HYDRO30209 - Laserfiche WebLink

Home Browse Search

17 • 4 WINDY GULCH DATA ASSESSMENT 4.1 Flow characteristics of Windy Gulch Windy Gulch is a small stream with varying flow characteristics. The upper reach of Windy Gulch (ie above the WGU Weir) flows through a high alpine meadow within a U-shaped valley above the Bachelor Mountain road (see Plan 2.1). Flow within this reach is generally perennial in nature except possibly during extended dry periods. The stream is fed by snowmelt, surface runoff, and groundwater discharge from the meadow area to the stream. Downstream of the WGU Weir, the stream enters a steep talus slope composed of rhyolite. At this point, the stream quickly disappears into the talus. There is no channel or surface flow in this reach, even during relatively high flow periods. This talus slope continues to the upper portions of the 9700 dump, which was at least partly constructed on talus. This constitutes the non-flowing middle reach of the stream. • Flow again surfaces below the 9700 dump which starts the intermittent portion of the stream. Within the intermittent reach of the stream, part of the flow entering from the upper drainage area remains subsurface in alluvium. Thus, as shown in the stream hydrographs (Appendix B), the 9700 Weir consistently has lower flows than the upper WGU Weir. Just below the 9700 Weir, surface flow is diverted past the 9360 dump via a large culvert, and is returned to the surface channel just above DPI. Flows again begin to resurface below DP-0, as the bedrock is nearer the surtace and the alluvium deposits in the gulch appear to thin. Consequently, there appears to be a slight gain in surface flows in this reach of stream as noted by the minor increase in overall flow recorded in the WGL Weir as compared with the flows recorded at the 9700 Weir. However, it is unlikely that this slight increase in flow reflects water from deeper alluvium or bedrock given the thinning of alluvium, the more pronounced exposure of bedrock, and the diurnal fluctuations (discussed below) observed in the lower reaches of Windy Gulch. Consequently, nearly all water flows at the WGL Weir have had contact with shallow, mineralized alluvium. Water level measurements were taken at each drive point piezometer, and wells HW-1 and HW-2, and then compared to the elevation of the adjacent creek bed as shown in Table 4.1. In all cases but one, the water levels in the drive point or well were lower than the elevation of the creek bed. The exception was well HW-2, which had some water level measurements slightly above (0.25 ft) the creek bed during the spring runoff. Overall, however, evidence from each installation suggests that Windy Gulch is a losing stream through it's middle and lower reaches.