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<br />S\agecoach Dam was originally <br /><:- designed as an earth-rock dam in the <br />early 1970's. but was not constructed <br />for economic reasons. The expanding <br />need for irrigation water led the dis- <br />trict to evaluate this project in order <br />to develop an economic water stor- <br />age system. The developing roller- <br />compacted concrete (RCC) technol- <br />ogy provided a cost-effective project <br />with surplus water for additional <br />local needs. <br /> <br />Factors contributing to the cost <br />effectiveness of this project include <br />the following: <br />. Speed of construction (two short <br />mountain construction seasons) and <br />the subsequent reduced diversion re- <br />quirements at the narrow gorge site <br />. Design of over-the-dam service <br />and emergency spillways. The dam <br />is designed to pass the probable <br />maximum flood over the crest, in <br />contrast to a more expensive side <br />channel <br />. Decreased size of the spilling <br />basin due to a stepped spillway chute <br />. Decreased costs for a shorter <br />combined outlet works/penstock <br />. RCC construction materials <br />(sub-standard concrete aggregate) and <br />low cost forming and placement <br />techniques <br /> <br />Stagecoach Dam utilizes a stepped <br />spillway design to reduce stilling basin <br />size and associated project costs. A <br />1:24 scale model of the spillway was <br />constructed, operated and analyzed in <br />. order to determine design require- <br />ments. The model included one-, <br />two-, and four-foot step heights. Con- <br />ditions studied by use of the model <br />included: <br /> <br />. Step size versus energy dissipa- <br />tion and flow conveyance <br />. Crest performance <br /> <br /> <br /> <br />DAM CREST <br /> <br />LGALLERY j <br />lJiRCC <br /> <br /> <br />The dam across the Yampa River <br />near Steamboat Springs, Colorado <br />provides a large reservoir for munici- <br />pal, industrial, agricultural and recrea- <br />tional use. It also includes a 1:t MW <br />hydropower plant. <br /> <br />Dam height: 145 feet <br />Dam crest: 7210 elevation <br />340 feet long <br />24 feet wide <br />Upstream face: vertical <br />Downstream face: 0.8:1 stepped <br />Reservoir: 34,000 acre-feet <br /> <br /> <br />FOUNDATION <br /> <br />DAM PROFILE <br /> <br />The dam design used conventional <br />gravity dam design concepts, modified <br />for RCC construction techniques. <br />The RCC technique involved special <br />construction for the gallery, diversion, . <br />penstock, intake tower, drain systems <br />and dam mass. Exterior faces were de- <br />signed consistent with local weather. '. <br />conditions and appearance. The hy~:':~ <br />dropower plant was added to fully .~::s I <br />. ..l <br />utilize the water resource available a~: <ii <br />h . .~ <br />t e site. '_ ~"'~ <br />. ....":.~ <br />.-"'~~ <br />.-~. . <br />.. -li~ <br /> <br />\.RCC") <br /> <br />SPILLWAY CREST <br />