What Is A Dam? A dam is a structure, often quite large, built across a river to retain its flow of water in a reservoir for various purposes, most commonly hydropower. In the U.S. there are over 90,000 dams over 6 feet tall, according to American Rivers. In 2015 half of Earth’s major rivers contained around 57,000 large dams, according to International Rivers. Dams are complicated. This blog presents a look at some of the benefits, consequences and impacts of dams, along with NWNL photographs of North American and African dams in our case-study watersheds.
Danger sign at the Waneta Dam in the Columbia River Basin (2007)
Atchafalaya Old River Low Sill Control Structure, Louisiana (2011)
The slowing or diversion of river flows caused by dams – and related “control structures” – can have severe environmental impacts. Many species that reside in rivers rely on a steady flow for migration, spawning and healthy habitats. Altered river flows can disorient migrating fish and disrupt reproduction cycles needing natural seasonal flows.
Aerial views of Chief Joseph Dam in the Columbia River Basin (2007)
The introduction of a dam into a river creates a reservoir by halting a river’s flow. This can severely impact the quality of water. Still water can cause water temperatures to increase. Resulting abnormal temperatures can negatively affect species; cause algae blooms; and decrease oxygen levels.
Juvenile fish bypass at the McNary Dam in the Columbia River Basin (2007)
Aerial view of the construction site of Gibe III Dam in the Omo River (2007)
Bryan Jones, featured in Patagonia’s documentary “Dam Nation,” discussed today’s situation with four aging dams on the Lower Snake River (authorized in 1945) in his 2014 NWNL Interview: “We used science then available to conquer and divide our river systems with dams. But today we can look at them and say, ‘Well-intentioned, but it didn’t really work out the way we would’ve liked it to.'” Dams that may have been beneficial at one point in history must be constantly reassessed and taken down when necessary to restore river and riparian ecosystems and species. Some compare dams to humans, since they too have a limited life span of about 70-100 years.
Small dam across the White Nile River in Uganda (2010)
Construction of the Bujagali Dam on the White Nile River in Uganda (2010)
There are well-intended reasons to build dams. In the US, the Federal Emergency Management Agency (FEMA) has listed the values of dams on their website. Those benefits include recreation, flood control, water storage, electrical generation and debris control. These benefits are explained on the FEMA website.
Danger sign at the Guntersville Dam, Tennessee River Basin (2013)
Parker Dam (a hydrodam) on the Colorado River, Southern California (2015)
Between 1998 and 2000, the World Commission on Dams (WCD) established the most comprehensive guidelines for dam building, reviewing 1,000 dams in 79 countries in two years. Their framework for decision-making is based on recognizing rights of all interested parties and assessing risks. Later, the European Union adopted this framework, stating that carbon credits from large dams can only be sold on the European market if the project complies with the WCD framework.
Many conflicts swirl around the impacts, longevity and usefulness of dams. NWNL continues to study dam benefits versus their impacts, including removal of indigenous residents in order to establish reservoirs; disruption of the downstream water rights and needs of people, species and ecosystems; and relative efficiencies of hydropower versus solar and wind. Dam-building creates consequences. Native Americans studied risks of their decisions for seven generations. After the Fukushima tsunami caused the release of radioactive material, Japanese novelist Kazumi Saeki wrote: “People have acquired a desire for technology that surpasses human comprehension. Yet the bill that has come due for that desire is all too dear.”
Sources and resources for more information:
American Rivers, How Dams Damage Rivers
International Rivers, Environmental Impacts of Dams
International Rivers, Problems with Big Dams
International Rivers, The World Commission on Dams Framework – A Brief Introduction
National Hydropower Association, Why Hydro
NWNL, Interview with Bryan L. Jones
New York Times, Kazumi Saeki, In Japan, No Time Yet for Grief
All photos © Alison M. Jones.