“As scientists we tend to look at things through our own tiny little drinking straw, studying our one narrow field,” says Bryan Tilt, Associate Professor of Anthropology at Oregon State University in the US. “When it comes to dams we felt a broader perspective was needed. Because when you put up a dam it affects whole ecosystems and whole communities.

“I’m most interested in understanding and mitigating the impacts of dams on communities, economies and cultures,” Tilt explains. “But it turns out that it’s impossible to separate these social impacts from the effects of dams on ecosystems, water quality and availability, and interregional or even international relations.”

Tilt was speaking about his involvement in what has been described as the first of its kind: the development of a new system to help policy makers better assess the costs and benefits of building dams. By using an interdisciplinary approach the distribution of biophysical, socio-economic and geopolitical impacts of dams can be evaluated by the one modelling system.

As Aaron T Wolf, Professor of Geosciences at Oregon State University adds: “Having one tool that helps synthesise and visualise all of the complex impacts that dams have on the human and natural landscapes, not only will contribute to better decision making, but will also lead to healthier conversations.”

The system in question is called the Integrative Dam Assessment Modelling (IDAM) tool. Developed by an interdisciplinary team of scientists from Oregon State University and Hobart and William Smith Colleges, the impetus for the project was the World Commission on Dams’ final report in 2000.

IDAM’s goal is to support more informed and transparent decision-making processes related to dam development in any area. “The fact is that China and African, Southeast Asian and Latin American countries are building dams at an amazing pace right now,” Tilt comments. “There is no denying that they are going to continue to build them for the near future. So how can we help them do it better, more sustainably, and mitigate any damage as much as possible?”

“We were originally inspired by the belief that there is so much to gain by investigating water resources solutions as interdisciplinary teams,” says one of the project’s leaders Desiree Tullos. “But it was the recommendation by the World Commission on Dams which called for a comprehensive options assessment in decision making on dams, that led us to begin thinking about how such a framework might be structured, and then to seek support from the National Science Foundation to begin developing, evaluating, revising and applying it.”

In 2007 the National Science Foundation funded research by the team to develop and test the dam assessment tool. Its application focused on hydropower development in the Yunnan Province of China to study how impact distributions vary across disciplines, space and stakeholder groups in the country. “We analysed the interdisciplinary impacts of centralised and decentralised hydropower development and regional planning,” Tullos says. “And we characterised how salience influences decision making about dams.”

One obvious question, Professor Tilt remarks, is why the concept of ‘salience’ matters in hydropower decision making? “The answer is simple,” he says. “Different groups often have different ideas about which outcomes of a dam development project are most important. The results of focus groups and surveys from two continents confirm this. It’s understandable that different stakeholders have different perspectives; but what we want to do is to capture those different perspectives, to make them explicit, and to represent them with transparency in the decision making process.”

How does IDAM work?

The 1992 United Nations Conference on Environment and Development identified biophysics, socio-economics and geophysics as the primary areas of concern for environmental and social sustainability in development. As the impact of dam construction may be felt across these areas, the Integrative Dam Assessment Modelling combines the three themes into two circle diagrams, one measuring the costs associated with proposed dam development and the other measuring the benefits.

The IDAM tool works by analysing 21 different impacts, seven from each of the three systems below:

• Biophysical Impacts: How does a given dam project affect the environmental aspects of a river ecosystem?

• Socioeconomic Impacts: How does a given dam project affect human communities, economies and cultures?

• Geopolitical Impacts: How does a given dam project affect natural resource decision making, governance and inter-state relations?

Each impact consists of two parts: magnitude, which is the objective measure of severity of that impact on a 1-5 scale; and salience, which is the subjective importance or significance assigned to the impact, also on a 1-5 scale, by a group of stakeholders. The IDAM tool features a graphical user interface that allows users to input data for a given hydro development scenario, and to compare different scenarios. The model can be modified to suit the characteristics of different dam projects.

Its developers claim that IDAM provides a number of previously unavailable benefits to decision makers and stakeholders regarding dam development. These include:

• In line with the WCD’s call for more comprehensive options assessment, IDAM allows users to assess the effects of dams more holistically on biophysical, socioeconomic and geopolitical systems.

• It is visually accessible and allows users to see how the benefits and costs of a given dam project are distributed across these three systems.

• It combines objective, scientific analysis on the magnitude of impacts with the subjective salience assigned by stakeholders to those impacts, making the decision making process more equitable and transparent and allowing users to understand how and why different stakeholders might value different outcomes.

• IDAM allows stakeholders to make explicit comparisons between different hydro development scenarios; users can compare different watersheds, different dam designs, and different operational characteristics to see the various impacts associated with each scenario.

By providing a visual representation of the various costs and benefits associated with two or more dams, decision makers can evaluate alternatives and articulate priorities associated with a dam project. They can then begin to think systematically about how to select the best option or how to mitigate the most serious negative impacts of a scheme.

A key element of IDAM is that the framework makes individual salience explicit and transparent. “This element alone has facilitated important discussions and highlighted fundamental differences between stakeholders,” Tullos says. “The salience element is what makes it different from other decision analysis tools. But it is really intended to be complementary to other decision analysis approaches.”

Darrin Magee, Assistant Professor of Environmental Studies at Hobart and William Smith Colleges, adds: “We recognise that the tool and the theoretical framework on which it rests are imperfect, but we hope they will serve as a foundation on which better ones may be built.”


One disadvantage of the IDAM tool is the considerable up-front data requirements for the objective assessment of dam impacts. Although any thorough evaluation of dams such as environmental and social impact assessments is based on almost identical information, the IDAM tool makes the data needs clear at the outset.

A second potential limitation of the tool is that the 21 individual impacts may not be appropriate to every setting. Although those involved in the project have endeavoured to make the categories widely applicable it is expected that some decision makers may find it useful to adapt them to the local context.

The value of the IDAM tool depends on a balanced treatment of each disciplinary perspective. If natural scientists or environmentalists comprise a disproportionate share of the decision making team, for example, the socio-economic and geopolitical costs and benefits of dams may be undervalued, leading to biased evaluations. Finally, the tool requires consensus building among interested constituencies. The developers of the model view this as an advantage but believe that some decision makers may disagree.

“We see IDAM as an important step toward quantifying, valuing, and visualising many of the aspects of dam sustainability that tend to get overlooked, precisely because they are difficult to quantify, value, and visualise,” Magee says.

Properly implemented, the team of scientists involved in the development of IDAM believe that the tool encourages consensus building and affords an opportunity for heuristic decision making. Furthermore it will help to advance understanding of how dams affect human and ecological systems.

“As scientists we’re not in the business of advocating any particular policy position,” Tilt concludes. “For us the main goal is to help provide a holistic, interdisciplinary and transparent assessment of the impacts of hydropower development.”

The Integrative Dam Assessment Modelling team are currently polishing up the computer programme which runs the model, plus writing technical documentation explaining how to use it. IDAM should be publically available in early 2012. For more information contact Bryan.Tilt@oregonstate.edu

IDAM’s principal investigators

* Bryan Tilt – Associate Professor of Anthropology at Oregon State University (OSU). Tilt is an environmental anthropologist who studies the social and environmental impacts of rural development, with a special focus on China
* Desiree Tullos – An Associate Professor in the Department of Biological & Ecological Engineering at OSU, Tullos is an environmental engineer with expertise in ecohydraulics and hydraulic modelling.
* Darrin Magee – Assistant Professor of Environmental Studies at Hobart and William Smith Colleges. Magee is a geographer specialising in energy and water issues in China.
* Aaron Wolf – A professor of Geography at Oregon State University. Wolf studies water resources policy and conflict resolution.