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peak flow for both Gregory Gulch and North Clear Creek using a storm generated runoff method. The OA&A report formed the basis of the current Black Hawk Flood Insurance Study. In 1987, the Colorado Water Conservation Board wrote the second study, a flood hazard identification report for Central City. A storm runoff method, similar to the method employed in the OA&A study, was used. In 1991, Central City retained Rocky Mountain Consultants (RMC) to write a hydrology and hydraulic study. The RMC study was the third hydrology study and is more detailed than the previous studies. It still employs a storm runoff analysis, but the study area is divided into 17 sub-basins and analyzed with HEC-1, a network model. RMC also routed flows through the culverts and flumes in the system, and attempted to model the flow which backed into the streets. Several drainage improvements were recommended including the construction of the Dorothy Lee Reservoir. The reservoir reduced the OA&A peak flow estimate of 1240 cfs for Gregory Gulch at the Central City limits, to 969 cfs. The drainage recommendations by RMC were adopted by Central City including the development of the Dorothy Lee Reservoir. Peak flow estimates by RMC were adopted by FEMA in the 1994 Central City Flood Insurance Study. In 1993, Futura produced the fourth study for Gilpin County. It was an analysis of North Clear Creek, below the Gregory Gulch flume. The results were submitted to FEMA for review. In the Futura report, a regression equation was developed from gage data on similar streams. The flow estimate for North Clear Creek using regression equations, was approximately one-third of the flow estimate calculated by OA&A using a storm runoff method. In 1995, COOT prepared the fifth hydrology study. The hydrology study addressed Clear Creek below Black Hawk, near the Gilpin County border. COOT developed a regression equation from a frequency analysis of stream gage stations on North Clear Creek and Clear Creek. Peak flow estimates from this study, like the Futura study, are less then storm generated runoff estimates. The COOT flow of 2,050 cfs is higher than the Futura value of 1,460 cfs. B. Reports Associated with Gregory Gulch Several reports listed in Table 1 used peak flow estimates, but did not carry out independent hydrology analysis. The first study in this category is the FEMA Flood Insurance Study for Black Hawk, which was written in 1984. The FEMA report is based on the 1980 hydrology study by Owen Ayers & Associates. The 1984 report predates the addition of the Dorothy Lee Reservoir (1991) above Central City, so it does not reflect the 270 cfs flow reduction which the reservoir produces. The FEMA peak flow estimate for Black Hawk, near the Central City limit, is still 1240 cfs. 8