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Water Replacement Plan 12/21/83 Page Two SURFACE WATER HYDROLOGY The area of study lies within the upper main stem of the upper Colorado River region in Colorado. It lies within the sub-basin designated North Fork. High flows typically occur in the North Fork of the Gunnison River during May and June in response to melting snow packs. Flow rates during this period increase 5 to 10 times over those occurring during other months of the year, producing 60-65% of the annual flow. Low flows normally occur during the winter months when sur- face run-off is minimal and most of the flow represents groundwater discharge from the watershed. Tributary streams supporting agricultural activities typi- cally experience very low flows during late summer when irrigation demands are high, The North Fork of the Gunnison River, into which streams draining the area flow, is severely impacted 6y human activities, primarily agricultural. Irrigation has significant effects on water volune and quality by increasing salinity, nutrients, and probably herbicides/pesticide levels. The loMer flows also con- tribute to higher sunmer temperatures. The area lies within a region of generally dry climate. All but major streams in the area are of intermittent or ephemeral in character. Each individual water- shed basin will be described in detail within those sections. For further infor- mation on the North Fork of the Gunnison surface water, see Section 2.04.7(2), Orchard Valley Mine, Underground Mining and Reclamation Permit. Ponds Within the study area, very small ponds are Tocated. Most of these ponds are man-made and used for stock watering purposes. Each individual pond will be identified in the watershed basin in which it is located. Each pond has been field checked and inflows and water qualities have been monitored. Some of the ponds are supplied from spring sources. These sources are from the colluvium and do not represent any deep aquifer system. Sprin s Springs are sporadically located throughout the area. The springs were mapped and field checked. The discharges and qualities of the water were measured. The information on the springs is contained within the specific basin information. Many of the springs identified during the field reconnaissance dry up later in the year. All springs identified discharge from colluvial sources. None of them Mere iden- tified as tied to a deep aquifer system.