2012-11-09_REVISION - M2010049 (3)

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Western Sugar Reclamation Land Development Project Flood Analysis III. PROJECT DESCRIPTION AND POTENTIAL FOR SITE FLOODING 3.1 Project Description The project has been previously described via past submittals to DRMS, and thus won't be discussed in this report. However, some project drawings are included in the Appendix for reference. 3.2 Potential for Site Flooding It is important to note that all flood data and information are based on the FEMA Effective Flood Insurance Study (FEMA, 1999), and the most recent US Army Corps of Engineers HEC -RAS study (USACE, 2008). Because this information is the approved FEMA Effective Flood Insurance Study (FIS), no further flood analysis was performed as such would be contradictory to the Effective study and not approved by FEMA. The 100 -year flood (Q = 7,080 at the site) does not break out of the right bank of the CLPR in the vicinity of the Site until entering a reach between Ash Avenue and the Ogilvy Ditch Diversion Dam. This flow would move from west to east through the Site. There are no detailed HEC -RAS cross - sections in that reach to substantiate the flooding in detail (Appendix I). The HEC -RAS water surface profile through the reach is actually below the channel bank grade. But again, the data and information used is from the FEMA Effective FIS and thus is adopted for the purpose of this study. Any additional flood study would need to be approved by FEMA before adopted — a very expensive and time - consuming process. River Station 26048 (See Appendix) does not indicate right overbank flooding (which would enter the Site). However, RS 24159 (See Appendix) — which is the approximate center of Tract C - does indicate right overbank flooding. Such flooding is questionable because a berm runs along the right channel bank (See Appendix) that is higher than the 100 -yr water surface elevation (WSEL). Thus, it is important to note that flows may not spill overbank in that reach.. Thus, this flood impact analysis is considered conservative because further detailed HEC -RAS study may indicate no or minimal flooding onto the Site. One - hundred year discharge onto the site is based on right overbank flow from RS 24159 (See Appendix) which is about 900 cfs. Such discharge is the basis for flood analysis in this study. IV. HEADCUT MODELING AND BERM WIDTH ANALYSIS 4.1 Methodology A special study was performed to evaluate headcutting and berm width for site - specific conditions on Tract C. More specifically, the berm will be treated as an earthen dam crest and the pit side wall the face of a dam. Thus, the berm will be evaluated as an "earthen dam" such that breach computer modeling technology can be applied. Such modeling will use site - specific soil physical parameters, flood inflow hydrograph, and state -of -the -art methodology to evaluate headcutting in the pit and scour over the berm. pg. 5