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nedrly its existing condition as possible while making it serve the multi-purpose function of a flood detention facility and a rccreational facility. WEIR GULCH THROUGH DENVER limited right-of-way available tor the existing man-madc channel, and the street profiles surrounding the channels. After detailed discussions with the City of Lakewood, the criteria was established of designing street crossing for a minimum of a 10 year frequency, making every reasonable effort to remove additional runoff from street surfaces so that it will ~ot accumulate on Mississippi Avenue or Garrison Street, constructing a facility capable of separating accumulated flows above Agricultural Ditch from the Agricultural Ditch proper, and to provide an acceptable outflow point for spills over the Main Reservoir Spillway. The general approach to Weir Gulch through Denver consists of installing 10 year street crossings and channels with capacity limited by existing development along the right-of-way. Wherever oossible the channel should be an open grass lined channel with 3:1 side slopes. In areas where the right-of-way is not sufficient, the side slopes may be increased up to 1:1 using gabion mat or reinforced concrete protection. In certain areas in industrial developments vertical side slopes may be necessary to clear existing buildings. Throughout Lakewood, in areas where flood plain ~oning is re- commended, recommended future channel improvements are indicated to assist the City and developers in planning of improvements as the areas develop. In the recommendations for improvements to weir Gulch prepared by the Urban Drainage and Flood Control Oistrict in May, 1972 it was recommended that detention be provided below Barnum Lake in the open park area to rcduce the 2S year flow to a 10 year flow or less, with the remainder of the channel to be designed for a 10 year flow or less. Based on this criteria, the detention reservoir indicated as the Federal Boulevard Detention Reservoir was des igned. Design criteria for Barnum Lake is highly influenced by legal aspects of the existing reservoir. The criteria calls for design of reservoir improvements which will insure that runoff from the 100 year storm is maintained within the historic Weir Gulch Channel. Greater storms, which might be classified in the Act of God category, would still have overflow into the 6th Avenue area. NORTH AND SOUTH WEIR GULCaES The situation surrounding both North and South Weir Gulches is extremely similar. The deep, badly eroded channels are Un- suitable for development as drainage or park facilities in their present condition. Particularly on South weir Gulch, insufficient right-of-way exists for wide shallow side slopes which might be maintained. The design approach then becomes one of raising the channel invert by use of fill until a gentle side slope may be established for maintenance purposes. Underdrains should be in- stalled along the original channel invert to prevent artificially raising the ground water tables surrounding the Channel, TABULATED DESIGN CRITERIA 1. Grasslined Channels WEIR GULCH TIIROUGH LAKEWOOD DA~ign is baSAd on maIntenance of existing park type develop- ment where ~t w~ll satisfactor~ly meet drainage requirements with minimum imprQvements. Where construction of new channels is necessary, design will generally be based on channels having shallow grasslinod side slopes and a separate low flow channel. Check darns will be used wherever feasible to maintain the channel invert within the elevation spectrum it has already established. The majority of the channels have established flow lines lying in the hlue shale bedrOck area and any attempt to relocate the invert elevations significantly would re;ult in serious maintenance problems. Drop structures ~re recommended in areas where cutting and filling of the channel is necessary for construction reasons. ~~orever feasible, the cross section and improvement characteristics should be such that they will lend themselves to multi-purpose use as park and greenbelt areas connecting larger park developments. Whenever feasible, maintenance roads shall be included in the lowQr portions of t~c channel. If a naintenance road wide enough to pass a normal vehicle cannot be installed, at least a four foot wide pedestrian and bicycle trail shall be installed to allow maintenance personnel to reach the The basic design approach through Lakewood on Weir Gulch was to flood plain zone all areas where the opportunity is still available. This approach can be implemented from Sheridan Boulevard to Mississippi Avenue with few exceptions. One exception is the section of gulch between Ohio Avenue and Harlan Avenue which is developed to the point that flood plain ~oning is not an acceptable solution. Here the normal criteria of 10 year crossings and channel with capacity limited by right- of-way constrictions was utili~ed. The area from Mississippi Avenue to ~ain Reservoir required speci- fic design criteria particular to th~t area alone. The situation is complicated by the spillway from Main Reservoir which dis- charges directly onto !I\ississippi Avenue with no channel to receive the flow, the existence of the Agricultural Ditch Co.'s Main Agricultural Ditch and Return Ditch across the Basin, the -84- -i:l5-