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<br />_._. "___._.._0 __.' ,-"-.____.._ _____ _____+ "._'__"_""-_'_--",",__~_4_'.""'__ ".__._.__;......._U___~.~~_.~_______._._.:._____~........._'.___ "._......~__ __~......_;<~_~""...._._ j __ U <br /> <br />Fourmile Canyon Creek, cross sections are nonuniform for the few crossings with piers. <br />For high flows, in some cases, examination of the data showed the pressure/weir solution <br />was unstable or otherwise gave unrealistic results. This could be the result of decreasing <br />the opening through modeling blockage coupled with changing flow regimes, including <br />changing critical and subcritical regimes in the multiple profiles. For those instances, <br />energy was used for the high flow option to produce a stable solution. <br /> <br />Small path crossings over the channel were assumed to be obstructions without <br />conveyance below the top of the path. These crossings were usually hard coded into the <br />HEC-RAS model, which can result in the appearance of an inverse slope for a short <br />distance in the profile. <br /> <br />3.2.1.4 Irrigation Ditches <br /> <br />Fourmile Canyon Creek channel is bisected by a number of irrigation structures. <br />Following procedures recommended by UDFCD, the irrigation ditches are assumed to <br />flow full and the top of bank of the ditch is coded when the ditch crosses the channel. In <br />some instances, diversion structures are located in the channel. For these instances, the <br />structures were hard-coded based on survey data into the cross section. Both of these <br />circumstances can result in the appearance of an inverse slope for a short distance in the <br />profile. <br /> <br />3.2.1.5 Floodway <br /> <br />It should be noted that it has been agreed by the City of Boulder, Boulder County, <br />UDFCD, the Colorado Water Conservation Board (CWCB), Michael Baker Jr. and <br />FEMA (see email correspondence below) that a one-half foot (1/2') rise floodway would <br />be published for both Fourmile Canyon and Wonderland Creeks as that is the criteria that <br />has been used by the City of Boulder for more than three decades and the County has <br />agreed to this because the vast majority of the lands under these floodplains/floodways <br />are located either in the City of Boulder or its direct planning/development area. <br />Boulder County has been provided with a I-foot rise model and I-foot rise delineation <br />should any properties within these two streams require permitting until such time as they <br />are annexed into the City of Boulder. <br /> <br />From: Sacbibit, Patrick [mailto:Rick.Sacbibit@dhs.gov] <br />Sent: Wednesday, January 04, 2006 1:32 PM <br />To: Kevin Doyle; Rick Sacbibit (FEMA) <br />Cc: Dave Jula; Anne McDaniel; bdegroot@udfcd.org; Carlson, Dan; Kevin Long (FEMA); <br />meddek@ci.boulder.co.us; nlove@loveassociates.com <br />Subject: RE: <br /> <br />Kevin, <br /> <br />In this situation, FEMA cannot restrict the maximum allowable surcharge in Boulder County below <br />1.0 foot if the county does not have local ordinances in place that are more stringent than the <br />Federal limit. Although I understand the City of Boulder's situation, they cannot regulate the <br /> <br />-17- <br />