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Content 2. Defining water requirements 3. Modifying water infrastructure 5. Creating a policy and legal framework 6. Generating political momentum  |
3.4
Decommissioning Infrastructure to Restore Environmental Flows The last phase of the project cycle involves a choice of decommissioning or life extension. Many countries have dams approaching the end of their economic life. For these a decision about life extension or removal is required. Often, the public perception is that removal is a radical idea. It is certainly opposed by some stakeholders. However, the removal of infrastructure that has exceeded its economic life is a normal consideration and dams are no exception. "REMOVING A DAM CAN BE LESS EXPENSIVE THAN REPAIRING IT." Where it is no longer in the public interest, or economically or financially viable, to operate and maintain the dam, removal is an option where it is physically feasible to do so. Experience shows that removing a dam can be less expensive than repairing it, particularly when the services the dam had provided are limited. Changing social values that call for restoration of river flows and ecological services, public safety, reduction of legal liability from a hazard that is uneconomical to repair are all factors that have influenced past decisions to decommission a dam. There are about 500 examples of partial and full decommissioning of dams in North America and Europe. Dams have been removed serving purposes ranging from hydroelectric to flood control and water control. These dams were of various types, including earth fill dams, concrete arch dams and masonry dams. To date, the average height of dams removed in the United States is about 6.5 metres. About 10 percent of the dams removed were over 12 metres, and four dams removed were over 36 metres.63 The next boxes provide examples of decommissioning projects and studies to restore environmental flows. 3.4.1 Options for Decommissioning The options for decommissioning depend on the type of dam and the basin context. Broadly, the three main approaches are:
Opening the gates is a low cost option. It is feasible in run-of-river dams or storage dams with full-length sluice gates. For example, after a cabinet decision the gates of the Pak Mun dam in Thailand were opened in 2000 to restore fish migration in the Mun River, a tributary of the Mekong River. This measure was taken pending a full assessment of the impact of the dam operation on the migration of various species of fish. Partial removal may be appropriate when the dam is constructed in different sections, for instance, with parts earth fill and parts concrete structures. In these cases, it may be economical and safe to remove only one segment of the dam. Full removal is generally more expensive and often involves the reversal of the procedural steps taken to construct the dam. Broadly, the main costs of decommissioning are those associated with:
In economic terms, the benefits derived from restored ecosystem services would be subtracted from the cost of decommissioning. In practice, decommissioning itself can be straightforward and accomplished quickly. Alternatively, it may be staged over several years, particularly when special care is needed to manage sediments that have built up over time in the reservoir.
This 15m high concrete dam on the Léguer River
was built in 1920 to supply power to a paper plant. The 400,000 m3 reservoir
located downstream of agricultural areas, experienced extensive 3.4.2 Typical Limitations, Responses and Risks Most advocates of decommissioning recognise that it is not appropriate for all large dams. Broadly, the larger the dam and reservoir the less feasible decommissioning becomes. At some stage, the costs and physical limitations become prohibitive. In a water-deficit basin, for example, decommissioning of a major storage dam would not be a viable option in the foreseeable future. Nevertheless, in some settings sediment will eventually render the storage capacity of even a large dam inoperable. Steps will then need to be taken to restore the system to a state of nonregulated flows, similar to a run-of-river project. The main barriers to improving environmental flows by decommissioning, include: Land use change: Where
land-use in downstream flood plains or around the reservoir has adjusted
to the presence of the dam and altered stream flows. For example, there
may be local opposition to changes in reservoir water levels, or full
draining where recreational uses, tourist and other facilities have been
developed. Downstream, there may be encroachment and land use in the flood
plain, where retreat or removal is either politically unacceptable, or
too costly. This 7.5m high, 280m long dam was built in 1837 for a water mill. Later it was converted to hydropower generation. In 1997, it became the first dam in US history to have its license renewal refused. The Federal Energy Regulatory Commission (FERC) determined that the power it produced fell short of justifying the adverse environmental impacts. Funds for the dam removal and the associated fisheries restoration programmes were provided by a coalition of upstream dam owners, and no public funds were used. The decommissioning work included:
Availability and cost of replacement services: Where the cost of replacing the services provided by the existing dam are high (i.e. water supply, flood control, navigation, irrigation, recreation), or where there is no feasible alternative. Downstream sediment releases: Where agriculture pesticide, toxic industrial pollutions, heavy metals from upstream mining operations etc, have accumulated in the reservoir, and their release would threaten downstream human water use activities or ecological values.
WWF Poland prepared an options assessment study that recommended decommissioning the existing Wloclawek Dam on the mid-reach of the Vistula River in Poland. This assessment was prepared as counter-proposal to build a dam immediately downstream to address a dam safety issue with the existing Wloclawek Dam. The WWF purpose was also to advance river restoration. The Wloclawek Dam is in two parts: an earth dam, on the right side of the river, and a concrete dam with gates, powerhouse and navigation locks on the left side. The study identified a procedure of:
3.4.3 Processes to engage stakeholders Some countries have regulatory processes to assess existing dams, and to decide whether retrofit, renewal, upgrade or decommissioning is appropriate. Others do not. In the United States, assessments have largely developed around processes for license renewal of existing dams. In Europe, decommissioning has been mainly linked to safety reviews and wider changes in flood management practice. Decommissioning is one option in the context of European Union directives such as the EU Water Framework Directive. The generic process for decommissioning would have some of the following stages: Stage 1. Feasibility Study and Impact Assessment
Stage 2. Public debate on options
Stage 3. Detailed design and approval of selected option
Stage 4. Construction, removal and monitoring
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Chapter 3 Modifying Water Infrastructure
3.1
Infrastructure impacts and options
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copyright 2004 IUCN - The World Conservation Union |
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