Laserfiche WebLink
MAY-19-04 14:25 FROM-WEISS AND VAN SCOYK 970 879 6058 T-286 P.030/033 F-562 <br />the structures. Only through caliUrating a hydraulic model to exisring conditians, will the <br />cumulative effecl of the cntire structure field he estahlished. <br />One possible method for providing a quantilication of potential long-lerm channel <br />adjustment would be to survey the reach containing the existing habitat stnictures <br />ttpstream of tJle boating parlc. Initial observations rnade during the site visit indicate thac <br />rnatZy oF thosz structures have been in place for a period of years. Comparing current <br />surveys with any pre-construction survey inFormation would provide valuable insigflt into <br />the potential for long-term clzannel adjustments and the corresponding impacts. <br />Mr. Browning's memo also raises the issue of structure staUility. Nowhere in the <br />review were calculations and/or procedures used to si2e lhe rock oF either the boat cliutes <br />or the habitat stnzetures f.ound. Constricting hydraulie scructures, whether providing a <br />horizon.tal or vertical eonstriction to llow, are exposed to varying hydraulic Forces over a <br />range of now eonditions. Typically, a flow corresponding Eo a lOQ-year rettun period is <br />specifed for design and component sizing. While this may represent the discharge of <br />interest in accordance with federal, state and local resulations, local hydra«lic Forces <br />resulting from llow velocity and boundary shear stress my noc be at a maximum dunng <br />this flow. As a structure becomes submerged, it's ability to provide a hydraulie conlrol is <br />diminished and therefore flow over, or around, the structure may not pass cluough critical <br />depth. As such, flows occu.rring at a much more frequent return periocl tlian the actuaI <br />design discharge may result iaz signifcaiitly higher hydraulic forces. Conducti.ng a <br />lhorough analysis ol the documented boating struct;urc failttres wauld serve to quantify <br />the critical design flow rates for each unique system. <br />In reviewing tllese documents, it is apparent chat fill has beeil placed in the <br />floodway. Zt is also evident that the conditions specified in the granting of 404 permit <br />number 2000175121 are in question. FEMA has well establisIied guidclines and <br />pxocedures for worlcing within a floodway and in reviewing the supplied information, ic <br />does not appear that the accepted scandard of engineering practice lias been met f.or the <br />construction of this projcct. It is strongly recommended that boch the immediate and <br />long-LE2Tt7 impacts af the entire structure field bE exaxnined and documented in <br />accordanee with federal, state and loeal guidelines. <br />Yi has been a pleasure providing this preliminary, independenl assessment for your <br />review. Should you require any additional inronnation, please dou't hesitaie to contact <br />Dr. Thornton at 970,491-8394 or Dr. Watson at 970-491-8313. <br />Kespectfully <br />ls/ Ghescer I. 7'hornton Ph.D P.E. <br />Christopher I. Thoi-nton, Ph.D., P.E. <br />/s/Chester C_ GVcrrson Ph.D_ P.L•. <br />Cltester C. Watson, Ph.D., P.E.