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I I I I I I I I I I I I I I I I I I I 26 maintenance access road which can also be utilized as a hiker- biker trail are the main items of the second construction phase. These improvements are needed to bring the drainage- way into conformance with the standards recommended by the Urban Drainage and Flood Control District. to discharge flows exceeding the normal ditch flow into the planned facilities. This insures that storm runoff flows will not be conveyed along the ditches and released at uncontrolled points. 2. Irrigation Ditches. The Welch Ditch, the Agricultural Ditch and the Rocky Mountain Ditch cross Lakewood Gulch. Overflow structures are recommended at all ditch crossings 3. Street Crossings. Kipling Street, Wadsworth and Sheridan Boulevards are the only streets crossed by Lakewood Gulch which are considered arterial streets. Urban Drainage and Flood Control District criteria recommends that such arterial roadways be passable for use by emergency vehicles during a 100-year flood. The proposed facilities at Kipling Street and Wadsworth Boulevard are sized to convey the 100- year flood in such a manner that the water depth at the street centerline will not exceed six inches. This is considered to be sufficient assurance that the streets will remain passable. Investigations showed that it would be more economical to design the Wolff Street Bridge (east of Sheridan Boulevard) in accordance with the above criteria than to improve the bridge at Sheridan Boulevard to convey the 100-year flood. During a major storm, Wolff Street could be used as a detour when Sheridan Boulevard is closed. Facilities at all other crossings are sized in accordance with their importance to handle the local traffic; that is, overtopping during a 100-year flood shall not exceed l8 inches in depth. Crossings which have no bearing on local traffic flow were exempt from the above Basis of Design Several basic design criteria were used in the development of this Master Plan, and are presented below in outline form. 1. Open Channels. All open channels consist of cross-sections as illustrated on the plans. All contain concrete, low flow channels. Channel sides are generally 4:1 slopes with natural grass cover or steeper slopes protected by tiered gab ions or concrete lining. The longitudinal channel slopes are controlled through regularly spaced drop structures. The drop structures are located in order to reduce average velocities during 100-year floods to between 7.5 and 8.0 feet per second. Maintenance access is planned along all open channels, from either public streets or roadways which will also serve as hiker-biker facilities.