PERMFILE66219 - Laserfiche WebLink

Home Browse Search

Routt County Commissioners June 4, 2001 Page 5 of 8 Yampa River channel ranging in depth from approximately 7.7 to 9 feet. As a result of this large channel depth, the conveyance capacity is shown to be sufficient in XS-1 and XS-4 to prohibit water from rising above the channel bank. But the BFE does rise above the channel bank in XS-2 and XS-3. Even without questioning the accuracy of the assumed cross-sections, the BFE above the banks at XS-2 and XS-3 would cause portions of the property to be inundated. This cause and effect of flooding on to the property has not been adequately addressed. In the Applicant's report, on page 5 of 7 its stated that overflow does occur at XS-1, XS-2, and XS-3. The Applicant rationalizes that overflow will be intercepted by an existing Swale that parallels the river, thus keeping the property out of floodplain. This is anill-conceived assumption. Although not stated in the report, both the Yampa River and Trout Creek were modeled as having subcritical hydraulic gradients, evident by review of Table 2 in Appendix A and B of Applicant's report (i.e., W.S. Elev. is greater than Critical W.S.). When modeling a subcritical gradient, the modeling analyses begins downstream and then steps sequentially upstream. Consequently, a backwater curve develops starting downstream and works its way upstream. Any Swale that parallels the river would have water backed-up into it at the same BFE as in the river. There is no place for a Swale to divert water. For a Swale to effectively remove flood flows (i.e., reduce the BFE) would require the diversion of water into a completely different drainage basin. Obviously this is not the case at this location on the Yampa River. Hence, the rationale that a Swale will remove overflows is simply without merit. 2. Trout Creek The hydrology for Trout Creek needs to be corrected before any evaluation ca^. be made as to floodplain delineation. Because recent field observations contradict the water surface cross-sections shown in the Applicant's report, the field survey data ofthe river cross-sections needs to be reviewed for accuracy. Federal and State Permitting In Part II ofthe Federal Register Department of Defense, under Section 404 ofthe Clean Water Act, the secretary of the Army, acting through the Chief of the Engineers, is authorized to issue permits after notice and opportunity for public hearings, for the discharge of dredged or fill material into the waters of the United States. Additionally, under Section 401 of the Clean Water Act any applicant for a federal license or permit to conduct any activity that may result in a dischazge of a pollutant into waters ofthe United States to obtain a certification from the State in which the discharge originates. Should it be determined the Applicant's property is within the 100-year floodplain, then federal permit and public interest review will be required as per Sections 404 and 401 of the Clean Water Act. It appears to AES that there are sufficient inaccuracies and inconsistencies inthe Applicant's Floodplain