FLOOD03463 - Laserfiche WebLink

Home Browse Search

. I I I' I I -14- - FINAL PLANNING CRITERIA - maintenance and where feasible, channel cross-sections should be such that they lend themselves to multi-purpose uses. Improved channels will not be self maintaining or maintenance free. Grass or soft lined channels should be wide with flat side slopes to maintain subcritical flow and acceptable velocities. Low flow channels, lined or unlined, may also be required in order to assure the nondegrading conveyance of trickle flows. Additional criteria for improved, grass lined channels include: 3. The necessary open channels, culverts and conduits through the reach from Independence to Oak. 4. Recommendation that the lOa-year flood plain or floodway between Oak Street and the proposed reservoir be publicly acquired. II The planning criteria used for the master planning of Van Bibber Creek is consistent with that outlined in the Denver Regional Council of Governments' Urban Storm Drainage Criteria Manual (USDCM) (Ref. 6). The Manual is used as a guide for major drainageway planning throughout the metropolitan area and this provides a consistency in the planning of Van Bibber Creek. Specific criteria is provided in the following paragraphs. 1. Maximum velocity of flow in improved channels during the lOa-year storm should not exceed 7.5 fps. 2. Design depths should be in the range of 4 feet for the normal channel cross-sections. Depths will be greater in backwater areas. 3. Side slopes should be flatter than 3:1 for improved grass lined channels. 4. The centerline curvature of the channel should not be less than twice the channel top width, with a 100 foot minimum. 5. Channel freeboard should be at least 1 foot for the design storm. 6. Hydraulic roughness factors should be selected in accordance with the Urban Storm Drainage Criteria Manual. I I I . I I I I .' . Drainageway Design Criteria The intent of the preliminary design is to describe workable and acceptable improvements to solve the flooding problems on Van Bibber Creek. This requires that certain criteria be followed to assure that the planning objectives are met. The criteria which has been used to measure the needs of channels and culverts and bridges is discussed below. For natural channels, the channel and overbank area should be maintained to be adequate for the lOa-year runoff. Check dams should be constructed to control surface profile slope for the initial storm runoff as well as to maintain flood velocities at or less than critical velocity. Roughness factors used for analysis must represent unmaintained channel conditions. Channels In general, all improved channels are designed to convey a specified discharge recognizing, however, the possible effects of greater discharges. Improved ch~nnels should convey flood flows efficiently and safely, should not present safety hazards even when not in use as a channel, should facilitate access for Culverts and Bridges I I Culverts are conduits which convey water through an embankment