason to remove dams. Tier 2 of our evaluation framework identifies dams whose removal would significantly improve river connectivity and restore more natural flow regimes to benefit a range of freshwater species, especially migratory fishes. In California, this means prioritizing dams whose removal would restore passage for salmon, steelhead, and other anadromous fish runs. Tier 2 evaluation criteria also favor dam removals in catchments that support high habitat diversity and are expected to be more resilient to climate change. Finally, this tier takes into account two potentially adverse environmental effects of dam removal: mobilizing reservoir sediments containing mercury and the potential for spreading invasive species either above or below dams.
All criteria are assigned user-defined weights and aggregated as Tier 1 and Tier 2 scores for individual dams. When applied to a population of dams, it is possible to plot these scores independently to distinguish dams whose removal appears opportunistically feasible and ecologically beneficial (i.e., “good candidates”), from those which have relatively limited environmental benefits and/or are unlikely candidates for removal given the important services they provide (i.e., “poor candidates”). It is also possible to estimate the cost of dam removal based on the size and costs of removing similar dams in the past (Duda et al. 2023).
Ultimately, dam removal decision-making lies within the social and political realms. Therefore, a set of additional (Tier 3) criteria are included in the framework to assess community perceptions and attitudes about dams of interest and to consider how dam removal could affect recreational, economic, and cultural values. Unlike the Tier 1 and Tier 2 assessment, this requires outreach to local communities, organizations, and governments to evaluate the feasibility of dam removal.
Overall, our approach can help identify ‘low-hanging fruit’ – especially deadbeat dams whose removal addresses public safety risks, provides environmental benefits, and has the support of local communities (for example, York Dam in Napa County). The framework is also intentionally flexible, allowing for the addition or exclusion of specific criteria, or weighting of specific objectives to reflect the values and priorities of those using the tool.
We envision this tool being applied to assess removal potential of dams within a watershed or a region. For instance, in our paper, we applied the framework as a ‘proof-of-concept’ to California’s North Coast region to assess the removal suitability of 25 large dams > 50 years old. We identified dams that could be opportunistically and ecologically beneficial to remove, including Cape Horn dam on the Eel River which is currently being proposed for removal by Native American tribes, non-profit organizations, and community groups. We did not examine Tier 3 criteria in depth, but suggest the dams flagged as “good candidates” be further analyzed for removal potential. In our assessment, we also identified 10 “poor candidates”, several of which were associated with higher monetary costs of removal.
In developing and applying this framework, we encountered several notable data gaps. The most critical is the lack of a unified state dam database. Currently, California’s Division of Dam Safety and U.S. Army Corps of Engineers maintain a list of large dams in the state, but there are thousands of smaller dams (such as those reported in the Passage Assessment Database) that are not included in the state’s inventory. Furthermore, information about dam seismic safety risk, degree of reservoir sedimentation, contaminant levels, and presence of invasive species are not systematically reported or included in the state’s dam database. Given the widespread occurrence of aging dams in the state, there is a need for the state to invest resources in better characterizing dams to inform decisions over their future rehabilitation or removal. In the absence of such information, the risks of aging dams to people and the environment will continue to grow as prospects for a strategic and holistic approach to dam removal diminish.
Suman Jumani is a postdoctoral fellow at the Environmental Lab of the US Army Engineer Research and Development Center. Ted Grantham is an Associate Professor of Cooperative Extension in the Environmental Science, Policy, and Management Department at UC Berkeley. Lucy Andrews is a PhD candidate at UC Berkeley. Jeanette Howard is the director of science for The Nature Conservancy’s California land science team.
Duda, J. J., Jumani, S., Wieferich, D. J., Tullos, D., McKay, S. K., Randall, T. J., Jansen, A. (2023). Patterns, drivers, and a predictive model of dam removal cost in the United States. Frontiers in Ecology and Evolution, 11, 1215471.
Jumani, S., Andrews, L., Grantham, T. E., McKay, S. K., Duda, J., & Howard, J. (2023). A decision‐support framework for dam removal planning and its application in northern California. Environmental Challenges, 12, 100731.
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