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III- 3 A peak discharge of I, 730 cfs and tp at Eldorado Springs of four hours were developed. The reasonableness of these figures was checked utilizing other hydrologic tools such as flood frequency analysis of flows on South Boulder Creek, comparison with historic flow data at stream gages in the region, and evaluation of parameters used to develop the flows on Boulder Creek by the Corps of Engineers. Similar results were obtained with these more approximate methods. The Commons dimensionless hydrograph(l)was used with the peak flow of 1,730 ds and the runoff pattern to develop the hydrograph at Eldorado Springs re sulting from the 100-year storm. This same procedure was used to develop hydrographs at two additional points downstream to determine the variation in peak flows and hydrograph slopes as the flood moves down the stream channels. The other points chosen to determine the extent of this variation were at the Boulder Turnpike and the confluence with Boulder Creek. The flatter slopes downstream of Eldorado Springs necessitated a modification to the unit hydrograph which would reflect the reduced peaks and increased travel time. This modification was accomplished by us ing a procedure developed by the Soil Conservation Service which modified the parameters used in establishing the shape of the hydrograph. The peak flows resulting from storms of various return intervals at various locations along South Boulder Creek are shown in Table 2 on the following page. The I OO-year flood flows, shown on Table 2, compare with the Corps of Engineers study which determined the Intermediate Regional Flood for present conditions, equivalent to the 100-year flood, to be 5,000 cfs at both Eldorado Springs and the confluence with Boulder Creek. The flows for Marshall and Viele Gulches were developed using the CUHP method. Since they are relatively small drainage basins that may become urbanized in the future, they have hydrographs with high peaks of short duration. Since these peaks will occur much earlier than the peak in South Boulder Creek, their combined effect is less than the sum of their peaks. It should be noted that the above-mentioned hydrographs assumed that there will be no flow into South Boulder Creek from Bear Creek. During a major storm, a portion of the flows from Bear Creek presently enter the South Boulder Creek basin by way of the Empson Ditch. For purposes of this study, it was assumed that the City will be able to follow previous recommendations by others to insure that this water will flow (I) G. G. Commons, Flood Hydrographs, Civil Engineering, Volume 12, p. 571, 1942.