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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />9. Major Drainage capacity - The capacity of roadside ditches for <br />major drainage flow is restricted by the maximum flow depth <br />allowed at the street crown (see section 8). However, the <br />flow spread should not inundate the groundline of residential <br />dwellings, or public, commercial, or industrial buildings. <br /> <br />5.7 Channel Rundowns <br /> <br />A channel rundown is used to convey storm runoff from the bank or <br />side-slope of a channel to the channel invert. The purpose of the <br />structure is to minimize channel bank erosion from concentrated <br />overland flow. The design criteria for channel rundowns is as <br />follows: <br /> <br />1. Cross sections - Typical cross sections for channel rundowns <br />are presented in Figure 5-7. <br /> <br />2. Design Flow - The channel rundown shall be designed to carry <br />a minimum of the initial storm runoff, or 1 cfs, whichever is <br />greater. <br /> <br />3. Flow Depth - The maximum depth at the design flow shall be 12 <br />inches. Due to the typical profile of a channel rundown <br />beginning with a flat slope and then dropping steeply into the <br />channel, the design depth of flow shall be the computed <br />critical depth for the design flow. <br /> <br />4. Outlet Configurations - The channel rundown outlet shall enter <br />the drainageway at the trickle channel flowline. Erosion <br />protection of the opposite channel bank shall be provided by <br />a 24-inch layer of grouted Type L riprap. The width of this <br />riprap erosion protection shall be at least three times the <br />channel rundown width or pipe diameter. Riprap protection <br />shall extend up the opposite bank to the initial storm flow <br />depth in the drainageway or 2 feet, whichever is greater. <br /> <br />5.8 Maintenance and Access Easements <br /> <br />An important aspect of storm drainage facilities is continued <br />maintenance. Maintenance of storm drainage channels and structures <br />may include periodic removal of sediment and debris; repair of <br />channel erosion; and repair of inlet, outlet, and drop structures. <br />The following minimum right-of-way or easement widths, which must <br />be shown on the Final Plat, are required by the city: <br /> <br />5 - 19 <br />