First floor elevations of buildings were collected from two regions in Biloxi. The first region was between Division St (north), Oak St (east), Howard Ave (south) and Caillavet St (west) and data were collected between 8/1/2019 and 7/31/2020. The second region, added at the ask of the City of Biloxi, was bound by Back Bay Blvd (north), Oak St (east), Division St (south) and Main St (west) and data were collected between 8/1/2020 and 7/31/2021. First floor elevations were collected through a combination of acquiring elevation certificates, taking GPS field measurements and calculating building elevations with street level imagery analysis. GPS field measurements were conducted in March 2020, whereas street level imagery were collected from August 2019 through July 2020, and then again in April and May 2021 in the project extension area. Street level imagery data were created through interpretation of Google Street View images, following the methodology provided by Needham and McIntyre (2018). Historical flood elevations for the city of Biloxi were collected through primary and secondary sources that included reviewing historical newspapers, official damage reports, sampling during storm events, and scientific literature. This process built upon data construction begun in Needham and Keim (2012) and Needham et al. (2013). Observation-driven water elevation return frequencies were developed based on the historical flood elevations using the log-linear regression method, determined to be the most accurate for calculating the frequency of extreme water levels in Needham (2014). A time series of historic floods for Biloxi required the establishment of Mean Sea Level. GPS field measurements taken in March, 2020, revealed that MSL was approximately 0.60 feet above NAVD88 datum. A histogram that shows how much saltwater each hurricane or tropical storm pushed above sea level for the year of the storm, removed the influence of long-term sea level rise in Biloxi. Following guidance from the Northern Gulf of Mexico Sentinel Site Cooperative, the rates of sea level rise used in this study were 0.0074 ft/ year from 1880-1994, then 0.0442 ft/ year from 1994-2021. Biloxi has no long-term tide gauge, and our understanding is that those sea level rise rates are estimates that take into account the rate of sea level rise at Bay Waveland Yacht Club to the west and Dauphin Island to the east of Biloxi. The datasets were combined to identify structures that were not elevated above specific water elevation return frequencies both now and with three sea level rise scenarios for the year 2060: intermediate-low, intermediate and intermediate-high. Localized sea-level rise scenarios were provided by Mississippi State University at this link: https://webapps.msucares.com/slr/ Rates of sea level rise from years 2000-2060 were given as 1.07 feet for intermediate-low, 1.75 feet for intermediate and 2.48 feet for intermediate-high. We estimated Mean Sea Level to be -0.28 feet in the year 2000, using sea level rise rates provided by the Northern Gulf of Mexico Sentinel Site Cooperative. This provides sea level estimates of 0.47 feet, 1.15 feet, and 1.88 feet above NAVD88 datum in the year 2060, for intermediate-low, intermediate and intermediate-high sea level rise rates, respectively. We subtracted 0.60 feet, the mean sea level for 2020, from each of these levels, to estimate future sea level rise changes.
Data were collected to inform City of Biloxi floodplain management, response, and recovery efforts to current-day floods and to support planning action for the City of Biloxi planner.
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