Example IDAM analysis for hypothetic dam scenarios in Columbia River Basin (Brown et al. 2009)
Scenario: High Impact Dam
This hypothetical new dam site is located on the main stem of a large river in the Unites States, with the primary objective of providing a reliable source of irrigation water and a secondary objective of producing hydropower. It is a wide (820 m) and relatively short (21 m) structure, blocking passage for three species of endangered salmon as listed under the Endangered Species Act (ESA) to an 88 km spawning habitat and leaving 18 km dry downstream during very dry years.
Because of the generally low slope of the river valley, the reservoir will have a high surface area and will inundate two Native American reservation communities comprising nearly 1000 people in total. Archaeological digs have recently discovered artifacts of a community dating back to 2200 years within the inundated area, and sites of spiritual importance will be submerged. The residents of the affected communities will be relocated outside of the valley to a reservation in the dry grassland 200 km away. Water is not immediately accessible at the relocation site, but the U.S. government has agreed to dig wells for the displaced communities. However, no agreements have yet been signed between the communities and the federal government because the residents are concerned that the wells will be insufficient to meet their water needs. Employment opportunities will exist at the new reservation in the form of a newly constructed casino. Educational programs will be developed at the new site for the relocated residents.
The benefits and costs of this high-impact dam are described in the IDAM circles presented in Fig. 3. Note that the objective metrics and subjective valuations have been estimated for this hypothetical dam for illustrative purposes (see Table 5 for detail); for a true IDAM evaluation, a decision-making team must provide the data for metrics and valuations. In addition, recall that an impact without shading implies that there is no objective impact and/or that the subjective valuation associated with that impact is zero. Subtracting the total cost (Panel B) from the total benefit (Panel A)
in the IDAM tool indicates a net cost of 10 units as follows: net cost of 58 units to biophysical impacts; net benefit of 23 units to socioeconomic
indicators; and net benefit of 25 units to geopolitical indicators. This outcome is compared to the net benefit (or cost) of a low-impact dam built on a tributary of the dam below.
Magnitude of impact is measured along the arc of each pie piece, while the subjective valuable of the impact is represented by the radius length of each impact. From this hypothetical example, a great disparity between overall costs and benefits is not evident, though the amoeba diagrams indicate that while a bulk of the costs (left) are imposed on biophysical and socio-economic elements of the study community, the benefits tend to be applied to socio-economic and geopolitical elements of the study community. These graphs, along with spatial mapping of the costs and benefits, can useful for evaluating hypotheses about distribution of dam impacts.