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2019 South Environmental Report – Volume I Appendix 2-2

Appendix 2-2: Hurricane Irma, September 8–11, 2017, Impact on Water Management System

Wossenu Abtew and Chelsea Qiu1

INTRODUCTION Documenting hydrologic events such as hurricanes, storms, and droughts provides supporting information for water management decision making and evaluating the vulnerability of infrastructure. The 2017 hurricane season was an active year with from the islands to the mainland with destruction and losses of life recorded. In 2017, there were 17 named storms with 10 hurricanes (6 of which were major hurricanes), and 7 tropical storms (Figure 1). Of these 17 storms, the South Florida Water Management District (SFWMD or District) area was most impacted by Hurricane Irma. Hurricane Irma developed around 16o N latitude and 28o W longitude near the Islands on August 30, 2017, and later intensified to a Category 5 hurricane. It caused catastrophic damage to and the before impacting and making in the on September 10, 2017, as a Category 4 storm. Hurricane Irma caused catastrophic damage before crossing the Florida peninsula for a second landfall in the United States near Marco Island as a Category 3 hurricane (Figure 2). Irma was one of the costliest hurricanes on record in the Atlantic basin with a total of seven landfalls with four as a Category 5 (Cangialosi et al. 2018). Table 1 shows the range of wind speeds for hurricane Categories 1 through 5 and number of 2017 tropical storms and hurricanes.

Table 1. 2017 tropical systems and categories.

Wind Speed Number of Category Type (miles per hour) Storms <35 Tropical Storm 6 Category 1 74–95 Hurricane 4 Category 2 96–110 Category 3 111–130 Category 4 131–155 Major Hurricane 6 Category 5 ≥155

1 The authors acknowledge Tracey Piccone for assistance in accessing emergency management reports and pictures and reviewing the report; and Eric Swartz for providing material and reviewing the report.

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Figure 1. 2017 hurricane and tropical storm paths and durations (Cangialosi et al. 2018).

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Figure 2. Hurricane Irma’s path August 30–September 10, 2017. (Original source: National Hurricane Center satellite montage of Hurricane Irma using geostationary satellite infrared images and National Hurricane Center advisories. Courtesy of University of Wisconsin Cooperative Institute for Meteorological Satellite Studies.)

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RAINFALL FROM HURRICANE IRMA Daily rainfall is reported from SFWMD operations rain gauge network from 7:00 a.m. the previous day to 7:00 a.m. the reporting day. Theissen weighted areal average rainfall is also reported for each rain area (Figure 3). Rainfall from Hurricane Irma started on the morning of September 8, 2017, when the center of the hurricane was east of the (Figures 1, 2, and 4a). The Florida Keys and the southern tip of mainland Florida started getting rainfall with a District average of 0.2 inches (7:00 a.m. September 8 to 7:00 a.m. September 9) and 3 inches in National Park (ENP). Most of the rainfall from Hurricane Irma over the District occurred from 7:00 a.m. on September 9 to 7:00 a.m. on September 11 (Figures 4a through 4c and Table 2). As shown in Figures 4b, 4c, and 4d and Table 2, the highest rainfall areas were generally areas closer to the west and south; Southwest Coast, ENP, East Caloosahatchee, East Everglades Agricultural Area, and West Everglades Agricultural Area (Figure 5). However, the Martin/St. Lucie area received one of the highest rainfalls from Hurricane Irma as a band of rainfall concentrated on that area ahead of the hurricane landfall. The Palm Beach rain area was spared from high intensity rainfall bands as shown in Figures 4b and 4c. Figure 4d depicts total rainfall for the major impact days September 9 to 11, 2017. The highest rainfall at a site from the hurricane was in ENP at rainfall station N-206 (21.79 inches) followed by the Southwest Coast and East Caloosahatchee at station HRNDRFILL (18.92 inches). The highest rainfall in Martin/St. Lucie was at station FPR (17.08 inches; Figure 6).

Figure 3. SFWMD rainfall areas.

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Figure 4. Rainfall from Hurricane Irma (a) September 8 to 9; (b) September 9 to 10; (c) September 10 to 11 (7:00 a.m. to 7:00 a.m.) and (d) September 9 to 11 (7:00 a.m. to 7:00 a.m.).

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Table 2. Hurricane Irma daily average rainfall in inches over rain areas and the District.

3-Day Dates (7 a.m. to 7 a.m.) Rain Area Area Average September 8–9 September 9–10 September 10–11 Southwest Coast 10.84 0.11 2.13 8.60 10.15 2.99 7.05 0.11 Big Cypress Basin 9.94 0.14 3.34 6.46 East Caloosahatchee 9.52 0.08 2.37 7.07 West Everglades Agricultural Area 9.20 0.32 4.21 4.67 Martin/St. Lucie 9.03 0.42 4.97 3.64 Water Conservation Areas 1 & 2 7.99 0.05 4.76 3.18 Upper Kissimmee 7.97 0.25 0.64 7.08 Water Conservation Area 3 7.89 0.11 3.73 4.05 Lower Kissimmee 7.61 0.13 2.52 4.96 Broward 7.61 0.05 4.42 3.14 7.36 0.19 3.01 4.16 -Dade 7.24 0.63 3.24 3.37 East Everglades Agricultural Area 7.09 0.18 4.00 2.91 Palm Beach 5.85 0.06 3.05 2.74 District Average 8.39 0.20 3.04 5.15

Figure 5. Average rainfall from Hurricane Irma by rain area and overall (September 8–11, 2017).

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Figure 6. Highest rainfall from Hurricane Irma at a site within each rain area.

HURRICANE IRMA WIND OVER SFWMD In SFWMD’s weather stations, wind is measured every 10 seconds and wind speed and gust speed are recorded every 15 minutes as breakpoint data. The National Oceanic and Atmospheric Administration (NOAA) average wind speed measurement is at 1.5-meter (m) height every 2 seconds and averaged every 5 minutes (https://www.ncdc.noaa.gov/crn/measurements.html). The American Society for Testing and Materials (ASTM) standard one second wind measurements to capture wind gust speed (usually lasts for 3 seconds). The SFWMD weather station locations are shown in Figure 7. A typical SFMWD weather station (L006) in Lake Okeechobee is pictured in Figure 8. The maximum wind gust speed and wind speed at SFWMD weather stations during Hurricane Irma are shown in Table 3.

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Figure 7. SFWMD weather stations and Hurricane Irma direction.

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Figure 8. SFWMD weather station L006 in Lake Okeechobee.

Table 3. Maximum wind gust speed and wind speed at SFWMD weather stations. a

Maximum Gust Maximum County Basin Station Wind Speed Wind Speed (mph) (mph) Miami-Dade WCA-3A 3AS3W 86 68 Martin C-23 ACRAWX 65 48 Collier Faka Union AVEMAR 89 65 Palm Beach S-2, S-6, S-7 BELLW 71 51 Hendry S-4 CFSW 69 49 Palm Beach C-51E FHCHSX 77 44 Martin Kitching Creek JDWX 40 21 Okeechobee Lake Okeechobee L001 75 61 Glades Lake Okeechobee L005 78 63 Palm Beach Lake Okeechobee L006 71 60 Palm Beach WCA-1 LX 67 45 Palm Beach Lake Okeechobee LZ40 77 60 Broward STA-5/6 ROTNWX 75 54 Broward WCA-3A S140W 64 43 Miami-Dade L-31NS S331W 70 50 Osceola Lake Tohopekaliga S61W 80 42 Okeechobee S-65E S65DW 73 53 Glades C-40 S75WX 78 55 Glades East Caloosahatchee S78W 75 51 Clades Faka Union SGGEW 97 54 St. Lucie St. Lucie North SVWX 56 35 St. Lucie Ten Mile Creek TMCWX 66 45 Polk Lake Hatchineha WRWX 56 41 a. mph – miles per hour and WCA – Water Conservation Area.

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Wind speed over the District area was dependent on the location of stations relative to the path of the hurricane, forward speed, and characteristics of the wind field. The highest wind gust speed was in the southwest and south (Figures 7 and 9). Wind gust speed in the middle of the District area south of Lake Okeechobee is shown in Figure 10. Wind speed in the northwest, upper east coast, and northern portions of SFWMD are shown in Figures 11 through 13.

Figure 9. Hurricane Irma wind gust speed in miles per hour (mph) in the southern part of the SFWMD area. Wind gust speed peaked at 4:00 p.m. on September 10, 2017).

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Figure 10. Hurricane Irma wind gust speed in the middle of the SFWMD area south of Lake Okeechobee. Wind gust speed peaked at 4:15 p.m. on September 10, 2017.

Figure 11. Hurricane Irma wind gust speed in the northwest part of the SFWMD area. Wind gust speed peaked at 7:45 p.m. on September 10, 2017.

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Figure 12. Hurricane Irma wind gust speed in the eastern part of the SFWMD area. Wind gust speed peaked at 4:30 p.m. on September 10, 2017.

Figure 13. Hurricane Irma wind gust speed in the northern part of the SFWMD area. Wind gust speed peaked at 11:15 p.m. on September 10, 2017.

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HURRICANE IRMA IMPACTS ON LAKE OKEECHOBEE Maximum wind gust speed over Lake Okeechobee was close to 80 miles per hour (mph). Figure 14 depicts Hurricane Irma wind gust speed at four weather stations inside the lake and wind direction at one of them (L006). Lake Okeechobee is the part of the South Florida water management system most susceptible to hurricanes. It can be impacted by wind-driven that could potentially damage the earthen dam. High rainfall and associated high runoff from hurricanes can raise water levels too high where the risk of seepage from the earthen dam increases. At high water levels, daily seepage inspection and mitigation are conducted by the United States Army Corps of Engineers. During high inflow rates when the region is wet, the lake inflows are higher than the capacity to release from the lake resulting in continuous water level rise. There are also potential water quality impacts from high winds as sediment resuspension can increase turbidity and nutrient concentrations. Increase in turbidity limits growth of submerged vegetation by reducing light penetration depth. High winds can damage submerged vegetation affecting the lake ecologically. In general, damage to desired flora and fauna is an ecological impact of hurricanes over the lake.

Figure 14. Hurricane Irma wind gust speed and direction over Lake Okeechobee.

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Hurricane winds over a lake push water in the wind direction resulting in drawdown upwind and storm surge on the edge of the lake in the wind direction. Hurricane Irma peak wind gust was from the southeast to the north and northwest (Figure 14). A stage difference of 10.81 feet (ft) was created from the S-352 spillway at the southeast corner of the lake to the S-131 pump station to the northwest of the lake (Figures 15 and 16). The fetch distance between S-352 and S-131 is 29.5 miles along the prevailing southeast wind direction (Figure 14). A stage difference of 9.68 ft was created from the S-2 pump station at the south of the lake to the S-65E spillway on the Kissimmee River to the north of the lake (Figures 14 and 15). The fetch distance between S-2 and the mouth of the Kissimmee River is 31.6 miles and S-65E is 39.5 miles, but not right along the main wind direction (Figures 14 and 16). Tailwater at S-65E and S-65EX was raised to 20.03 ft National Geodetic Vertical Datum of 1929 (NGVD29) and bank erosion damaged the tailwater stage monitoring platform from wave runup (Figure 17). The S-65E spillway is 8 miles north of the bank of the lake on the Kissimmee River/C-38 canal. The importance of bank protection around structures was observed. drops during hurricane events. As pressure decreases, wind speed increases. Low air pressure over the lake is an additional factor for wind setup. Wind setup occurs when sustained wind blows over a water surface. Wind setup increases with wind speed and fetch. Air pressure fluctuation at three sites, southwest (SGGEW), west (S78) and over Lake Okeechobee (L006) is depicted by Figure 18.

Figure 15. Hurricane Irma wind impact on Lake Okeechobee water level.

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Figure 16. Lake Okeechobee stage monitoring sites used for wind setup calculation.

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Figure 17. Erosion damage to the tailwater monitoring platform at the S-65E spillway at the mouth of the Kissimmee River 8 miles from the Lake Okeechobee inflow point.

Figure 18. Atmospheric pressure fluctuation during Hurricane Irma in the southwest and northwest areas and Lake Okeechobee.

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WATER LEVELS AND FLOWS The high volume and high intensity of rainfall from hurricanes can exceed the drainage removal capacity of water management systems resulting in high water levels in canals, detention ponds, lakes, and other storage usually resulting in flooding. Hurricane Irma’s rainfall intensity and runoff generation resulted in a sharp rise of water levels in lakes and Everglades Water Conservation Areas (WCAs). Lake Okeechobee, the main storage in the South Florida water management system, received 1,192,609 acre-feet (ac-ft) of inflows, which is 56% of the historical average annual inflow, in one month (September 2017), mostly from Hurricane Irma. The for the same period was 262,679 ac-ft (18% of the historical average annual outflow). At the same time, the lake water level rose by 2.87 ft (Figure 19) increasing the risk from a following hurricane event and seepage. The stage rose from the Baseflow Subband to the High Subband of the lake regulation schedule. WCA-1 stage increased by 0.57 ft and stayed in Zone B of the regulation schedule (Figure 20). WCA-2A stage increased by 1.08 ft and was above both above the temporary and Zone B regulation lines. WCA-3A stage increased by 1.07 ft and stayed above the Zone A (top) regulation line. Stage in WCA-3A was impacted by Hurricane Irma, after a wet June followed by a wet October, which resulted in ecological impacts from high water conditions. Extensive water management efforts were required to draw down stages within the normal seasonal range. Some of the main impacts of the high water conditions were water being too deep for wildlife such as deer and stress to vegetation on tree islands. On June 23, 2017, the Florida Department of Environmental Protection (FDEP) issued an emergency final order (EFO) to manage high water conditions resulting from the unusually high rainfall in June. The EFO continued through the hurricane season as water levels increased further in Lake Okeechobee and the Everglades Protection Area from Hurricane Irma and other rainfall events.

Figure 19. Hydrologic impact on Lake Okeechobee, flows, and water levels following Hurricane Irma.

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Figure 20. Hydrologic impact on WCA water levels following Hurricane Irma.

FLOODING AND OTHER IMPACTS ON THE WATER MANAGEMENT SYSTEM This report is limited to flooding impacts on the water management system. Because of the high rainfall intensity from Hurricane Irma, there was extensive flooding in several parts of SFWMD and for extended periods in some cases. Major flooding occurred in the southwestern, northeastern, southeastern, and northern parts of SFWMD and other pocket areas (Figure 21). Extensive damages occurred from flooding. Some of the hurricane impacts on the water management system included fallen trees in canals, which affect access and conveyance (Figure 22a and 22b). Quite commonly, levees and structure banks were eroded (Figures 22c, 23b, 23c, 23d, and 24a). Other damages occurred to pump stations where damage interfered with the performance of the pumps (Figure 22d). Field station damages were also reported (Figure 24d). In the Lower Kissimmee, the access road to the S-65A structure was flooded and damaged (Figure 23a).

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Figure 21. Flooding incidents from Hurricane Irma reported to the District’s Emergency Management Center (some flooded areas may not be shown on map).

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Figure 22. Some examples of Hurricane Irma impacts are shown in these photos. These impacts include (a) a fallen tree in the C-51 canal, (b) a fallen tree in the C-13 canal, (c) bank damage along the S-72 canal, and (d) damages to the G-310 pump station roof.

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Figure 23. Some examples of Hurricane Irma impacts are shown in these photos: (a) S-65A access road flooding and washout, (b) C-25 canal bank erosion, (c) C-41 canal bank erosion, and (d) C-14 canal bank erosion.

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Figure 24. Some examples of Hurricane Irma impacts are shown in these photos: (a) C-23 canal bank erosion, (b) Faka Union Canal bank erosion, and (c) a flooded community along Shingle Creek, and (d) West Palm Beach Field Station structure damage.

IMPACT ON EVERGLADES STORMWATER TREATMENT AREAS Impacts of hurricanes to the Everglades Stormwater Treatment Areas (STAs) include vegetation uprooting and dislocation (Figures 25a, 25b, 27a, and 27b), which results in dead vegetation, flow short- circuiting, and reduction in performance. Some STA cells are predominantly submerged aquatic vegetation (SAV), which are part of the phosphorus reduction system. Hurricane winds disrupt SAV by dislodging and dislocating affecting plant density and viability as a treatment system (Figures 26a and 26b). Wind and associated waves resuspend sediment in the STAs resulting in increased surface water nutrient concentrations. Figures 28a and 28b show sediment resuspension in STA cells.

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Figure 25. STA-1 West Cell 4 cattails before and after Hurricane Irma (photos by N. Ralph and W. Larson).

Figure 26. (a) STA-2 Flow-way 3 (mid flow-way) pre- storm SAV density and b) post-storm reduced density (photos by N. Ralph and W. Larson).

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Figure 27. Uprooted vegetation from Hurricane Irma in (a) STA-1 East Cell 2 and (b) STA-1 West Cell 4 (photos by N. Ralph and W. Larson).

Figure 28. Sediment resuspension from Hurricane Irma in (a) STA-1 West Cell 5B and (b) Cell 2B (photos by N. Ralph and W. Larson).

SUMMARY Hurricane Irma made landfall over as a major hurricane and impacted the region with reported wind speeds higher than 100 mph and over 20 inches of rainfall at one site. Its impact on the SFWMD area was significant with high rainfall, increased water levels in lakes and WCAs, disturbance to the Everglades STAs, flooding, and structural damages. In this report, rainfall intensity and amount, increased flow, and rising water levels in the SFWMD area are presented as well as wind gust speeds over the region from different sources including SFWMD weather stations. This report covers the hurricane impact on the South Florida water management system and includes examples of water management infrastructure damages.

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LITERATURE CITED Cangialosi J.P., A.S. Latto and R. Berg. 2018. Hurricane Irma, National Hurricane Center Report. AL112017, National Hurricane Center, Miami, FL.

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