19 - Drainage Presentation - Sandy Creek Upper Tributaries 4 and 6

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The location where Tributaries 4 and 6 meet near 26t' Street SE and Simpson: 1`rNftary 6 is a 25 -foot wide cup ( rete -lined, trapezoidal channel Yvith a,.unafl curve at the cnfiUence With m° irmwtar rt (flgure 4The ecrmilrauenciek is e wide area of flooding In time FOAA effective flood rnap as wwweV as the re0semf existing condition model el (see Appen&x ). Cobb Fendley's analysis included combining city survey and lidar data with FEMA's hydrologic and hydraulic models from the 1970's. Most of FEMA's data was on microfiche. This old microfiche data was converted for use in HEC -RAS Version 4. 1.0 (Hydraulic Engineering Center — River Analysis System), the industry standard in flood modeling. They applied the hydraulic models to the existing Flood Insurance Rate Map (FIRMs), which had been last updated in 2011. The effective FEMA FIRM Map was modified using the data that Cobb Fendley modeled, and the "Special Flood Hazard Area (Commonly referred to as the "100 -year floodplain") shrank significantly". They recommended several projects, and ran a proposed model through HEC -RAS, resulting in the 100 year floodplain shrinking significantly. This however came with an approximate price tag of $10.2 Million. The report did discuss an immediate and inexpensive step that would potentially reduce home owner's insurance need. Cobb Fendley discussed the process of revising the Special Flood Hazard Area to current conditions based on their combination of survey, lidar, and microfiche data, and how "Letter of Map" Amendments (LOMAs) could be sent to FEMA to revise the floodplain to no longer require flood insurance for some properties. I contacted Cobb Fendley about an updated fee and scope of services to provide what is needed to proceed with these LOMAs. Their estimate was $10,000 to update their data with current conditions and work with FEMA to amend the flood map. This would help give homeowners more options with their future insurance, and/or lower existing insurance rates. Going back to the two 2016 flood events, Cobb Fendley discussed the following interesting facts about flood gauges on the Sulphur River downstream: "The United States Geological Survey (USGS) has 2 stream gages in the same drainage basin (Big Cypress — Sulphur Basin) as Big Sandy Creek Tributaries 4 and 6. Gage 11