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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 />utilize a detention facility as outlined in Alternative Two. Thus, there is no increased flood <br />hazard to County residents higher in the Coal Creek basin. The potential for increased <br />flooding hazard was a shortcoming of Alternative Two, and is solved with the design <br />concepts presented in the Preferred Alternative Five. The overall concept for the Preferred <br />alternative is shown on Exhibit Four. <br /> <br />To maintain the Boxelder Creek water surface elevation at its current level some right-or- <br />way or easements will be needed. Thus, the project estimated cost shows a line item for <br />the purchase of right- or-way. The town is currently negotiating land agreements for <br />rights-of-way and easements. The town will use the present land value as a portion of the <br />in-kind matching for the overall project cost. <br /> <br />The conveyance system from County Road 66 to Boxelder Creek will be an open channel <br />with box culverts used at road and railbed crossings. The conveyance channel will <br />terminate at Boxelder Creek in the northern part of Town. Channel improvements will be <br />made to Boxelder Creek from the confluence with the conveyance channel south for a <br />distance of approximately three miles to the Boxelder bridge at Interstate-25. This <br />southern terminus was chosen because the confluence of Coal Creek and Boxelder Creek <br />are above the bridge. <br /> <br />The Boxelder Creek channel improvements are increasing the cross section to convey the <br />modified flow, protecting the channel and bridges from erosion, improvements to existing <br />bridges to increase hydraulic capacity and constructing a new bridge at County Road 62. <br />Today, the County Road 62 crossing consists of a 30-inch metal culvert with an AArizona <br />Crossing, a road sag curve that dips into the channel. No formal bridge exists at this <br />location. Furthermore, it is believed that the cost of the bridge will be shared with Larimer <br />County. <br /> <br />Hydraulic computer modeling demonstrates that the changes in flow regime slightly <br />increase the flow at the Coal Creek/Boxelder Creek confluence. This increase in flow is <br />due to planned channel improvements along Boxelder Creek. The final design calls for the <br />water surface to be maintained at or below the elevations shown in the most recent FEMA <br />Flood Insurance Study for Boxelder Creek. Maintaining the water surface will continue <br />the hydraulic conditions upstream and down stream of the project reach. During the <br />design period a Conditional Letter of Map Revision will be completed for FEMA review. <br /> <br />DISCUSSION OF PREFERRED ALTERNATIVE <br /> <br />The preferred alternative is: Alternative Five - Undetained Diversion to Boxelder Creek. This <br />decision is based on a variety of considerations including: technical feasibility, ability to pay, <br />benefit/cost analysis and non-quantifiable benefits. It is believed that the Undetained Diversion to <br />Boxelder Creek makes it the best option because it maximizes the benefits to the overall <br />community and minimally impacts to Larimer County residents outside the proposed project. <br /> <br />Benefits that accrue to the overall project are the inclusion of a bike trail; development of open <br /> <br />10 <br />