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f 1/ Ie ( . . - , Ms. Sheila Beissel June 6. 1990 Page two For most of your basins that are smaller than 1 square mile (the majority of the basins you studied) the unit discharge is about 1.200 c.f.s./square mile. For the S.C.S. that figure would be about 300 c.f.s./square mile. Given the care you put into your analysis and the "high-density" land-use assumptions you made. we see no reason to dispute your higher flows for these smaller basins simply because the S.C.S. figures are lower. The one basin where the land use assumptions you used vary substantially from the 50 perce,nt impervious area assumption is Basin I. There some of your flows are similar to flows the a.c.s. might have derived. or even lower. For Basin 1 (approximately 5 square miles) your flow is 1.320 d.f.s. and S.C.S.' flow would be about 700 c.f.s., For Basin 11 your drainage area (3.230 acres) appears to be incorrect; 230 acres seems a more reasonable figure. We Ciinnot comment other than to say that for 230 acres your flow wuuld be higher than the SCS' flow. For Basin 12 (apprDximately 4 square miles) your flow is 790 c.f.s.. and the S.C.S. I flow would be about 640 s.f.s. For Basin 1201 (approxirr~tely 2 square miles) your flow is 290 c.f.s. and S.C.S.' '..ould be abclU1: 410 c.f.s. Clarification on the area for Basin II and comments on the "low flow" for Basin 1201 would help us understand your analysis better for those two locations. For Basins Band C. Table 3 did not include drainage area or flow information for th'e dow'nstream point where all branches combine. In the case of Basin B that would represent about 245 acres. and for Basin C that would represent about 300 acres. It may be that this informiition was lE!ft. out b,ecause the land at the north end of Battlement Mesa is steep and may remain open space. We would ask :Eor a't least a comment on these two basins and their hydrology. We appreciate your sending us the information from the 1975 Frasier & Gingery report. We agree with you that your findings were reasonably consistent with those original findings. It appears that different engineers arrived at similar flows given similar land-use assumptions. In summary. for Basins Band C we have som'e questions we would like addressed. For Basins D-H we do n011: object to your flows. They are reasonable given the kind of development that exists and that is anticipated for Battlement Mesa. For Basin I. even though our concerns are not serious. we would appreciate some additional infol:mation to addr(~ss those concerns.