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McAtee Construction Company Riverside Pit <br /> M-1976-056 July 19, 2022 <br /> BANK PROTECTION PLAN (Updated) <br /> This bank protection plan covers two areas in the Riverside Pit <br /> that lie within 400 feet of the South Platte River or the Lowline <br /> Ditch head gate area that were affected by the flooding in 2013 . <br /> While this flood was greater then a 100 year event the damages <br /> done to the South Platt River corridor has had long term affects <br /> to the Riverside Pit that requires McAtee Construction Company to <br /> take certain precautions to keep the river or ditch from <br /> capturing the lakes that will remain after reclamation is <br /> complete. <br /> We have followed the 1987 Urban Drainage and Flood Control <br /> District (UDFCD) Publication guideline document for planning and <br /> design of the armoring on the lake side bank and the inlet <br /> spillway on the south end of Lake Robert . McAtee Construction <br /> Company has no control over the river banks or ditch bank as they <br /> are not owned by McAtee. So we can only protect on site areas, <br /> but after the 2013 flood the Lowline Ditch company placed new <br /> armoring along the west bank of the ditch wherever it was damaged <br /> by flooding. This primarily took place from the old head gate <br /> down ditch, to where the ditches return flow structure was <br /> damaged just south of the original permit line. We believe the <br /> chances of the ditch capturing the lake area is remote as this <br /> would prevent delivery of irrigation water to the areas north of <br /> the mine . The ditch company had constructed a large return flow <br /> spillway to the south of the eastern parcel to keep this from <br /> happening. The flood levee and armoring done many years ago from <br /> the Highway 6 bridge north to the old head gate, survived the <br /> flood and are intact . Much of this lies along the east side of <br /> the permit area. McAtee Construction Company had no control over <br /> how the armoring along the levee or ditch was done so we do not <br /> know what criteria were used when doing the work. This plan is <br /> prepared to protect the lake banks within 100 feet of the <br /> ditch/river front from damage during and after a flood event . <br /> We have no information on the flow velocities or volume of flows <br /> for a 100 year event in this stretch of the river. During past <br /> 100 year events the mined area did not flood directly from the <br /> river/ditch but rather the ground water elevations came up to <br /> inundate the area. In the 2013 event (1000 year) the water <br /> elevation in the mine area was approximately 3 feet deep. What <br /> flood water that did enter the site came as sheet flows across <br /> HWY 6 to the south. Review of the most recent FIRM maps show <br /> that the 100 year flood elevations in this area should be nearly <br /> 7 feet above the existing ground surface according to our <br /> measurements . For example they have a flood elevation line along <br /> the south side of the Lake Robert area that shows the 100 year <br /> elevation should be 3935, yet the ground elevation is 3928 and <br /> even in 2013 the water was not 7 feet deep on this area . We <br /> believe they have used an elevation datum that is different from <br />