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FDP for Stroh Pit Item 6. <br /> March 21, 2023 <br /> 105621 4,845.50 4845.5 0.00 <br /> 104990 4,845.13 4845.13 0.00 <br /> 104063 4,844.13 4844.13 0.00 <br /> 103233 4,842.12 4842.12 0.00 <br /> 102588 4,840.41 4840.41 0.00 <br /> 101840 4,839.07 4839.07 0.00 <br /> 101140 4,838.05 4838.05 0.00 <br /> 100479 4,837.18 4837.18 0.00 <br /> 98201 4,834.98 4834.98 0.00 <br /> From the table above, it is shown that there are no rises in WSELs to within 0.00 ft for the 1-PAC storm <br /> event for all cross sections. The initial no-rise model considered only the obstructions, resulting in slight <br /> increases in the WSELs.To ensure that the no-rise condition is achieved,the no-rise model was revised <br /> by modifying the ground surface to incorporate lowering in elevation beneath the obstructions. The <br /> conveyor head section will be mounted on concrete spread footers and the tail pulley section will be <br /> anchored onto precast concrete blocks (see Attachment I for conveyor belt details)to hold the conveyor <br /> belt in place during flood events. An electronic copy of the hydraulic models is included in Attachment <br /> K. <br /> The area that will be disturbed by the obstructions of the conveyor belt, cut along the conveyor, <br /> excavation of trenches, and placement of the underdrain pipes can be seen in the disturbance limits <br /> map in Attachment C. The certified construction plans for the conveyor belt along with cut, underdrains, <br /> and berm can be seen in Attachment E. The property ownership documentation is included as <br /> Attachment H. <br /> Underdrain Outfall Riprap & Scour Analysis <br /> There are two underdrain outfalls, one upstream at cross section 104063 and the other at the <br /> downstream cross section 100479. They will outfall to the right bank of BTR with the end of the pipes <br /> being flush with the bank, which will be restored to its pre-project configuration. Both outfalls will be <br /> located at straight sections of the channel. Scour calculation was performed in HEC-RAS model to <br /> determine the maximum depth of scour that may occur at the outfalls. The size of riprap protection for <br /> the pipe outfalls were also determined using HEC-RAS model. At both outfalls, the riprap size was <br /> determined to be d5o=6 inches with riprap thickness of 12 inches. The riprap aprons will extend <br /> minimum 3 feet below the channel thalweg elevation to protect against the scour at the channel bottom <br /> since the scour depths were calculated to be approximately 1.7 feet. Please see Attachment J for scour <br /> and riprap design calculations. <br /> Conclusions <br /> In conclusion, the proposed construction activities for the Stroh Pit site that are located within the Big <br /> Thompson River floodplain will not cause rise in the 1-PAC flood WSELs. The "No-Rise" certification is <br /> included in Attachment F and the certification of"No Adverse Impact' is included in Attachment G. Due <br /> to no rise and the conveyor belt being temporary, we are requesting that the FDP for the Stroh Pit site <br /> be approved. If you have any questions or concerns with the proposed activities and their documentation, <br /> please feel free to contact me at your convenience. <br /> Galloway&Company, Inc. Page 2 of 3 <br /> 353 <br />