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same amount of water is then spread over an area 5 to 7 <br />times its present size, the flow rate will decrease by at <br />least 3 times. The same volume of water wil '' <br />1 be presen~ bum <br />the pit area will act as a retention area slowing the <br />associated flow rates. <br />Dcwnstream erosion. scouring and related impacts will <br />aot occur, as stream flows of the high water channels will <br />be reduced before they leave the pit site. Eastern and <br />northern. bank erosion, will also be reduced as a result of <br />lower flow rates and lowering the flood channels elevations. <br />The outflow of the flood waters will travel over 100 feet of <br />undisturbed material before discharging onto the Imhoff <br />property ir. the same location it now does. <br />Siltation is aot a significant problem it this portico <br />of the River as the silt content of this bar is <br />.nsigaificant. A screen test of the gravel bar content was <br />performed in August, 1991, with the following results: <br />Screen Size WeiGht Percent <br />greater than 6" 25.4 <br />6" to 1" 33.8 <br />1" to 5;8" 8.3ro <br />5; 8" to S;lE" 23.4 <br />less than 1;16" 9.1~ <br />Less than 10~ of the material passes through a 1;16" screen. <br />th;.~ an ~nsigrificant amount of silt-sized maters^l (1; 1E mm <br />- 200 mess sieve) is present on this site. The farce <br />percentage of E" and larger materials contained in this bar <br />results in very stable banks. This is also why the ben„s <br />previously constructed on the west bank of the River have <br />withstood mercus flood events. <br />To help pre%ent any per.;.anent river course change. Peck <br />will leave a ben:.. SO feet wide and 2 to 5 feet high unmined <br />ad;acert to the eastern edge of the River. This berm will <br />be sloped 3 tc 1 towards the pit. See Exhibit E-1 Mir.irg <br />Plan for location and thickness of the berms. This berm <br />will be maintained during each year of mining. Peck will <br />reconstruct any berg area which might be destroyed during <br />the previous season'^ flood prior to mining. With over 25b <br />of the gravel material being over 6" size, the ben:., will <br />withstand the normal high water staces of the River without <br />substantial erosion. This berm is not designed to prevent <br />flooding from a 50 year or a 100 year event. Berm design to <br />accomplish this would require much larger and heavier <br />reinforcements which would be very detrimental to the <br />surrcundirg properties. The Peck Miring Plan intends to <br />allow the River to flow unimpeded during flood stage. The <br />only purpose of this berm is tc prevent any permanent river <br />ccurse charge. The Peck Mining Plan further intends to keep <br />the River in its present location during and after mining. <br />FLOODING: <br />Each year during the spring runoff season portions of <br />the permit area are inundated by spring runcff flood waters <br />from the Uncompahgre River. The amount and extent of <br /> <br />