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Gypsum Loan Feasibility Outline CWCB Water Project Loan Program Page 12 of 33 2.3.1 Water Availabilitv a. Hvdrolo~ic Yield One significant consideration to be ma.de as part of any evaluation of alternatives is the hydrologic yield available to the reservoir. Previous hydrologic yield analyses were conducted from 2002 to 2005. These analyses estimated yield by proration of discharge measurements from nearby watersheds on the sole basis of drainage area ratio as determined for LEDE Reservoir by hand delineation from topographic quadrangles. An underlying assumption of this method was reliance on elevation and proximity to approximate precipitation and runoff characteristics. As the discharge measurements which were used originated from gage sites situated well below the relative position of LEDE Reservoir, the discharge estimates were skewed down due to less precipitation and runoff in the lower portion of the gaged drainages. On this basis it was formerly estimated that the hydrologic yield physically and legally available for diversion and storage in LEDE Reservoir was about 615 acre-feet (ac-ft) annually on average. As just described, this is believed to be less than may actually be available. Therefare, a new hydrologic yield analysis has been prepared using information which was not accessible at the time of the previous analyses. While there is no substitute for site measurement, evaluation methodologies have significantly changed in the last few years. Gypsum ha.s also been in the progress of obtaining actua.l field data in recent years. LEDE Reservoir stores water from two small catchments: the catchment directly up- gradient of the embankment in the headwater area of the Gypsum Creek watershed, and the catchment up-gradient of the headgate of the LEDE Ditch in the headwater area of the Antones Cabin Creek watershed. Neither catchment is monitored by a flow measurement station, so no site specific historical discharge data is available for hydrologic analysis. The only historical flow data available are diversion records, which do not accurately reflect the hydrologic yield, as they are based on infrequent observations of diversion and storage operations as conducted historically without the benefit of accurate measuring devices, upgraded infrastructure or the need to supply water for municipal uses. Although there are no flow measurement stations on the subject catchments, there are similar watersheds nearby for which high quality discharge data are available for a meaningful period of record. Given the lack of site specific data, the best available means of estimating the yield of the catchments which supply LEDE Reservoir is correlation based on hydrologic parameters to the similar nearby watersheds from which discharge is measured. Two such watersheds are Beaver Creek and Cross Creek. These watersheds are not only nearby but also have slope and aspect characteristics similar to the LEDE Reservoir catchments as well as flow measurements covering meaningful periods of record more recent and complete than those of the gaged basins used in the previous analyses. Surface water discharge from Beaver Creek has been measured consistently since the early 1970s by the USGS Beaver Creek at Avon, Colorado gage, site number 09067000. Surface water discharge from Cross Creek has been measured