DATASTREME WES WEEK SEVEN: 15-19 MARCH 2004

• US water use remains steady -- The USGS recently released a report entitled "Estimated Use of Water in the United States in 2000" that indicates water use across the US in 2000 remained at the same level as it had in 1990, despite population growth. [ENN] Note that the full report is available from USGS.

• Las Vegas considers a one billion dollar water pipeline -- Faced with drought and increased demand for water, the Southern Nevada Water Authority is considering spending more than one billion dollars to build a water pipeline from several rivers in the region. [US Water News Online]

• A snowstorm rating scale proposed -- Based upon a study of 70 major winter storms that affected the Northeastern States, meteorologists with the National Weather Service and the Weather Channel recently proposed a five-category Northeast Snowfall Impact Scale (NESIS) that would rate a winter storm based upon the human and economic impact that it had on the region. This new rating system considers the amount of snow, the size of the area covered and the population residing in that area. to estimate the of the storm. [USA Today]

• Extended North American droughts may be linked to North Atlantic temperatures -- After studying the century-long US drought patterns along with multi-decade variations in North Pacific and North Atlantic sea surface temperatures, scientists with the Midwestern Regional Climate Center and the US Geological Survey report that the long-lasting and widespread droughts appear to be associated with above average sea surface temperatures in the North Atlantic. [EurekAlert!]

• Global and US Hazards/Climate Extremes-- A review and analysis of the global impacts of various weather-related events, including drought, floods, and storms during the current month. [NCDC]
• Global Water News Watch -- Other water news sources can be obtained through the SAHRA Project at the University of Arizona [SAHRA Project]
• Earthweek -- Diary of the Planet [earthweek.com] Requires Adobe Acrobat Reader.

Concept of the Week: Dams and Ecological Integrity

Dams disrupt the natural seasonal fluctuations in the flow of rivers and streams with potentially serious consequences for the integrity of aquatic ecosystems. For one, dams interfere with the upstream and downstream migration of fish. Storage of water in reservoirs behind dams reduces the downstream discharge of water, sediment, and nutrients. These and other alterations of fluvial habitats threaten or endanger more than 20% of all freshwater species.

The ecological impact of dams is extensive because these structures affect so much runoff. Worldwide, almost 3000 dams have a reservoir storage capacity exceeding 25 billion gallons--a combined volume of water roughly equivalent to that in Lakes Michigan and Ontario. The more than 70,000 dams in the U.S. can store half of the annual flow of all the nation's rivers and streams.

The continuity of the global water cycle implies that disruption of river and stream flow by dams can also impact marine and lacustrine (lake) ecosystems. In the Pacific Northwest, for example, only about 5% of juvenile salmon survive passage through dams and reservoirs on the Columbia and Snake Rivers. Salmon are anadromous, that is, they spawn in freshwater streams, but spend most of their adult life in the ocean. After hatching, young salmon (smolts) swim downstream to the Pacific Ocean, where they mature and then return to the same streams to spawn. But the 56 major dams in the Columbia River watershed are formidable obstacles to salmon migration. Largely ineffective are fish ladders designed to help the salmon move upstream and other structures that guide them downstream around hydroelectric turbines. (These turbines have been likened to giant food processors for smolt attempting to swim through them.) Furthermore, smolts on their downstream passage are held up in reservoirs where they are exposed to predators, pathogens (disease-producing organisms), and water that is too warm. Atlantic salmon have a similar fate. More than 900 dams on New England and European rivers prevent most Atlantic salmon from reaching their freshwater spawning grounds. Consequently, their population has declined to less than 1% of historical levels.

Traditionally, dam operators regulate stream and river flow for flood control and to supply water for electric power generation and irrigation. But recently, in response to greater awareness of the adverse impacts of dams on aquatic ecosystems, has come a growing interest in operating dams in ways that recreate the river's natural seasonal flow pattern and habitats. For example, this type of management is employed on the Flaming Gorge Dam on the Green River in Utah to protect sensitive habitats for endangered species including chubs and squawfish. The dam operator simulates spring floods of the pre-dam era by releasing a surge of water in May that facilitates the spawning of fish.

Controlled flooding has been used on the segment of the Colorado River that flows through the Grand Canyon in an attempt to help restore landforms and aquatic habitats downstream from the Glen Canyon Dam. Before the dam first came into operation in 1956, natural floods regularly delivered sediment from the tributaries of the Colorado River. Sand and silt built sandbars and created backwaters that provided habitat for a variety of native plant and fish species such as the humpback chub and razor sucker. The humpback chub, for example, prefers the warmer and murkier waters associated with sandbars. With the dam in full operation, sand and silt was trapped in the reservoir upstream from the dam and the sandbars and backwater habitats were gradually destroyed. The number of humpback chub in the Grand Canyon declined from about 8300 in 1993 to about 2000 today and the species is close to extinction. In an attempt to restore downstream habitats, in March 1996 a huge gusher of water was released from the Glen Canyon Dam and a fresh influx of sediment built new beaches and sandbars. But these landforms and habitats disappeared within a few months. Now the U.S. Bureau of Reclamation is proposing a new flood plan based on lessons learned from the 1996 flood. The plan is to release floodwaters from the Glen Canyon Dam for a shorter period of time (2.5 days instead of the 7-day 1996 flood) and only after a sufficient buildup of sediment so that floodwaters construct sandbars and beaches rather than washing them away.

Concept of the Week: Questions

1. Alteration of aquatic habitats by dams [(is)(is not)] a reason why some fish species become threatened or endangered.
2. Anadromous species of fish spawn in [(the ocean)(freshwater rivers and streams)].

• 16 March 1889... A war between the U.S. and Germany was likely averted as a hurricane sank all three U.S. and three German warships in the harbor at Apia, Samoa. Joint U.S., German and Samoan rescue cooperation led to the Treaty of Berlin (1889) that later settled the dispute. (Accord's Weather Calendar)
• 16 March 1975... A single storm brought 119 inches of snow to Crater Lake OR establishing a state record. (The Weather Channel)
• 16 March 1987... Softball size hail caused millions of dollars damage to automobiles at Del Rio TX. Three persons were injured when hailstones crashed through a shopping mall skylight. (The National Weather Summary) (Storm Data) (The Weather Channel)
• 16 March 1989... A winter storm brought heavy snow and high winds to the southwestern U.S. Winds gusted to 60 mph at Lovelock NV, Salt Lake City UT, and Fort Carson CO. Snow fell at a rate of three inches per hour in the Lake Tahoe area of Nevada. (The National Weather Summary) (Storm Data)
• 17 March 1878...Late-winter thunderstorm produced thunder that boomed like cannon fire in Halifax, Nova Scotia. A lightning bolt entered home, hurling a young woman sitting at the family piano across the room. (The Weather Doctor)
• 17 March 1993... A natural dam formed by a landslide three years earlier collapsed because of runoff from rainfall. A wall of water, debris and mud measuring 3 feet high by 45 feet wide crossed I-15 20 miles south of Cedar City, UT. Four injuries were sustained as several vehicles were rolled or tipped over. (Accord's Weather Calendar)
• 17 March 1998...Calgary, Alberta experienced its worst March snowstorm in 113 years, measuring 13 inches of snow at the airport and from 15 to 18 inches in other parts of the city. (The Weather Doctor)
• 19 March 1964...Up to 39 inches of snow fell at Cape Whittle for Quebec's greatest one-day snow total. (The Weather Doctor)
• 20 March 2000...A large iceberg measuring approximately 170 mi by 25 mi calved off Antarctica's Ross Ice Shelf near Roosevelt Island. The iceberg was approximately 2.5 times the size of New York's Long Island. (Accord's Weather Guide Calendar)
• 21 March 1876...More than 40 inches of snow stopped traffic in Montreal, Quebec. Trains were delayed and mail carriers resorted to snowshoes. (The Weather Doctor)

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Prepared by AMS WES Central Staff and Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2004, The American Meteorological Society.