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I I I I I I I I I I I I I I II I I I I I Mr. Nick Ioannides Apri 1 24, 1986 Page 2 3. The Oxford Avenue boat chute can be rehabi 1 itated without a major ef- fort using the rock delivered to the site by Wright Water Engineers, concrete grout, and careful on-site hydraul ic engineering control. Due to the high-flow releases from Chatfield Reservoir and as a result of our discussions with the U.S.A.C.E., Wright Water Engineers selected an al- ternative location for its Prototype Analysis work. This alternative location was selected because stream flow was adequately controlled, and the location provided for a study of the important "drop chute" configuration with field analysis of the action of deflectors which could be studied in detail under a range of flows of up to 180 cfs. The alternative site is in Boulder, Colorado, Street on the University of Colorado campus. described below: on Boul der Creek at 19th The Prototype An a 1 ys i s is Prototype Alternative Location and General Information: Boulder Creek flows in a generally easterly direction from the mouth of Boulder Canyon through the City of Boulder. Nineteenth Street dead-ends at a small foot bridge over Boulder Creek approximately 1.5 miles east of the canyon mouth, located within the University of Colorado campus. At this loc~tion, a large, concrete-encased sewer line crosses the creek. The con- crete encasement protrudes approximately four feet into the channel section. Over time, the flow of the creek over the face of the encasement scoured a deep (four- to five-foot) hole at the downstream base of the crossing (see Figure 1). This created a dangerous "hydraulic" for creek users, particu- larly inner-tubers, who v,()uld go over the concrete face and might be trapped in the "hole" at the bottom. The action of the water was also undermining the concrete encasement, which v,()uld lead to eventual failure of the sewer crossing. (See Photo 1.) Prototype Description Due to several simil ar design problems and parameters this drop has to the proposed chutes on the South Pl atte River, this location was picked for pro- totype study for the Columbine Valley \'o\:irs. The v,()rk was pl anned and coor- dinated with the City of Boulder and scheduled to fit in with the City con- tractor's pl ans. The design team met several times to discuss the design to be tested. A ch ute wi th "offset defl ectors" was selected. The fo 11 owi ng work was then accompl i shed under the guidance of the design team members. 1. The deep scour hole at the base of the sewer encasement was fi 11 ed with large, solid stone (two to three feet in diameter). Enough stone was delivered to the site to fill the hole, to have a sloping face from the top of the encasement, and to construct deflectors along the edges of the channel. .