Dams and Impounded Rivers - River Dynamics and Integrated River Management - page 429

advantage that the mechanics of the failure, from initiation to breach can be modeled; the details of the
dam and its foundation and the ability to intervene to prevent breaching. However, sometimes there is
little objective basis for estimation of the conditional probabilities within the event tree, and, therefore, it
may be necessary to relate back to historic performance data as a “credibility check” on the answers.
7.3.2 Dam Removal
Dams have some negative impacts for while they provide power, water supply, navigation, and flood
control capacity, they also obstruct river flows, alter nutrient cycles, block fish migration, and disrupt
temperature regimes and dissolved oxygen concentrations favorable to aquatic life. Prime habitat is
commonly lost, and exotic fish species are introduced. Dams also undermine the rights and livelihoods of
affected communities. Increased international recognition of the high environmental and social costs of
dams, along with numerous river restoration successes, are inspiring dam removal campaigns worldwide.
Numerous dams are now slated or proposed for removal. Many have simply outlived their purpose or
sit abandoned, posing a danger to public safety. Other dams continue to operate, though with significant
environmental and social consequences. Over a dam's lifespan, costs borne by damaged ecosystems and
communities may outweigh other project benefits. With dam removal already outpacing dam construction
in the U.S., decommissioning has significant implications for global river management.
7.3.2.1 Dam Removal in the U.S.
The American Society of Civil Engineers published the Guidelines for Retirement of Dams and Hydroelectric
Facilities in 1997 (TCGRD, 1997). About 500 dams have been removed in the U.S., and most of them are
less than 12-m high (Melching, 2006). The dam removal campaign is accelerating. Only 138 dams were
removed before 1990; 177 dams were removed in the period from 1990 to 1999; and 185 dams have
been removed in the period from 2000 to 2006. The dam removal campaign focuses on the removal of
dams that do not make sense. In other words, these dams no longer serve their intended purpose or the
dam's costs outweigh its benefits. Dam removal also involves those in a state of disrepair with no one to
claiming ownership. Most of these dams were built decades ago and many have deteriorated due to age,
erosion, damage, and for poor design.
Reasons for dam removal are : 1) ageing; 2) ecological restoration; 3) too expensive to repair and
operate; and 4) nobody claims the ownership. In the U.S. there are more than 75,000 dams more than 2 m
high, which obstruct 950,000 km of waterways. Firstly, safety is one of the reasons for dam decommission
activities. About 1,800 dams in the U.S. are officially deemed unsafe. By 2020, 85% of all government
owned US dams will be at least 50 years old, the typical design lifespan. Supporters of dam removal are
calling attention to a serious lack of funding for dam safety programs.
Secondly, dam removal is an emerging option in relicensing proceedings, in which private hydropower
dam owners seek to renew 30- to 50-year operation agreements with the Federal Energy Regulatory
Commission (FERC). More than 500 FERC licenses will expire in the next decade. The dam relicensing
process is forcing dam owners, government decision makers, river advocates, and affected communities
to re-evaluate the costs and benefits of dams, especially in light of mandates to protect endangered species,
recognize tribal fishing rights, and give "equal consideration" to fisheries, recreation, and environmental
quality. In a growing number of cases, removal of unsafe or obsolete dams represents the best river
management option. For instance, removal costs of 70 small dams in Wisconsin were found to be an
average of 2-5 times less than estimated repair costs. The following are a few examples:
On the Baraboo River, Wisconsin, the cost of removing the 3-m high Oak Street Dam was $30,000,
compared to repair estimates of $300,000;
In Maine, the removal cost for the 8-m high Edwards Dam was roughly one third of the $9 million
price tag of upgrading fish ladders.