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support@civicplus.com <br /> Thursday, March 17, 2011 11:27 AM <br /> `RVCouncil; Margaret Driscoll; Bill Malinen <br /> Josephine Woods/Skaggs Online Form Submittal: Contact City Council <br /> 1 n form was submitted via your website: Contact City Council <br /> isephine Woods Development <br /> lard Skaggs <br /> 1160 Josephine Rd <br /> eville <br /> N <br /> you prefer to be contacted? Remember to fill in the corresponding contact <br /> n. . Email <br /> ess: : S <br /> er: : 651- <br /> 1 ire Your Comment, Question or Concern: I am contacting you about the proposed Pulti <br /> N development of Josephine Woods. My comment concerns the drainage report. The 1, <br /> 100 year return period precipitation design values used in the modeling appear to <br /> fated from maps originally published in David Hershfield's Technical Paper 40, <br /> firmed by a Pulti representative at the 2 March 2011 Planning Commission Meeting). <br /> two reasons to question the adequacy of Hershfield's estimates. First the most <br /> a used in that study was 1958. The precipitation climate of Minnesota has changed <br /> ter conditions in the intervening 50+ years. Second the analysis method used by <br /> combined hand curve fitting and the Gumbel distribution. Today, most <br /> ists believe that extreme precipitation distributions are heavy tailed and are <br /> with a Generalized Extreme Value distribution. I and a former student studied <br /> ecipitation over the Twin Cities area using a high density precipitation network <br /> by the State Climatologist. For a 10 by 10 KM area in which the project is <br /> ne GEV gives precipitation design values for 2, 10, and 100 year return periods of <br /> and 8.8 inches rather than the 2.8, 4.1, and 5.9 inches used in the modeling. In <br /> ;r, period from 1970 to 2003, the 2.8 inch 2 year return period value was equaled or <br /> n 23 years somewhere in the 10 KM square area when 16 or so times would be <br /> The 10 year value (4.linches) was equaled or exceeded 8 times versus an expected 3 <br /> s, and the 100 year value was exceeded once. <br /> objection to the proposed development. But I would like to see a more robust <br /> rid flood infrastructure built based on what in my opinion are more appropriate <br /> ' ion design values. I understand that the Rice Creek Watershed District and the <br /> ify the Hershfield estimates but surely as a minimum. In my opinion using the <br /> the modeling when there is substantial evidence that the Hershfield values now are <br /> rates reduces the initial costs to the developer but puts the city at risk for <br /> more frequent infrastructure repair costs. <br /> 1 <br /> 1 <br />