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I I I I I I I I I I I I I I I I I I I T E C H N I C A L M E M 0 RAN DUM TO: Mr. Nick Ioannides, P.E.; Colorado Water Conservation Board FR(X.1: Wright Water Engineers, Inc. ~~ DATE: April 24, 1986 SUBJECT: PROTOTYPE ANALYSIS, BROWN DITCH WEIRS The Work Plan dated March 12, 1986 included Prototype Analysis under Item 6 to provide physical flow data for use in design computations and boat chute layout. The intent was to select one existing boat chute for inten- sive analysis. Wright Water Engineers, after analyzing numerous boat chutes in the field, selected the lower Oxford Avenue drop structure of the U.S. Army Corps of Engineers for primary study. A detailed field instrument survey was performed on the subject U.S.A.C.E. drop. Wright Water Engineers purchased and had delivered a load of derrick stone to assist in the analysis and rehabilitation of the boat chute. Work was scheduled three times, but cancelled each time after conferring with the U.S.A.C.E. at Chatfield Reservoir. Nevertheless, site visits were made to the lower Oxford Avenue drop to collect hydraulic data and to review the drop and chute hydraulics under a range of flows. This data has been uti- lized fully in our work to date. Based on the Oxford Avenue investigations, conclusions reached are as fol- lows: 1. The lower boat chute at Oxford Avenue was not constructed properly. See the attached as-built drawing>. a. The middle drop, at nearly three feet, is excessive in height. It was pl anned to be tv,() feet. b. The chute receives an excessive proportional anount of the river flow. At 300 cfs in the river, the boat chute is estimated to have carried approximately 200 to 250 cfs. c. The boat chute is too narrow. Deflectors would be desirable to avoid abrupt waves. d. Rocks are not \'o\:ll-placed at the tail-end of the chute. 2. Field inspection control of boat chutes is necessary, along with fo 11 ow-up adj ustments. . U Z - . I II II Z i!i z II IE ~ ~ l- I !2 IE