2-08CW056 Supplemental Data - Laserfiche WebLink

Home Browse Search

• • Hydrologic Data TU conducted a preliminary evaluation of the stream hydrology to determine if water was physically available for an instream flow appropriation. Daily discharge in Severy Creek (Fig. 1) was estimated from gage data collected from both North Cascade Creek and South Cascade Creek (Fig. 1) using synthetic hydrology. Although the watersheds of both North and South Cascade Creek are somewhat smaller than the Severy Creek watershed with a slightly lower mean elevations, their general aspect, slopes, mean annual precipitation, and forested areas are quite similar (Table 3). Because Severy Creek has a higher mean elevation, it likely has a greater snowpack than either branch of Cascade Creek. This suggests that daily discharge estimates for Severy Creek based on North and South Cascade Creek are likely to be conservative. Table 3. Comparison of selected basin characteristics from Severy Creek, North Cascade Creek and South Cascade Creek. Parameter Units Severy Creek North Cascade Creek ou Cascade Creek Area that drained by stream miles 3.39 1.98 1.86 Maximum Basin Elevation feet 12900 10500 10800 Minimum Basin Elevation feet 8360 8590 8590 Mean Basin Slope, computed from 10m DEM % 38.8 32.2 36.6 Change in Elevation feet 4520 1910 2220 Mean Basin Elevation feet 9910 93201 9360 Stream Aspect* ENE ESE ENE Mean Annual Precipitation unadjusted inches 22.6 1 19.8 22.5 Forested Area % 80.81 94.4 94.1 All statistics ca cu a e using the Ubub utility o ora o StreamStats ( http: / /streamstats .cr.usgs.gov /costreamstats) with the exception of Stream Aspect* which was visually estimated using watershed maps. Colorado Springs Utilities (CSU) has maintained flow gages on both North and South Cascade Creeks since 1949. CSU has recorded the daily discharge for both of these creeks on more than 99% of the days between 10 /1 /49 and 9/30/06. Trout Unlimited used the discharge data from each stream (North Cascade Creek and South Cascade Creek) to provide two independent estimate of the daily discharge rate in Severy Creek for the period of record. The mean of each of these two estimates was taken as the best estimate of the daily discharge through Severy Creek on a given day. Thus, for any given day between 10/1/49 and 9/30/06, there are three estimates of daily discharge through Severy Creek: one based on North Cascade Creek, one based on South Cascade Creek, and the mean of these two estimates. Average daily discharge for each calendar day was calculated from each of these three estimates of daily discharge. Average daily discharge was calculated as the mean of the estimates of daily discharge for that day of the year for the period of record (typically 57 estimates). These estimates were then compared to the recommended flows. Regardless of the streams used to estimate flow, estimated average daily discharge through Severy Creek always exceeds the recommended flows (Fig. 2).