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flooding depends on the amount of snow melt ardor thunderstorm activity. Historically measured high discharge on the Uacor..pahgre River occuzs during the months of May and; or Jure and range from 200 cfs to 1740 cfs. Spring runoff occurs from as early as May 1 to as late as September 10, depending o.^. the snowpack in the area. High flows resulting from tl^.,:nderstorms can occur any ti:.,e frc~. 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 of the gravel bar to be mined. Flooding from these flows is 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 charnels ranoed from 0.5 cfs to 1.2 cfs. The most recent extreme high flow of 1740 cfs occurred on June 24, 1983 and resulted ir. the gravel bar to be mined being exposed. During that flood year the River channel expanded east of the ncn-al channel by 300 feet (Plate 12, Ouray County 1950 Flood Plain Study). Associated sheet flows extended several hundred feet east of this boundary. This flood year may represent a 50 year or a 10C year flood evert. The Curay County Flood Plain Study of 1978 indicates that a 10C year flood would raise the water levels ir. the River in this area by 6 1;2 to 7 feet. It would also spread sheet flows between 1500 and 2500 feet beyond the main River channel (see Plates 12 and 27 of the Ouray County Flood Plain Study). While this mining operation will help reduce the potential of flooding on the eastern. and northern. boundaries during average runoff high flow conditions, the helpful effects would be minimal or non-existent during a 50 or 10C year flood. Peck Inc. makes n.o promises ccrcerninc increased flood protection during such everts; but, by lesser.irc flood channel stream discharge and removing gravels from the bar adjacent to the main River channel, erosion on the eastern and northern. 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 1933 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 mir.irg 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 mined. These will be installed prior to mining ir. a particular area of the pit. These will be installed to a depth of 3 feet below the low 0