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<br />These are sections 14.4, IS, 15,8, 16,8, and 17,2, These sections were grouped together in the existing <br /> <br /> <br />. analysis since the floodwaters had combined into one flow path, <br /> <br />Section 17,9 will be the first cross-section that will include improvements to the channel. An existing <br />siphon for the Lower Boulder Ditch limits the proposed channel to about an 80 foot bottom width, 3: I <br />sideslopes, and a ISO foot top width, The improved channel will generally follow the existing normal flow <br />channel. The existing normal flow channel will be located within the bottom width of the channel. The <br />elevation of the invert of the channel will not be changed, so that the siphon will not be affected, A levee <br />will also start at this station along the west bank of the channel. The levee will prevent the 100-year storm <br />water flow from entering the Town along the shallow channel sections, The levee will be built with a <br />minimum of 3-feet of freeboard, Riprap with a mean diameter of 9-inches will be placed along the west bank <br />of the channel to protect the levee from erosion, The rip rap will extend from the toe of slope to I. 0 feet <br />above the 100-year water surface elevation, A stormsewer outfall with flapgate will be constructed at Evans <br />Street to allow interior town drainage to enter the channel. <br /> <br />Sections 18,5 and 18,6 are a continuation of the full channel section and levee, <br /> <br />. <br /> <br />Section 19,0 is the effective channel downstream of a new low flow crossing, <br /> <br />Section 19,1 is the new low flow crossing structure. <br /> <br />Section 19,2 is the full channel section upstream of the new low flow crossing, An existing 150 foot <br />top width channel was built prior to 1980, The channel is presently overgrown with small trees and shrubs. <br />The bottom of the channel is also not uniform and includes a number of depressions and mounds, The <br />improvements will include widening the channel by excavating the east bank and removing the trees and <br />shrubs, The owner of a property east of the Town installed two (2), 9 foot diameter equivalent corrugated <br />metal culverts in Coal Creek to access his property located approximately 350 feet downstream of Section <br />19,0, These culverts were installed after the FIRM mapping was approved in 1982, In order to maintain <br />access to the property a new three cell precast low flow crossing will be constructed to replace the culverts. <br />Each cell of the low flow crossing will have a 6 foot high by 30 foot wide opening for a total area of 540 <br />square feet. Flows above 3,000 cfs will overtop the low flow crossing, Riprap protection will be provided <br />to limIt the erOSiOn damage during large storm events, <br /> <br />. <br /> <br />5 <br />