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<br />J' ""-0. <br /> <br />Mr. Rick Higgins <br />Page 2 <br /> <br />The improvements consist of widening the main channel along the left bank from station 13+70 <br />up to station 16+90. Hydraulically, this improvement appears to lower the lOa-year water <br />surface by up to 0,7S feet or so compared to the revised existing conditions model. The action <br />would clearly remove the River Pines subdivision from the regulatory lOa-year floodplain based <br />on the modeling results, I have no objections to the concept of lowering the lOa-year water <br />surface by making physical modifications along the subject reach. However, my original feeling <br />was that modifications could be made to the channel overbank instead of the channel itself. Any <br />modifications to the streambank below the ordinary high water line may have adverse impacts <br />that would require environmental permitting. In addition, it is unclear as to whether the <br />modifications are proposed on private property and, if so, are the property owners willing to <br />allow construction to take place? <br /> <br />Lastly, the post-project lOa-year water surface elevations downstream of station 13+00 are <br />higher than those in the effective FIS. FEMA will require that all property owners along the <br />affected reach be notified of the proposed water surface increase. <br /> <br />In summary, I have no major objections to the proposed concept of removing the River Pines <br />subdivision from the regulatory lOa-year floodplain, It appears that a change to the FEMA <br />floodplain mapping is justified based on MWE's revised existing conditions model and the <br />proposed channel improvements. Even if the proposed improvements are implemented, some <br />residents in the subdivision who live along the right bank of the creek may feel the need to <br />protect their property with temporary flood control measures during future high water events. <br />However, due to the low variability of streamflow in Tenmile Creek, there is only a difference of <br />210 cfs between a lOa-year event and a SOO-year event. The threat of catastrophic flooding <br />along Tenmile Creek under existing basin conditions is minimal. <br /> <br />Please call me if you have any questions or concerns about this issue. <br /> <br />Sincerely~ <br />~/~ /<,..-? .~ <br />~ ./ ,-- <br />/~..P'T"~ / ,;r<__' <br />~homas W, BrownH:fg;P.E. <br />Flood Control and Floodplain Management Section <br /> <br />cc: Brian Kolstad, McLaughlin Water Engineers <br />John Liou, FEMA Region 8 <br /> <br />C:Isec.llomr reviewslfrisco3-98.doc <br />