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flooding depends on the amount of snow melt nd;or thunderstorm activity. Histcrically measured high discharge on the Uncompahgre River occurs during the months of May and;cr June and range from 200 cfs to 1740 cfs. Spring runoff occurs from as early as May 1 to as late as September 10, depending on the snowpack i:, the area. High flcvrs resulting from thunderstorms can occur any time from April 1 to October 15. Site measurements over the past two high flow seasons (1990 and 1991) indicated a flow rate on the Uncompahgre of 220 cfs results in minor flooding cf the gravel bar to be mined. Flooding from these flows 's confined to the three high flow channels shown on Exhibit E-1. Water in these channels ranged from 0.5 feet to 1.5 feet deep and were from 2 to 10 feet wide. Flood season flow rates for the individual channels ranged from 0.5 cfs to 1.2 cfs. The most recent extreme high flow of 1740 cfs occurred on Jure 24, 1983 and resulted in the gravel bar to be mined being expcsed. During that flood year the River channel expanded east cf the normal channel by 300 feet (Plate 12, Ouray County 1980 Flood Plain Study). Associated sheet flows extended several hundred feet east of this boundary. This flood year ;..ay represent a 50 year or a 100 year flood event. The Curay County Flood Plain Study of 1978 indicates that a 100 year flood would raise the water levels in the River in this area by 6 1;2 to 7 feet. It would also spread sheet flows betweer. 1500 and 2500 feet beyond the main River channel (see Plates 12 and 27 cf the Ouray County Flood Plain Study;. While this mining operation will help reduce the potential of flooding on the eastern and northern bcundaries during average runoff high flow conditions, the helpful effects would be minimal or non-existent during a 50 or 100 year flood. Peck Inc. makes no promises concerning increased flood protectior. during such events; but, by lessening flood channel stream discharge and removing gravels from the bar adjacent to the mair. River channel. erosior. on the eastern and rcrthern banks will be lessened. It would take a flood flow of 2 feet deep spread over a 300 foot wide bar to erode the banks when mining is completed. This would be a similar flow to that of the 1983 high flow event. 2. HYDROLOGIC IMPACTS: The proposed berm 10 feet wide and 2 to 5 feet high left adjacent to the eastern edge of the River will keep the River out of the active pit during pit operations. All mining will occur at least one foot above the ground water table. To enable Peck to determine if ground water is present, monitoring pipes will be installed--at least three for each acre to be mired. These will be installed prior to mir.irg in a particular area of the pit. These will be installed to a depth of 3 feet below the low 0