Cost estimating data and tools are needed for dam removal prioritisation, planning, and execution, according to new research in Frontiers in Ecology and Evolution.
Reliable estimates are important for effective decision-making, especially when a portfolio of dams is being evaluated. However, as estimating the costs of decommissioning and removal is a challenge, Duda et al say in their study, it makes it difficult to determine when removal may be a viable alternative to maintaining ageing or problematic dams. Unrealistic estimates, the authors go on to add, can lead to elimination of dam removal as a feasible alternative, create distrust among the public and affected parties, and delay or derail projects.
One of the key difficulties is that a wide range of factors can affect price, along with limited publicly available data to understand their impact on total cost. Factors which can affect price estimates include:
- Size of the dam and its impoundment.
- Geographic setting – rural versus urban.
- Volume of stored sediment and its degree of contamination.
- Presence of sensitive species or infrastructure.
- Requirements for post-removal site restoration, such as stabilisation and revegetation.
- Regional differences in permitting requirements and history of dam removal.
- Need to replace the function of the dam.
- Socio-economic dimensions.
As with dam construction, dam removals can also be swamped by substantial uncertainties, ranging from discovery of unknown structures, contaminated materials, unexpected high flows, or exceeding water quality limits. And then in addition, dam removal can also involve mitigation requirements which influence cost estimation, the scope of which often be hard to predict in the early planning stages.
Whereas cost estimation for civil infrastructure is commonly based on design-bid-build contracts, where the client hires the engineer and contractor under separate contracts, with bids based on unit prices, more complex dam removals may be contracted as design-build projects. Here, the authors explain, the construction contractor maintains ownership of the process from start to finish, and typically bills for the whole project (ie fixed sum or guaranteed maximum price), rather than by unit prices.
“Design-build contracting is more common with complex, large projects that are subject to greater uncertainty, and these contracts tend to avoid changes that occur with the discovery of some unexpected issues that can substantially impact project budget and timeline,” Duda et al state.
Knowledge gap
As the authors reported: “What has been lacking, but greatly needed, in the literature of dam removal is empirical data on the cost of dam removal projects and associated analyses about how the cost varies among dams, their characteristics, and the watersheds and regions in which they reside.”
To address this gap, the authors compiled cost data for 668 dam removals from a variety of sources, showing geographic trends in dam removal costs across the US over the past five decades. The total indexed cost of dam removals was US$1.522B, and assuming such costs were representative of the 1916 dams removed in the US to 2022, the authors estimate the total cost for removing dams on US rivers is in the region of US$4.4B dollars.
Seventy-seven percent of reported costs were for projects where a single dam was removed, whereas 150 dams were removed as part of 53 multi-dam removal projects involving between two and 18 dams. There were far more small dams (542 were less than 5m in height). There were 77 medium height dams (5m–10m), and only 30 large dams over 10m high. Nineteen dams with cost estimates did not have a height estimate. However, the authors suggest it is likely most of the dams lacking height information were less than 5m tall.
With a strong likelihood that dam removal will continue to increase, between 4000 and 32,000 more US dams could be removed by 2050, the authors warn that there “is a pressing need to improve the volume and quality of empirical dam removal cost data to better inform dam removal planning”. Indeed, such data could be coupled with other emerging science and tools that describe how to prioritise, conduct, study, and manage dam removal projects.
As the authors conclude: “A national database of dam removal costs that included component cost breakdowns, the presence of cost drivers aside from construction costs, and accurate demographic data on the dams (eg location, age, height, sediment volume) would dramatically improve the ability to learn from past projects and predict the costs of future projects.”
Geography matters
Meanwhile, in a comparison of experiences when removing dams on the Selune River in France and the Elwha River in the US, Marie-Anne Germaine and Laurent Lespez give an insight into why geography matters in big dam removal projects.
In ecological river restoration projects, geography is still too often analysed mostly as a “study area”, the authors explain. However, it shouldn’t just be invoked here to describe the context of projects, but to analyse environments and their transformations, inviting consideration of the relationships between human and non-human entities.
“Dam removal cannot be reduced to an engineering operation,” they state in their report published in Frontiers in Ecology and Evolution, adding that dam removal “disrupts spatial configurations by removing reservoirs, transforming associated uses, and producing new places”.
Opposition to dam removal
In their research, Boucher and Hudson look at community opposition to dam removal projects. Focusing on the 36m high Vezins dam on the Selune River in France, the authors explain that in 2019 this was the largest dam removal project in Europe. In an effort to restore ecological connectivity and improve water quality, French authorities had ordered removal of this century old structure, but had neglected to foster effective communication with local communities regarding dam removal benefits and riparian stakeholder values.
As the authors state, international, national, and regional-scale actors played influential roles in the French decision to impose the dam removal project upon the local population of the Selune basin. Although often viewed as a positive benefit in many cases, here the dam removal lacked community support. There was strong, and at times even violent, opposition to removing the dams.
The opponents of dam removal included a range of local stakeholders such as politicians, recreational (fishing) interests, small industry, and nature enthusiasts. There was a lack of understanding of how the dam supported a range of valuable local environmental services and economic activities, including nautical, hiking, climbing, photography, firefighter and rescue training, fishing, and drinking water. In addition the flora and fauna that evolved within the dam and reservoir area over the last century was diverse and rich. Economic developments, such as bed and breakfast, fishing shops, had also become part of the local socioeconomic riparian landscape.
“At the core of the opposition is a desire for local stakeholders to work together to clarify concerns that emerged as opponents questioned the consequences of the proposed dam removal based on their local knowledge and lived experiences,” the authors wrote. “The lack of feedback on these concerns and the withholding of information (due to a lack of consultation) crystallized local opposition.”
Boucher and Hudson conclude that the failure of government authorities to effectively incorporate stakeholder values substantially compromises future large-scale federal environmental management projects dependent upon local community support. By examining how local actors experienced dam removal, they add that their study results increase understanding of environmental governance and the local consequences of national policy decisions in future dam removal projects – in France and internationally.
