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6. River Protection <br />As is seen by the river location near the pit, there is a sharp outside bend in the river very neaz the <br />proposed pit. Although the pit will maintain a minimum 100' buffer from the toe of low water in the <br />river to the edge of excavation, embankment protection for this area of the river is still wazranted <br />for long term stability. This will ensure that the river never erodes into the lake during a lazge flow <br />event. <br />Therefore, a minimum durable angular rock of minimum size Dso = 4.50 feet size is specified for a <br />length of 225 feet and a slope length of 16 feet as shown in the diagram below. The landowner has <br />in the past placed many large rock and concrete slabs of this approximate size in a portion of this <br />azea. This has provided good protection but more material is needed laterally and vertically. Also, <br />more material needs to be embedded in the bank to prevent scouring. The maximum slope of the <br />embanlanent will be 2H:1 V. - <br />The rock will be either awell-cemented sandstone or igneous/metamorphic rock that is durable. It <br />will be placed as shown on the diagram below and Map E-1 Mine Plan. The top elevation of the <br />protection riprap is5598.0 feet, which is approximately 1.5 feet below the elevation of the 100 year <br />flood at this particular location in the river. This elevation was estimated from the US Army Corps <br />of Engineers/FEMA floodplain maps for the North Fork of the Gunnison River at Paonia. This re- <br />port does not have a determination of the velocity of the 100 year peak flow event, however, the <br />CSU procedure used to evaluate the rock stability makes an estimate based on river dimensions, <br />slope and roughness. The size of the boulders were analyzed using the CSU procedure, which sums <br />the moments azound a pivot point and calculates the turning forces in a given condition to determine <br />a safety factor. A safety factor is calculated for a boulder in a normal bed and on a sideslope. The <br />calculations are presented below: <br />North Fork Pit Mazch 04 22 <br />