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December 22, 1998 watershed is not at all uniform in its hydrologic characteristics as you proceed from upstream to downstream. Box Elder Creek is one of several streams that originate on the Palmer Divide (also known as the Monument Ridge) and then flow north tcward the South Platte River. Because of the significant altitude at the top of this ridge (at some locations it is slightly over 7500 feet above sea level), it is an obvio1.;$ feature to be considered in determining whether an area is hydrologically homogeneous or not. I think that comparisons between Box Elder Creek and any stream, that do not originate on the Palmer Divide should only be made with extreme caution. Overall, Box Elder Creek is long and narrow. Unfortunately, even that characterization is oversimplified. The basin is actually shaped somewhat like a lollipop, with a larger, rounder area al the headwaters (near the Palmer Divide) and a narrow area downstream. The location where the shap\: changes from round like the "sucker" part of a lollipop to long and narrow like the "stick" part of a lollipop is also the location where vegelation, soils, geology and slope change. AI! of these peculiarities are likely reasons why the calculaled peak flows increase in direct response to increased drainage area in Elbert County bUl do not increase in response to increases in drainage area in Arapahoe and Adams Counties. When I discussed the hydrology of Box Elder Creek with Larry Lang, he offered one other unique attribute of the watershed that was sig;nificant in his mind. He said that the watersheds farther east than Box Elder Creek, principally the various branches of Bijou Creek, have clay soils, while Cherry Creek and Box Elder Creek have sandy soils. He feels that the watersheds with clay soils could be expected to produce more runoff than the watersheds with sandy soils. Interestingly, Cherry Creek may provide an answer to the question, "Is theR already convincing evidence that the CUHP results for Box Elder Creek are rea:,onable?" I recall from the original analysis by FEMA, the data set for their regression included a gage on Cherry Creek. That gage has a drainage area that is very close to the drainage area of Box Elder Creek at 1-70. The Cherry Creek gage 100-year flow is quite similar to the CUHP flow for Box Elder Creek. In addition, Cherry Creek is essentially the next door neighbor watershed to the Box Elder Creek watershed. At the time that 1 observed those facts, and today, 1 saw no need to ask any more questions. Based on historic gage results on Cherry Creek, 1 conclude with l:WO thoughts: I) there is already a valid, scientific basis for accepting the Urban Drainage flows that requires no further research on anybody's part; 2) comparison of flow values for Box Elder Creek to any regression values from large geographi(: areas like all of Eastern Colorado is both unnecessary and inappropriate. 2 II II II II II II II :1 I I I I I I I I I I