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Job No: 360100-006-01d Client LRM Page 1 7 <br /> TELEST . <br /> Task:Awchor�stevu.Cheele Computed By_:). � Date 09/o9/2i <br /> SOLUTIONS- I N C CJ R ? c:J R A T C D <br /> moms _ Checked By: W. Ni,ccoli, �4r' -09/09/21 <br /> Calculation Documentation <br /> Problem Statement: <br /> Loveland Read-Mix Concrete, Inc. (LRM) plans to mine their Dunn Pit, located outside of Milliken, <br /> Colorado, once permits are obtained. The planned mine pits all reside within the Big Thompson <br /> River 100-year floodplain. The Colorado Department of Reclamation and Mine Safety (DRMS) <br /> requires, and good practice dictates, that mine pits within the floodplain be able to safely pass <br /> floodwater through the pits with no significant damage. <br /> Objectives: <br /> 1. Determine if protective measures are needed to safely convey floodwater through the <br /> planned mine pits <br /> 2. Size inlet/outlet structures if protective measures are needed <br /> Approach: <br /> 1. Utilize the Weld County Floodplain HEC-RAS 1-D model (modified from the CHAMP model) as <br /> a starting point and develop a 2-dimensional HEC-RAS model <br /> 2. Determine flow rates, return intervals and locations in which water flows into and out of the <br /> pits <br /> 3. Examine velocities and shear-stresses induced by flooding around the pits and identify areas <br /> requiring protection to limit damage <br /> 4. For identified areas needing protection, size conveyance structures/modifications to carry <br /> floodwaters and withstand erosive forces <br /> Data and Assumptions: <br /> 1. 100-year flood flows (20,309 cfs), considering lower flows as cells overtop prior to full <br /> inundation <br /> 2. Geometry— 2015 and 2018 digital elevation models based on LiDAR surveys (CHAMP). Pit <br /> designs based on current mine designs <br /> 3. Manning's n <br /> Description Nfaruill Q's 11 - <br /> Trees Q.()7 <br /> RiVer 0.033 (vemize) �1 <br /> Open land 0.0; Trees 0 0� <br /> Ed¢es 0.0" (dense) <br /> Ponds 0.02 Trees 0.065 <br /> Residential 0.075 (,l,ar,e <br /> Parkin¢lot 0.065 Ri%e1 U 033 <br /> Road 0.022 <br />