1997-11-24 - CC Packet - (Admin.)

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Ms. Kate Drewry September 5, 1997 Page 2 Appendix S�c�lan Z 7 Table 1 lists calculated composite curve numbers, both existing and future, for each sub- basin within the city. The text on page 12, states that a future `developed' condition in ScC l�c� 3.3 some of the sub - basins actually results in projections of decreased runoff when compared (NE - ;0 to existing row crop cover. Council staff finds this conclusion somewhat disconcerting - C[- 3 7 particularly in sub - basins CC -4 and CC -6 where significant increases in impervious CC -`! T surface coverage is planned. Sub -basin CC -4's developed condition curve number is CL- projected to drop from its existing 79 to 76, with planned conversion of the land (in Cc 7 - Centerville and Lino Lakes) to industrial, commercial, and high density residential uses 3.9 having average curve numbers of 88, 92, and 85, respectively (on `B' soils). Sub -basin (Z,d -F�) CC -6's deveioped condition curve number is projected to remain at 63, with planned conversion of most of the land to industrial uses. Council staff recommends that each of the sub -basin peak runoff flow calculations be reevaluated prior to inclusion in the final plan to insure accurate projection of future development - condition stormflows and flood levels. This letter completes the review process of the Metropolitan Council. If you have questions regarding these comments or wish to discuss them in greater detail, please contact James Larsen, P.E., Environmental Planning and Evaluation, at 602 -1159. Sincerely, y Helen Boyer Director, Environmental Services Division HB:jI c: Jim March, City of Centerville Dave Nyberg, MSA James Wychor, Metropolitan Council District 9 Keith Buttleman, Director, Environmental Planning and Evaluation Department Guy Peterson, Metropolitan Council Sector Representative