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i i <br />same amcunt 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 will be present but <br />the pit area will act as a retention area slowing the <br />associated flow rates. <br />Downstream erosion. scouring and related mpacts will <br />not 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 reduce3 as a result of <br />lower flcw rates and lowering the flood channels elevaticns. <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 ~t now does. <br />Siltation is not a sig..^.ificant prcblem in this portion. <br />of the River as the silt content of this bar is <br />insignificant. A screen test of the gravel bar ccntert was <br />performed in August, 1991, with the following results: <br />Screen Size Wei4ht Parcent <br />greater than 6" 25.5 <br />6" to 1" 33.8 <br />1" to 5'S" 8.3.x, <br />5; E" to 1;16" 23.4 <br />less than 1/16" 9.1ro <br />Less than 10~ of the material passes through a 1;16" screen, <br />thus an insignificant amcunt of silt-sized material (1;16 mm <br />- 2CC mess sieve) is present on this site. The lance <br />percentage of 6" and larger materials contained in this bar <br />results in very stable barks. This is also why the berms <br />previously constructed or. the west bank of the River have <br />withstood numerous flood events. <br />To help pre~.ert any permanent river course change, Peck <br />will leave a berm 10 feet wide and 2 to 5 feet high ermined <br />adjacent to the eastern edge of the River. This berm will <br />be sloped 3 to 1 towards the pit. See E::hibit E-1 Miring <br />Plan for location and thickness of the berms. This berm <br />will be maintained during each year of mining. Pec'.: will <br />reconstruct a..^.y berm area which ,night be destroyed during <br />the previous season's flood prior to mining. With cver 25ro <br />of the gravel material being over 6" size, the berm will <br />vrithstand the normal high water stages 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 r..uch larger and heavier <br />reinforcements which would be very detrimental to the <br />surrounding 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 />course change. The Peck Mining Plar. further intends to keep <br />the River in its present locaticn during and after mining. <br />FLOODING: <br />Each year during the sprang runoff season portions of <br />the permit area are inundated by spring runcff flood waters <br />from the Uncompahgre River. The a.:,ount and extent of <br /> <br />