Dam and reservoir removal projects: a mix of social-ecological trends and cost-cutting attitudes

The removal of dams and reservoirs, while sometimes controversial, is increasingly recognized as a necessary step in modern water management. Rivers have historically been central to human settlements, providing resources and shaping landscapes. However, the last century has witnessed significant anthropogenic impacts, negatively affecting river ecosystems and human well-being. Technological advancements have allowed for greater river control to maximize resource extraction, leading to the transformation of natural river landscapes into anthropogenic ones, a hallmark of the Anthropocene. Globally, a vast number of dams and reservoirs exist, significantly impacting river systems' ecological continuity. A shift toward "green" approaches in water management has spurred dam removal projects, particularly in North America and Western Europe, but the economic and social implications pose challenges. The rationale behind dam removal varies considerably across countries due to differences in political systems, economies, and cultures. This study aims to provide an overview of dam and reservoir removal projects, examining national/regional implications and constraints through various case studies, identifying key stakeholders, their arguments, and attitudes. The study focuses particularly on comparing regionalized attitudes towards the issue in Europe and the US to understand the interplay of social-ecological trends and fiscal attitudes, emphasizing the distinctions between smaller, single-function barriers and large, multifunctional dams.

Wohl (2020) highlights the historical and ongoing dependence of human societies on rivers for various essential resources and services. The author emphasizes the significant negative consequences of anthropogenic activities on river ecosystems. Erickson (2000) exemplifies the large-scale artificial modification of river systems for resource extraction in the Bolivian Amazon. The complex relationship between humans and rivers is further contextualized by the concept of the Anthropocene (ref 4), where human activity fundamentally alters the natural landscape. Existing databases such as the Global Reservoir and Dam (GRanD) database indicate the extensive scale of dam construction globally, with significant implications for the ecological integrity of many river systems (Lehner et al., 2011). Studies by Nilsson et al. (2007) and Grill et al. (2019) highlight the widespread fragmentation and flow regulation of large river systems worldwide, emphasizing the extent of this anthropogenic impact. The paper also cites several other relevant studies (refs 8-16) which illustrate various perspectives on dam construction and removal, including challenges in establishing a universal reasoning for removal, given diverse national contexts (Ding et al., 2019).

The study utilized a mixed-methods approach, drawing upon both qualitative and quantitative data. The researchers identified dam removal studies published before February 28, 2020, using scientific databases (including Google Scholar and ResearchGate), and critically, governmental and non-governmental databases. Four categories of databases were employed: (1) databases with open access, such as those provided under Open Government Licenses; (2) databases maintained by non-profit organizations; (3) databases maintained by various governmental agencies across different countries; and (4) databases from scientific research projects. Specific databases included the National Anthropogenic Barrier Dataset (NABD), National Inventory Dams (NID), USGS Dam Removal Information Portal (DRIP), and others from various countries and organizations (see the complete list in the references). Data extracted from these sources included the number of dams removed, the cumulative number of removals over time, the distribution of dam heights, and reasons for removal. This quantitative data was then integrated with a qualitative analysis of relevant scientific literature to explore the social, economic, and environmental impacts associated with dam removal. The authors performed a graphical analysis of the number of dams removed, cumulative removals, and the distribution of dam heights for removed structures.

The analysis of dam removal projects in the US and Europe revealed significant differences in scale and approach. In the US, between 1968 and 2019, a total of 1654 dams were removed, with approximately 86% being low barriers (≤7.5 m high). The majority of removed dams (86%) were low barriers (up to 7.5 m high), with smaller dams (<2.5 m) accounting for 43%. Approximately 28% of removed dams were used for hydroelectric power generation, 22% for recreation, 14% for freshwater supply, and the rest for various other purposes. The removal of two large dams (32 m and 64 m) on the Elwha River represents a significant project. In Europe, between 1996 and 2019, 342 dams were removed, with 95% being low barriers (≤7.5 m). The study highlighted the lack of uniform data collection across European countries, causing some discrepancies. The increased dam removal activity in Europe, specifically from 2006 onwards, is linked to the implementation of the Water Framework Directive (WFD). Case studies from various European countries (France, Sweden, UK, Spain, Norway, Germany, Netherlands, Finland, and Poland) revealed diverse approaches and stakeholder involvement in dam removal projects. The study notes that the US has a steadily increasing trend in dam removal over time, whereas in Europe the increase occurred primarily between 2006 and 2014 due to EU policy. Differences in dam ownership (private in the US, mostly public or public-private partnerships in Europe) also significantly shape dam management approaches. In the US, safety concerns, especially for low-head dams, were identified as a major driver for dam removal, along with economic factors such as high costs of repair compared to removal. In Europe, the WFD and its focus on ecological restoration of water bodies were shown to be key drivers. The authors identify several challenges, for example the incomplete and inconsistent statistical databases for removed dams across different countries and the lack of uniform data collection across Europe. Additionally, the inconsistent definition of ‘decommissioned’ is highlighted, where sometimes it simply meant lowering the dam or abandoning it, rather than complete removal. High costs associated with the maintenance and repair of dams, especially older structures, compared to the cost of their removal, is another major factor.

The study's findings highlight the complex interplay of social, ecological, and economic factors influencing dam removal decisions. The predominance of small-dam removal across both US and Europe suggests that economic efficiency and safety concerns drive these projects. However, the differing patterns and timelines of removal between the two regions demonstrate the influence of national contexts, regulatory frameworks (like the EU's WFD), and ownership structures. The role of stakeholders (government, environmental organizations, local communities, indigenous peoples, and businesses) and their often-conflicting interests in dam removal decision-making processes is crucial. The contrasting stakeholder involvement in the US (where broad participation is the norm, although it can prolong the process) and Europe (where the decision-making power often rests with public administration) further underscores the regional diversity in dam management. The comparison of case studies from various countries underlines the need for regionally tailored approaches and the significant influence of public policy on dam removal practices. Future research should investigate these regional disparities further and develop standardized data collection methods. Furthermore, the environmental impacts of dam removal, both positive (restoration of river ecosystems, improved fish migration) and negative (sedimentation, release of pollutants) warrant continued investigation. The study suggests a model for decision-making processes based on the more holistic approach in the US.

This review underscores the lack of comprehensive global data on dam removals, with significant regional variation in data collection practices. While the removal of small dams is common due to low economic benefit and cost-effective removal, large dam removals remain less frequent and driven by technical problems or abandonment. The study emphasizes the importance of considering multiple social, economic, and environmental factors in dam removal decisions, highlighting the need for integrated approaches and stakeholder engagement. Future research should focus on developing standardized data collection methods, examining the long-term ecological effects of dam removal, and refining decision-support tools to effectively balance ecological restoration with social and economic considerations.

The study acknowledges limitations stemming from the incomplete and inconsistent statistical databases for dam removals across different regions. The data used was based on available information, which may not be entirely comprehensive, resulting in potential biases. The lack of standardized definitions for dam decommissioning across countries also limits the direct comparison of data. The study's analysis is primarily based on existing data, limiting the ability to draw definitive causal links between specific factors and dam removal decisions.