Laserfiche WebLink
<br />• year flood peak was found to be 570 cfs, but was rounded to 600 c s for ease <br />of use. The 25-year flood is unlikely to have any major impacts pon the mine <br />site. The Middle Fork of the South Platte River has a well-defin d river <br />valley, and as can be seen on Plate No. lA, the river comes very lose to the <br />recirculating pond embankment in one location, but elsewhere is 1 toted some <br />distance Erom the pond embankment and other mine activities. The embankment <br />crest is approximately 22 feet above the river at the point where the river <br />nears the embankment. It is unlikely that river flooding upstrea of the pond <br />embankments could result in overbank flow that could find its way to the <br />ponds. In addition, a field survey found the toe of the north end of the <br />embankment to be 8 foot above the river. Cross section AA in Pla No. lA was <br />taken at the critical area of the South Platte. Riprap was placed at a height <br />of three feet per the Corps of Engineers, then a five Foot walkwa followed <br />with two feet of riprap at the toe of the embankment. <br />Accordingly, the river "threatens" the pond embankment only at the point where <br />the rivet and the toe of the embankment are immediately adjacent t each <br />other. Since our earlier report indicated a flood level of approx mately four <br />Feet will occur, the toe of the embankment has been riprapped toe elevation <br />of flue to six feet above the normal river water elevation to prot ct the <br />embankment in the event of the 25-year flood. A bench, or flat ar a, has been <br />included in response to a request from the Corps of Engineers to p ovide a <br />vegetation and access route alongside the river. This is seen in action AA <br />on Plate No. IA. <br />• MIATER BUFFET DITCR <br />The MLRD requested additional information regarding the conveyance of water <br />from the source ditch to the sluice box and pond operations. An a isting <br />corrugated metal pipe serves as the offtake From the source ditch. This <br />existing pipe delivers water to the top of what is known as the Co orado <br />Springs Cut in the vicinity of the old wash pond. The Colorado Sp ings Cut is <br />an approximate 100 foot wide "valley". The bottom of this "valley contains a <br />dirt road as well as a small meandering waterway. This waterway f ows at <br />approximately LX slope and is the means by which water leaves the xisting <br />pipe and is conveyed to the point at which it is pumped under high pressure to <br />the Ross box. The area traversed by this waterway is a previously mined area <br />and is primarily gravel and cobbles not subject to erosion. Shoul any <br />sediment be picked up by this waterway, its ultimate destination 1 the <br />recirculating pond where the aedinente will settle out. <br />This supply ditch has been used historically as an effective and e~ficient <br />means of supply. Due to its location, any potential failure of th supply <br />ditch would be captured in the recirculating pond should such an u likely <br />event occur. <br />• <br />4 <br />