Library Index » Science Encyclopedia » Surface Water: Rivers and Lakes - Characteristics Of Rivers And Lakes, The Need For Pollution Control, Assessing Water Quality, Water Quality Of The Nation's Riversand Streams

Surface Water: Rivers and Lakes - Dams—unexpected Consequences

salmon fish snake corps

The United States is second only to the Republic of China in the use of dams. Some 100,000 dams regulate America's rivers and creeks; 5,550 are more than fifty feet high. Nationwide, reservoirs created by dams encompass an area equivalent to New Hampshire and Vermont combined. Of all the rivers more than 600 miles in length in the lower forty-eight states, only the Yellowstone River still flows freely.

Being a world leader in dams was a point of pride during the golden age of dam building, a fifty-year flurry of construction that ended about 1980. Dam construction was also a way to employ many people who were out of work during the Great Depression of the 1930s and to foster national pride. Dams epitomized progress, Yankee ingenuity, and humanity's mastery of nature. After 1980 dam construction fell into disfavor. Three factors accounted for most of the decline: public resistance to the enormous costs; a growing belief that politicians were foolishly spending taxpayers' money on "pork barrel" projects, such as dams, that only benefited their local economies; and a developing public awareness of the environmental degradation that dams can cause.

Where Have All the Rivers Gone?

Dams provide a source of energy generation; flood control; drinking water; irrigation; recreation for pleasure boaters, skiers, and anglers; and locks for the passage of barges and commercial shipping vessels. However, they also alter rivers and streams, the land abutting them, the water bodies they join, and the aquatic life throughout, resulting in significant changes in the river system.

Recognizing the need to protect and maintain the aquatic environments and biological diversity of river systems, more dam operators are now required to maintain a minimum flow in the river below the dam. In addition, many dams are being retrofitted with fish ladders (a series of pools arranged like steps alongside a river or stream) and other means of access to permit fish to reach spawning areas above the dam. Fish ladders are also helpful in allowing juvenile fish to reach the river below the dam. Some states have programs that remove abandoned or obsolete dams, such as those that once served to power flour mills, or to remove other obstructions to fish passage, such as road culverts.

Snake River Dams

Correcting the environmental damage done by dams can be a costly and time-consuming undertaking. One example of a project designed to remedy damage caused by dams is the U.S. Army Corps of Engineers' project on the 1,040-mile Snake River, a major tributary of the Columbia River that runs from Yellowstone National Park in Wyoming through southern Idaho to join the Columbia River in Washington State. The goal for this ongoing project is to improve salmon and steelhead migration cycles through the dams on the Lower Snake River. Wild salmon and steelhead use the waters of the Columbia River Basin as their spawning grounds.

The U.S. Army Corps of Engineers (often referred to simply as the corps) operates nine out of the ten major federal projects in the Columbia and Snake River Basin. Of these, four dams generate hydroelectric power on the Lower Snake River. These Snake River dams are used (1) to generate 5% of the hydroelectric power for the Pacific Northwest, (2) for irrigation in the region, and (3) to enable navigation on the Snake River. Each of the dams is about 100 feet high and 2,655 to 3,791 feet wide.

Salmon stocks have declined in the Pacific Northwest during the twentieth century. In 1991 the National Marine Fisheries Service officially declared Snake River sockeye salmon an endangered species. The following year Snake River Chinook salmon were designated as a threatened species. These declarations triggered a series of actions required by law under the federal Endangered Species Act of 1973. One of the actions required was the development of a recovery plan. The Columbia River Fish Migration program grew out of this recovery plan.

According to a report by the Pacific Salmon Coordination Office of the U.S. Army Corps of Engineers (Columbia River Basin—Dams and Salmon, http://www.nwd.usace.army.mil/ps/colrvbsn.htm), there are many factors that account for the sharp decline of salmon stock in the Columbia and Snake River Basin. Among those factors are dams. The Columbia River Basin report maintains that

Dams clearly have had a significant impact, particularly those that eliminated access to fresh water habitat (preventing adult fish from returning to spawn), and those through which fish passage is provided but at reduced levels from natural conditions.

The dams impede juvenile and adult migrations to and from the ocean by their physical presence and by creating reservoirs. The reservoirs behind the dams slow water velocities, alter river temperatures, and increase predation potential.

Studies have been going on for many years to determine how best to alter the Snake River dams to reduce their negative impact on salmon and steelhead populations. All four of the dams on the Snake River have fish ladders for upriver migration of salmon returning to spawn and a bypass system for the downriver migration of juvenile salmon. As part of its Columbia River Fish Mitigation program, the corps is focusing on improving the passage of adult and juvenile salmon around these dams.

The corps has been evaluating four fish passage alternatives, the most controversial of which is breaching the dams; that is, removing the earthen portions of the dams and allowing the river to course around the remaining concrete structure. Breaching the dams would help the salmon but it would eliminate a source of hydro-electric power, water for irrigation, and a waterway for barge transport to ports 140 miles upstream. The other alternatives are to:

  • Maintain current operations
  • Increase the transportation of juvenile salmon around the dams
  • Make improvements to the dams' systems for collecting the juvenile salmon and barging or trucking them past the dams

Because changing the dams' operation can have significant environmental consequences, the corps prepared a draft environmental impact statement (EIS), which was published in February 2002. The corps' recommendation in the EIS was to move forward with the last alternative mentioned—improving the dams for the collection of juvenile salmon. However, no direct action on this plan had been taken as of May 2003, when a legal ruling in a related case led to a reconsideration of the dam-breaching alternative.

On May 7, 2003, U.S. District Judge James A. Redden ruled in a case brought against the National Marine Fisheries Service (NMFS) by seventeen conservation and fishing organizations (Ruling against NMFS BiOp Revives Dam Breaching Debate, Columbia River Inter-Tribal Fish Commission, http://www.critfc.org/text/press/20030513.html). The ruling found that the NMFS' 2000 biological opinion, upon which the corps' Columbia River Fish Mitigation program was based, fell short of the requirements of the Endangered Species Act. As a result, the corps was required to prepare a revised EIS based on a more stringent NMFS biological opinion. In March 2005, however, Judge Redden again ruled against the NMFS, Army Corps of Engineers, and Bureau of Reclamation, stating that the 2004 "Updated Proposed Action" of the three agencies did "even less to protect salmon survival" than the 2000 version (http://www.critfc.org/legal/joint_memo.pdf, March 21, 2005).

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