Numerical model study of Smithland sediment mitigation
A recently completed numerical model study of flow and sedimentation patterns downstream from the Smithland Locks and Dams indicates that downstream sediment accumulation should be manageable, says Phil Meier, assistant vice president of hydro development with American Municipal Power Inc. (AMP).
The study, completed by Alden Research Laboratory Inc. for AMP, quantified changes in flow and sedimentation patterns resulting from a change in discharge patterns after construction of a power plant. The company plans to add a 74-MW hydro facility to the structure on the Ohio River in Kentucky. The lock and dam facilities are operated by the U.S. Army Corps of Engineers.
Construction of the power plant will change the downstream discharge patterns at the dam, Meier says. Currently, for all flow less than 300,000 cubic feet per second (cfs), flow passes through 11 radial gates on the west side of the river. Once the hydro plant is built, AMP proposes that the first 50,000 cfs will pass through the turbines, with about 3,000 cfs being used to operate the locks and as leakage. The powerhouse will be located on the east side of the river.
Alden used the MIKE 21-C model developed by DHI to simulate a range of steady state flows from 18,000 to 929,000 cfs, Meier says. The two-dimensional curvilinear model was used to simulate existing and proposed conditions. The effects of the power plant were quantified using the change in bed elevation. In addition, two 100-plus-day flood hydrographs were modeled to evaluate how the tailrace accumulates and scours sediment over extended periods of time at high flow.
Results from this model show that changes in sedimentation patterns are local. The model does not show significant changes in erosion and sedimentation in the navigation channel. The model did indicate that the tailrace channel, which will be excavated through a downstream island, requires armoring to prevent it from migrating downstream. The model also indicated that, although the tailrace channel will accumulate sediment during high-flow periods when the plant is not operating, low-flow periods will scour the tailrace with minimal use of mechanical dredging.
High salmon returns predicted for Columbia River in 2010
NOAA Fisheries predicts large returns of chinook salmon to the Columbia River in 2010. The federal government agency says its prediction is based on highly favorable conditions for growth and survival of salmon that entered the ocean in the spring and summer of 2008. NOAA Fisheries has tracked 11 ocean ecosystem indicators since 1997 to determine how variability in ocean productivity affects adult salmon returns in the Pacific Northwest, says John W. Ferguson, director of the fish ecology division of NOAA Fisheries' Northwest Fisheries Science Center.
Scientists know that survival of juvenile salmon immediately after entering the Pacific Ocean varies with the state of ocean productivity. Salmon and steelhead in the Columbia River do best when the Gulf of Alaska is warm and the Oregon and Washington coastal ocean is cool, Ferguson explains. Under these conditions (known as a negative Pacific Decadal Oscillation or PDO), the flow of water coming down the coast from the North Pacific Ocean, called the California Current, is strong. This cold water contains lipid-rich zooplankton favored by juvenile salmon, Ferguson says. In addition, winds along the Washington, Oregon, and California coastline are strong and northwesterly, causing a phenomenon known as upwelling that brings nutrients up to feed the organisms that fish eat near the surface of the ocean.
To determine the PDO cycle, scientists compared conditions in the ocean against records of salmon harvests dating to the early 1900s. For most of the 20th century, the PDO occurred in about 20-year cycles. However, more recently the changes have occurred as close as four years apart, Ferguson says. During the most recent warm-water period (2002 to 2005), salmon returns declined. In 2006 and 2007, coastal ocean conditions for juvenile salmon were in transition from a warm (unproductive) state to a cool (productive) state but were improving each year.
The results of seven of the indicators NOAA Fisheries tracks are:
-- PDO: The second most negative value of the past 11 years occurred in the winter of 2007 to 2008, providing good conditions for both coho salmon and yearling chinook salmon survival;
-- Multivariate El Niño-Southern Oscillation (ENSO) Index: This index was negative through 2008, indicating warm water was not being transported northward along and into the coastal waters off Oregon and Washington. Thus, the coastal waters stayed cold and the productive source water continued to be supplied from the eastern Pacific Ocean;
-- Sea surface temperature: Winter temperatures were the coldest in 11 years, providing favorable conditions for fish survival;
-- Deep water temperature and salinity: The coldest and saltiest water in 11 years was measured in 2008, indicating nutrient-rich water was present during the entire upwelling season;
-- Coastal upwelling: Upwelling began in late March 2008 and winds were steady during much of the summer, leading to an average year for upwelling. In addition, the transition from warm-water zooplankton to cold-water zooplankton occurred in early March 2008, meaning the food chain was populated by lipid-rich northern species early in the year;
-- Copepod species biodiversity: There was moderately low biodiversity of copepod species (marine crustaceans) in 2008, again indicating that the source of the water along the coast was from the eastern Pacific Ocean; and
-- Catches of juvenile spring chinook in the ocean in June: In June 2008, trawl surveys showed the highest number of juvenile spring chinook salmon caught of the 11 years studied.
Taken together, these indicators suggest that conditions juvenile salmon from the Columbia River experienced when they entered the ocean were highly productive and favorable for successful recruitment to adulthood. This suggests that the return of chinook salmon to the Columbia River in 2010 will be large, Ferguson says.
CEATI completes study on optimum rewind timing
CEA Technologies Inc. (CEATI) announces completion of a study that details a process for determining the optimum time to replace a generator stator winding. The report on this study is titled Optimum Timing for Generator Stator Rewinds.
The stator winding of a generator is a major component in the reliability assessment of a hydroelectric plant, CEATI says. Although failures of the stator winding are infrequent, their economic effects due to repair/replacement cost and outage cost can be significant. For this reason, plant owners often decide to rewind stators after signs of moderate aging, before the winding reaches the wear-out region of the reliability curve. Thus, they are replacing a winding that is not at or near the end of its useful operating life.
The objective of the study was to develop a process that would provide a rational basis for determining the optimum time to replace a generator stator winding, CEATI says. This process includes:
-- Analysis of the causes of the gradual aging of a winding;
-- Assessment of the winding condition from inspection and tests; and
-- Assessment of the future failure probability for a specific generator, based on its winding condition.
The report identifies and describes key winding degradation mechanisms that contribute to high winding failure probabilities. CEATI then developed projected failure probability estimates from these mechanisms, using databases and assessments by specialists. When more than one failure mode is identified during a winding condition assessment, a combined failure probability must be evaluated, CEATI says. The failure probabilities can be combined using a software tool and a procedure developed as part of the study, CEATI says.
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