At What Flow Can They Grow?

?

From May, 1995 (Update #24)

Part I

ARLINGTON, Texas - Although many studies have reported that zebra mussels can live in water flows of up to two meters per second, a recent study by two Texas researchers suggests they can tolerate water flows only about one-eighth that velocity. University of Texas-Arlington's Mike Clarke and Bob McMahon reported at the Fifth Annual Zebra Mussel Conference that zebra mussels have difficulty producing byssal threads - the protein strands that they use to attach to hard surfaces - at velocities greater than 0.27 meters per second. McMahon suspects that reports of zebra mussel attachment at higher velocities were obtained from studies of mussel colonization in water intakes, where cracks, ridges and corners produce low velocity refuges allowing mussel attachment to take place. Attached mussels, in turn, could produce additional low flow refuges, allowing a colony to develop in an otherwise inhospitable flow environment.

Part II

NORRIS, Tenn. - The zebra mussel's intolerance of high flow conditions could be used to reduce intake fouling, according to Patrick March, director of the Tennessee Valley Authority (TVA) Engineering Laboratory. March proposes retrofitting "formed suction intakes" into the rectangular forebays of existing power plants. The hydrodynamically designed structures would eliminate flow separations and create accelerating flow conditions within the intake, reducing potential mussel attachment. Distributing chemical insertion "ports" at key locations along special structures to feed molluscides or oxidizing chemicals into the laminar boundary layer, March suggested, could reduce the amount of chemicals required to eliminate mussel attachment. Such intake structures could also reduce vibration, minimize cavitation and eliminate air suction problems that develop when water levels fluctuate below design water levels, which has occurred at several TVA power plants during drought conditions. March noted that typical circulating water intake forebays for thermal power plants are rectangular and made of concrete - conditions guaranteed to produce numerous flow separations and low flow areas suitable for mussel growth. March is interested in whether other power plant operators have tried or considered retrofitting existing intakes with a similar type of intake design. The TVA engineering director believes such structures could be installed at a cost comparable to retrofitting some power plants for thermal treatment. Anyone interested in the issue is encouraged to contact March at (615) 632-1903.

ID: 199505-8.

The Zebra Mussel Update was a 4- to 8-page quarterly national newsletter published by the University of Wisconsin Sea Grant Institute from May 1990 through May 1997. The ZMU documented the spread of the zebra mussel -- an exotic nuisance mussel -- through North America's freshwater environments, especially the Great Lakes, and on efforts to control it.