2019-08-21_REVISION - M1976056 (6)

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McAtee Construction Company Riverside Pit M-1976-056 August 20, 2019 BANK PROTECTION PLAN This bank protection plan covers two areas in the Riverside Pit that lie within 400 feet of the South Platte River or the Lowline Ditch head gate area that were affected by the flooding in 2013 . While this flood was greater then a 100 year event the damages done to the South Platt River corridor has had long term affects to the Riverside Pit that requires McAtee Construction Company to take certain precautions to keep the river or ditch from capturing the lakes that will remain after reclamation is complete . We have followed the 1987 Urban Drainage and Flood Control District (UDFCD) Publication guideline document for planning and design of the armoring on the lake side bank and the inlet spillway on the south end of Lake Robert . McAtee Construction Company has no control over the river banks or ditch bank as they are not on property owned by McAtee . So we can only protect on site areas, but after the 2013 flood the Lowline Ditch company placed new armoring along the west bank of the ditch wherever it was damaged by flooding. This primarily took place from the old head gate down ditch, to where the ditches return flow structure was damaged just south of the original permit line . We believe the chances of the ditch capturing the lake area is remote as this would prevent delivery of irrigation water to the areas north of the mine . The ditch company had constructed a large return flow spillway to the south of the eastern parcel to keep this from happening. The flood levee and armoring done many years ago from the Highway 6 bridge north to the old head gate, survived the flood and are intact . Much of this lies along the east side of the permit area. McAtee Construction Company had no control over how the armoring along the levee or ditch was done so we do not know what criteria was used when doing the work. This plan is prepared to protect the lake banks within 100 feet of the ditch/river front from damage during and after a flood event . We have no information on the flow velocities or volume of flows for a 100 year event in this stretch of the river. During past 100 year events the mined area did not flood directly from the river/ditch but rather the ground water elevations came up to inundate the area. In the 2013 event (1000 year) the water elevation in the mine area was approximately 3 feet deep. What flood water that did enter the site came as sheet flows across HWY 6 to the south. Review of the most recent FIRM maps show that the 100 year flood elevations in this area should be nearly 7 feet above the existing ground surface according to our measurements . For example they have a flood elevation line along the south side of the Lake Robert area that shows the 100 year elevation should be 3935, yet the ground elevation is 3928 and even in 2013 the water was not 7 feet deep on this area . We believe they have used an elevation datum that is different from