by Andrew L. Rypel, Christine A. Parisek, Jay Lund, Ann Willis, Peter B. Moyle, Sarah Yarnell, Karrigan Börk
Damming rivers was once a staple of public works and a signal of technological and scientific progress. Even today, dams underpin much of California’s public safety and economy, while having greatly disrupted native ecosystems (Quiñones et al. 2015, Moyle et al. 2017), displaced native peoples (Garrett 2010), and deprived residents of water access when streamflow is transported across basins. California’s dams are aging and many will require expensive reconstruction or rehabilitation. Many dams were built for landscapes, climates and economic purposes that no longer exist. California’s current dams reflect an accumulation of decisions over the past 170 years based on environmental, political, and socio-economic dynamics that have changed, sometimes radically. Former Secretary of the Interior Bruce Babbitt remarked, “Dams are not America’s answer to the pyramids of Egypt… Dams do, in fact, outlive their function. When they do, some should go.”
Is California prepared for updating or removing this infrastructure, and what would be the consequences of inaction?
We examined the National Inventory of Dams (NID) to assess the state of California’s dams. This database is a large data product curated by the US Army Corps of Engineers and contains information on most large dams in the USA (Fig. 2, 3, Table 1). Across the nation there are 91,468 NID dams, with 1,580 in California. Because there are multiple dams on some reservoirs, we estimate a total of 80,101 and 1,444 NID reservoirs in the USA and California, respectively.
Mean age of USA dams is 59 years old; but mean age of California dams is 72 years (Fig. 3). The 25% oldest CA dams are 93 years or older. California’s total reservoir storage capacity behind NID dams is 45 million acre-feet with a total reservoir surface area of 713,146 acres. For comparison, the total surface area of all managed natural lakes in Wisconsin is 943,130 acres, supporting a massive tourism industry (Rypel et al. 2019). Unfortunately, 1,097 (69%) of California NID dams are listed as high or significant hazards to human communities if they fail (Fig. 2, Table 2). These counts greatly underestimate problematic dams. In the USA, there are hundreds of thousands of smaller (often old) dams that fall outside of state and federal lists, and so are not included in the NID. This issue is broader than just dams too – infrastructure of all varieties is aging, representing a growing problem for humans and wildlife (Börk and Rypel 2020).
We have already witnessed examples of the high cost of inaction. Recently in Michigan, two dams (Edenville and Sanford) failed and forced the evacuation of 10,000 residents in the midst of the COVID-19 pandemic – essentially a worst case scenario. Extreme rain in the midwest led to historic flooding in the Tittabawasse and Tobacco Rivers. Federal regulators had worried about failures at the Edenville Dam for 30 years due to an undersized spillway (see related news stories 1, 2, 3, 4).
Table 1. Summary statistics on age and storage capacity of dams and reservoirs in the USA and California.
In California, we recall a near miss when the Oroville Dam spillway failed in early spring 2017. Floods damaged the primary spillway such that the California Department of Water Resources stopped flow over the spillway to better assess damage. Lake levels continued to fill and ultimately overtopped the emergency spillway, triggering unexpected erosion around the emergency spillway and the evacuation of 188,000 residents downstream. An independent forensic report of the Oroville incident highlights several lessons, including the need for periodic review of dam design and performance. Dams in California have failed before and a list of major events can be found here and here. Recent evaluations have indicated that conditions of California dams are below average, with one reporting a statewide grade of “C-” (Moser and Hart 2018; https://www.infrastructurereportcard.org/state-item/california/).
Table 2. Summary of hazard classifications for USA and California dams based on the NID. The NID defines hazard potentials as: “High” – dam failure is likely to result in loss of human life. “Significant” – likely no risk to human life, but a likelihood to cause economic and/or environmental losses. “Low” – likely no risk to human life and low anticipated economic and/or environmental losses. “Undetermined” – hazard designation not assigned; here, dams classified as “undetermined” were grouped with dams that had an N/A hazard potential.
Dams also can have catastrophic effects on natural ecosystems, especially in productive and species-rich large rivers (Poff et al. 1997). Dams fragment the hydrologic connectivity of ecosystems, and create massive physical barriers for migratory species, including salmon. American rivers are so extensively fragmented by dams, that Benke (1990) estimated only 42 high quality free-flowing rivers remain in the USA – zero in California. In the Sacramento Valley, abundant spring-run Chinook salmon would once migrate long distances and over-summer high in cold mountain streams. Now, spring-run Chinook salmon are listed under the US Endangered Species Act, largely because of disruptions from dams. In the San Joaquin River, construction of Friant Dam preceded a rapid eradication of spring-run Chinook from this ecosystem. Expensive efforts to reintroduce spring-run Chinook salmon hold promise; but fish are still fundamentally blocked from naturally cold habitats by rim dams. The McCloud River once had all four runs of Chinook salmon, plus steelhead and bull trout. None of these species occur in the McCloud River anymore, and bull trout have gone extinct in California. Helfman (2007) suggested that ~70% of global freshwater fish extinctions can be attributed to “habitat change,” including effects of dams.
Beyond the catastrophic failures and ecological impacts of individual dams, California’s dams create disastrous outcomes for disadvantaged communities, including Native American Tribes. Tribes along the Klamath have spent years struggling to preserve the river and its sensitive salmon populations. Removing deadbeat dams like the four major dams on the Klamath River along the CA-OR border exemplify the types of projects where removal makes economic sense to dam owners and begins to address damage to indigenous communities of color and aquatic ecosystems. NGOs have long been interested in dam removals like this. However, the slow speed of these removals highlights the complicated details involved in removal. Such experiences suggest efforts addressing aging dams must start early.
The California Division of Safety of Dams (DSOS) has existing responsibilities that include: 1) Performing independent analyses to understand dam and appurtenant structures performance; 2) Overseeing construction to ensure work is being done in accordance with approved plans and specifications; and 3) Inspecting dams on an annual basis to ensure it is safe, performing as intended, and is not developing issues. Roughly 1/3 of these inspections include in-depth instrumentation reviews of the dam surveillance network data. Every state (except GA) has a dam safety program, and the CA program is the largest in the USA. Therefore, the DSOD plays a major role in working with dam owners to identify deficiencies in California. The size of the DSOS program suggests this resource could be leveraged in CA to take a leading role in dam safety. Response to aging dams has been mostly reactive. Studies of dam behavior during earthquakes has been a long focus of research, and such questions are obviously important in California. In a 1977 USGS analysis of dam structural behavior during Earthquakes, half the study systems were in California. Many of the major dam failures in California were triggered by earthquakes.
California is well-positioned to lead in proactively addressing aging dams; however, the window for leadership is likely closing. The challenge will be in developing balanced approaches that prioritize the dams, rivers and people in most need of help (Null et al. 2014). To advance policy on dealing with obsolete dams, we suggest California should:
(1) Form a “California Dams Blue Ribbon Panel”. Given recent experiences in California and nationally, it seems timely for the State of California to take stock and assess the long-term performance of its dam regulation capabilities. Efforts are needed to assist the public, local governments, and dam owners in identifying at-risk dams in need of action. A California dams blue ribbon panel would help develop a framework for decision making that could be applied to dams across the state. The panel’s charge would be to: i) evaluate the state’s existing regulatory framework for evaluating public safety and environmental performance of dams; ii) estimate overall magnitude of current and future dam safety and environmental problems (especially with climate change); iii) recommend improvements to state regulatory capacities and support for owners in terms of dam safety and environmental performance. Panel findings might be published as a white paper for others to use and reference. The panel should have broad representation from multiple stakeholder groups including roles for Native American tribes and other disadvantaged and at-risk communities. Ultimately, a blue ribbon panel and white paper format would produce faster results than a larger task-force style effort, but could lead to a larger effort if necessary.
(2) Develop a structured assessment tool. An objective science-based prioritization framework would be useful. Structured assessments are a class of tools that can more transparently and objectively analyze natural resource management decisions in a careful and organized way (Gregory et al. 2011). Such models are popular in some federal agencies and have already aided decision-making in other areas of CA state government, such as welfare services. A directed action to build such a tool could rapidly aid agencies charged with managing aging dams and scoring restoration projects. Once the tool is available, proposed on-the-ground restoration projects could be scored more transparently. Projects that propose work on high priority dam sites might then be prioritized for funding. Thus restoration projects funded through state bond propositions (e.g., Prop 1 and Prop 68) net the state and its investors the most “bang for their buck”, while simultaneously leveraging science and enhancing transparency and accountability. Improvements to the assessment method could form a way of incorporating new scientific findings or ways of thinking over time.
(3) Revisit existing legal frameworks. Dams sit at the crossroads of state and federal law and so face a complex mess of state and federal laws and regulation. Prominent legal issues will include liability for flooding and for environmental damages associated with dam removal (which will differ between privately and publicly owned dams), environmental reviews mandated under state and federal endangered species and environmental impact laws, and the myriad dam-specific laws. This is an area of active research in environmental law (see here recents legal debates on issues facing dams in the Western USA). Some examples of laws that have legal relevance to the operation and use of dams include the California Fish and & Game Code 5937 – “Water for Fish” (Börk et al. 2012). Additionally, under the authority of the Federal Power Act, the Federal Energy Regulatory Commission (FERC) retains exclusive authority to license non-federal hydropower projects on navigable waterways, federal lands, or areas connected to the interstate electric grid. Opportunities for dealing with deadbeat dams also present themselves during the FERC relicensing process. Indeed this was a critical piece to the removal of the Klamath Dams. Most dams currently face little regulation and receive little attention from policy makers.
(4) Explore reservoirs as novel habitats for declining fishes. Because many California reservoirs contain expansive coldwater habitats, scientists have occasionally suggested reservoirs could be capable of serving as emergency rooms for declining native fishes. Some California reservoirs have developed self-sustaining populations of Chinook salmon (Perales et al. 2015). These populations may be needed as a backup plan in the event a disease or other disturbance afflicts the primary Sacramento River salmon runs. We support this concept and note that some reservoirs and dams may hold hidden value in this regard. Reservoirs successfully managed as novel habitat for native fishes might ultimately be scored higher for dam renovation or repurposing funds.
Every dam is unique and there will be no one-size-fits-all approach. Ultimately dams are owned by entities ranging from the state of California, water agencies and districts, counties, cities, homeowner’s associations, private companies, or private citizens. Hansen et al. 2020 identified that in general dams can be mitigated, renovated, repurposed, or eliminated. In California, dams have been important in controlling water availability, both reducing the frequency of catastrophic floods and making water available for cities and irrigated agriculture in our highly variable Medeterranean climate. They will remain vital in the future, perhaps even more so with anticipated changes in climate. Ultimately, some dams will be fine, some will need to be removed, and some modified. At this point however, an overarching strategy is needed to guide efforts to identify which dams are suited to our uncertain future and which are more risky than worthwhile, then rank them with the best rubric we can devise (e.g..Quiñones et al. 2015). Planning for aging dams is not unlike planning for a pandemic. It seems as though you don’t need it…until you do.
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