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Location and Description of the Project <br /> The Poudre Ponds project site is located southeast of the intersection of North 35th Avenue and <br /> the Cache la Poudre River. Poudre Ponds is a slurry-wall lined, state-engineer approved water- <br /> storage reservoir that has also been developed as a recreational fishery. The site is located within <br /> the NW'/4 of Section 36,Township 6 North, Range 66 West of the Sixth Prime Meridian in Weld <br /> County, Colorado. The latitude of the center of the proposed project site is 40.448746' north and <br /> the longitude is -104.729519' west. Land uses within and adjacent to the proposed project <br /> include aggregate extraction, oil and gas production, agriculture, recreational fishing and <br /> boating, and rural residences. <br /> The proposed project site is located adjacent to and within the primary alluvial terrace of the <br /> Cache la Poudre River drainage. The overall topography of the project site is predominantly flat, <br /> though gently sloping to the east. Topography of the project site has been naturally and <br /> anthropogenically manipulated to facilitate the current land uses. These modifications have <br /> included excavations for aggregate, plowing for crops, and limited backfilling for berms, <br /> roadways, trails, and levees. <br /> Project Design and Operation <br /> The design and location of the spillway are depicted on the revised Exhibit F, Reclamation Plan <br /> Map and Spillway Detail (attached). The proposed erosion protection measures include the <br /> construction of a concrete inflow point that will be created by modifying the geometry of the <br /> existing Poudre River Trail to create a trapezoidal spillway. From the inflow point, a grouted <br /> riprap spillway will extend into the impoundment to an elevation of 4,657 feet (NAVD 88). <br /> From there, graded riprap will extend to the minimum pond elevation of 4,649 feet (NAVD 88). <br /> The spillway is being designed with a bottom width of 50 or more feet with 20:1 (H:V) side <br /> slopes. The spillway will be constructed above the ordinary high water level (OHWL) of the <br /> Cache la Poudre River in the vicinity of the spillway. <br /> The inflow point will be perpendicular to the Cache la Poudre River channel, the Poudre River <br /> Trail, and the north bank of Poudre Ponds at an existing low point prone to flooding. The <br /> parameters associated with flooding that lead to erosion (shear stress and velocity) were analyzed <br /> for a variety of design storms (2-year through 100-year) and an optimal spillway design was <br /> detennined. To confine the stability of this design, a worst-case scenario was determined to <br /> analyze the stability of the structure versus extreme velocities and shear stresses. This scenario <br /> involved treating the spillway as a trapezoidal channel and detennining the maximum capacity of <br /> the channel at the proposed slope. Using this approach, velocity and shear stress values of 16.2 <br /> ftJs and 7.3 lb./ft2 respectively were detennined. Based on the maximum permissible values of <br /> 18 ft./s and 10 lb./ft2 respectively, as detennined by the Natural Resources Conservation Service <br /> and Colorado Water Conservation Board, the proposed grouted riprap design meets the stability <br /> criteria. <br /> In operation, the structure will allow flood stage flow from the Cache la Poudre River to enter <br /> the Poudre Ponds pool at an erosion resistant location, thereby reducing the potential for erosion <br /> 2 <br />