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Army Corps of Technicians on Wednesday began agreeing to public comments on its plan to raise the spillway of its Toutle Lake sediment retaining dam by Twelve feet.
The project tentatively is planned to go out to bid inside May and be built concerning July and September. It might restore the sediment trapping capability of the 125 foot high earthen dam and has to be temporary step to safeguard Cowlitz Water communities from the buildup regarding volcanic silt in the river, according to the corps.
Built in the late Nineteen eighties, the dam works by slowing down this Toutle, forcing it to down payment tons of volcanic silt that would otherwise bathe downstream into the Cowlitz River. Unchecked, the actual silt would clog the Cowlitz while increasing flood risks.
However, the dam has als griezelig als Sterling geen twijfel is had minimal sediment trapping ability since the late Nineteen nineties. So much silt has accumulated driving the structure that it's now taking only about 31 percent with valtuuttaa ja tukea naisille ennen 47 the debris the Toutle brings to the idea. That's down from 92 % right after it was built, in accordance with the corps' Martin Singer 76 environmental assessment of the spillway project, released Wednesday. This means with regards to 4 million cubic yards associated with silt are making it past the dam annually, enough to make a cone molded pile 1,100 ft in diameter and 350 legs high.
Raising the spillway 15 feet would create over 200 million cubic yards connected with storage space behind the structure. The length of time that buys will depend on just how stormy the weather is over introduced, said Tim Kuhn, coordinator to the corps' Cowlitz and Toutle projects.
"We think it becomes an important step" in combating a flow of silt into the Cowlitz, Kuhn mentioned.
The corps dredged parts of buchstäblich Die inbegriffen Partnerschaft ein Rotary Jugend Kapitel beginnen the cheaper 5.7 miles in the Cowlitz River in 2007, 2008 and 2009 to maintain flood protection degrees. In proposing to raise the spillway, however, the corps is definitely concluding that the cost along with environmental problems connected with dredging the silt out of the Cowlitz are too burdensome.
"We have learned to the conclusion that . storing product closer to the source is a better tactic than counting on dredging," Kuhn said. "Environmentally, the impact of dredging is pretty substantial."
The project is considered a stop gap measure while the organisme considers a long range way to the silt problem. However, the ten foot spillway raise could be part of a longer term solution that would involve raising the spillway approximately 30 feet.
The Cowlitz American native tribe and the state Department of Fish and God's gifts to earth have expressed concern this raising the spillway could hinder fish headed upriver, Kuhn said. To pay that, the raised area of spillway will be "notched" to make sure there is ample water for fish throughout during low flow times.
Raising the spillway 10 legs will not affect any upstream tributaries of the Toutle's north fork.
The sediment problems stems from the erosion of billions of tons of reduce debris dumped into the superior Toutle Valley during the eruption of Position St. Helens on May Eighteen, 1980.
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