A sheet of steel breaks the surface beside a Missouri River powerhouse looking wrong.<\/p>\n
It should be bare metal.<\/p>\n
Instead it is furred, gray brown and lumpy, as if it grew a coat underwater.<\/p>\n
That coat is built by a living creature<\/strong>, and it weighs about as much as five pickup trucks.<\/p>\n Crews at the same South Dakota dam have been scraping it off for roughly a decade.<\/p>\n The weight comes from the zebra mussel<\/strong>, a freshwater shellfish native to Eurasia that reached American waters decades ago in the ballast water of ocean going ships. A single one is harmless and barely bigger than a thumbnail. The trouble is the way it attaches, gluing itself down with tough protein fibers<\/strong> called byssal threads that hold fast to concrete, pipe and steel.<\/p>\n Layer those animals over every submerged surface of a gate and the arithmetic turns strange. A clean intake gate at Gavins Point Dam near Yankton weighs about 88,000 pounds. Three gates pulled for cleaning averaged roughly 113,000 pounds before anyone touched them, an extra 25,000 pounds<\/strong> apiece of mussels and debris.<\/p>\n None of that buildup is visible from the crest road. It forms in the dark, underwater, on hardware that spends its entire working life submerged.<\/p>\n Gavins Point is the most downstream of the six mainstem Missouri River dams, and it is unusual among them. Most of the river’s plants run for peaking or semi peaking power, while this one<\/a> runs as baseload, generating continuously.<\/p>\n Its three generators supply enough electricity to meet the annual needs of about<\/strong> 68,000 homes. That steady output means a continuous pull of river water through intake structures and through the smaller raw water lines that cool the equipment inside, and mussels colonize both.<\/p>\n Eric Johnson, the dam’s maintenance and operations manager and assistant powerplant superintendent, told Dakota News Now that the species is “the biggest problem we have here at the powerhouse, and has been for 10 years.” He described clogged raw water systems producing unexpected shutdowns<\/strong> and lost generation, plus the man hours needed to clear them out.<\/p>\n There are nine intake gates at Gavins Point, and the Army Corps of Engineers’ Omaha District cleans three of them each year, so every gate comes out roughly once every three years. In the most recent round, carried out over three days in early August, crews removed more than 75,000 pounds<\/a> of zebra mussels from the three gates combined.<\/p>\n That is not a one time event. It is a maintenance cycle<\/strong> the dam now plans its calendar around, the same way it plans around spring runoff or ice.<\/p>\n Stripping attached mussels off the gate structures is slow, physical work. The Corps has said its maintenance time on the intake gates has more than doubled<\/strong> in man hours since the invasion began, and left alone, the buildup compounds year over year, adding more weight, more debris<\/strong> and more wear on the chains and mechanisms that raise the gates.<\/p>\n Zebra mussels turned up at Gavins Point about a decade ago, in the reservoir behind the dam, Lewis and Clark Lake. They are now established in reservoirs<\/strong> and waterways across the region, affecting cooling systems, water treatment plants and other water infrastructure well beyond this one powerhouse.<\/p>\n Once a population takes hold, removing it from an entire river system is not realistic. The dam fights it locally instead, with an ultraviolet treatment system<\/strong> and a molluscicide drip system that limit how many larvae settle and grow inside the plant’s piping and coolers.<\/p>\n The ecological cost runs past the hardware. Zebra mussels filter large volumes of water and strip out the plankton that native fish and native freshwater mussels eat, and they settle directly onto native mussels, much as a mechanical failure<\/a> elsewhere can ripple far past the equipment where it starts. A dam built to generate clean electricity<\/a> has become an unplanned gauge of how far the invasion reaches.<\/p>\n The story at Gavins Point is less about failure than adaptation. Crews have turned an infestation into a budgeted, scheduled task<\/strong>, hauling tons of shellfish off steel every summer so the turbines keep turning.<\/p>\n Research continues into better ways to kill the mollusks and keep them off the gates in the first place. The Corps keeps asking boaters to clean livewells, hulls<\/strong> and gear before moving between reservoirs, because that is how the animals travel.<\/p>\n Other waterways face their own mismatches between built infrastructure and the creatures living alongside it, from a turbine built to let eels pass safely through to a project meant to shield turtle habitat from development. At Gavins Point the mismatch is measured on a scale, in tons, three gates at a time.<\/p>\n For now the dam keeps lifting its gates, and the water keeps sending them back encrusted, a standing arrangement between<\/strong> 1950s concrete and a shellfish the size of a thumbnail.<\/p>\n","protected":false},"excerpt":{"rendered":" A sheet of steel breaks the surface beside a Missouri River powerhouse looking wrong. It should be bare metal. Instead it is furred, gray brown and lumpy, as if it grew a coat underwater. That coat is built by a living creature, and it weighs about as much as five pickup trucks. Crews at the … Read more<\/a><\/p>\n","protected":false},"author":28,"featured_media":45341,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"rank_math_focus_keyword":"steel intake gates","rank_math_title":"Steel intake gates at a South Dakota hydropower dam come out of the water about 25,000 pounds heavier than they went in, and crews scrape three of them clean every single year","rank_math_description":"Intake gates at a South Dakota hydropower dam gain about 25,000 pounds of zebra mussels a year, and crews now scrape three gates clean annually to keep th","footnotes":""},"categories":[8],"tags":[],"class_list":["post-45336","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-energy"],"_links":{"self":[{"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/posts\/45336","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/users\/28"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/comments?post=45336"}],"version-history":[{"count":1,"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/posts\/45336\/revisions"}],"predecessor-version":[{"id":45342,"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/posts\/45336\/revisions\/45342"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/media\/45341"}],"wp:attachment":[{"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/media?parent=45336"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/categories?post=45336"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ecoportal.net\/en\/wp-json\/wp\/v2\/tags?post=45336"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}A fingernail sized shellfish cements itself to steel and never lets go<\/h2>\n
A nonstop powerhouse meets a decade old problem<\/h2>\n
Three gates get scraped clean on a yearly rotation<\/h2>\n
Ten years of spread since mussels reached Lewis and Clark Lake<\/h2>\n
What three scraped gates a year reveal about the river<\/h2>\n