The Good and Bad About Dams
The U.S. Army Corps of Engineers (USACE) regulates work in the nation’s wetlands and waters, with a goal of protecting the aquatic environment, promoting responsible development, and working to ensure no net loss of wetlands while issuing about 90,000 construction permits a year 1. About a decade ago, a Suffield organization, whose property borders Muddy Brook, used a creative solution to circumvent the water-controlling regulations of the USACE. This organization wanted to dam up the brook to create a pond for irrigating its land, but did not want to undergo the USACE approval process. So instead, they imported and released a family of beavers. The plan worked beautifully; the beavers built a dam in the brook creating the desired irrigation pond, and pumping activity began. Curious neighbors, who had watched and wondered about the construction of the pumping and irrigation system, enjoyed watching the beaver activity as the plan came to fruition. Unfortunately, after five years, the beavers moved on to another spot in the brook, and the organization had to resort to other irrigation plans.
A typical beaver dam
For a very long time, humans and other animals have been piling all sorts of materials into the path of flowing water in order to control that precious resource. Whether the damming material is dirt, wood, stone, or concrete, this behavior has certainly had a major impact on the natural water cycle and river-based ecosystems. Many of those impacts have been positive. Dams have been used for hydroelectric power generation, flood control, and to create reservoirs for drinking water, irrigation, recreation, and transportation.3 Often times, dams are multi-purpose. For example, Hoover Dam4 on the Arizona/Nevada border is a major power station in the Southwest. It controls flood water flows of the Colorado River, and creates Lake Mead, the largest reservoir in the United States (247 square miles and 550 miles of shoreline). This 112 mile long reservoir provides multiple irrigation and recreation opportunities for residents and visitors to the area.
The United States has about 75,000 dams blocking 600,000 miles of what was free-flowing water on 17% of the nation’s rivers.5 While these dams are providing much positive benefit to the human population, there are many significant negative impacts, as well.
When dams are used to create large reservoirs, there are usually small towns buried under the rising water. This creates major upheaval for the residents of those towns, who need to find a new place to live. Famous examples of buried towns include St. Thomas, Nevada (under Hoover Dam’s Lake Mead), Enfield, Massachusetts (under Boston’s Quabbin Reservoir), and Barkhamsted Hollow, Connecticut (under Hartford’s Barkhamsted Reservoir).
Dams hinder the downstream flow of water, and water removed from Reservoirs limits the available water for downstream ecosystems. The use of Colorado River water, made easier by reservoir impoundment, regularly prevents the river from flowing all the way to its mouth at the Gulf of California.
Dams severely impact the ability of migratory fish, such as salmon, to swim upstream for their annual reproductive activities. Fish ladders and elevators are sometimes used to help fish continue their upstream journeys around the dammed barriers, but this adds another great stress to an already very stressful journey.
Dams also have impacted river transportation; human engineering has been able to construct canals and locks to circumvent some of those barriers, but this adds greatly to the cost of building and maintaining the infrastructure.
Finally, dams are a part of the major infrastructure problem that exists in the United States and other countries. The power of water puts tremendous strain on constructed dams. Even though quality engineering has allowed most dams to survive and function effectively for many years, the possibility of failure over time produces great risks for downstream residents.6
While dams provide important advantages for human society, there has been quite a bit of controversy and worry about their usage and their long-term impacts. As we continue forward with a more environmental focus, the future of dams will be under close scrutiny.