Blair S. Holloway NOAA/ Charleston, SC Why is Important?

• Repeated flooding poses a threat to property and infrastructure – Recent article in the Columbia Journal of Environmental Law details the challenges state and local governments across FL, GA, NC, SC face regarding infrastructure vulnerability due to sea level rise

• Clear trend of rising sea levels along the SE coast

• NOAA Technical Report “Patterns and Projections of High Tide Flooding along the US Coastline Using a Common Impact Threshold” NWS Charleston Coastal Program

• Monitor tide levels at 2 NOS tide gauges – Charleston Harbor (SC) – Fort Pulaski (GA)

• Watch/Warning/Advisory Products – – – Coastal NWS Charleston Coastal Flood Program

• Tide Forecast Guidance – Extra-Tropical (ETSS) – Probabilistic ETSS – Extratropical Surge & Tide Operational System (ESTOFS) – Tropical: P-surge, SLOSH (inundation)

• NWS Forecast – Total Water Level – Uses ETSS and ESTOFS as a starting point – Forecasters adjust a base tide anomaly to create the forecast Charleston Harbor Tide Gauge

• Coastal flood thresholds – Advisory level: 7.00-7.99 ft MLLW – Warning level: >8.00 ft MLLW

• Most impacts are in and around the Charleston peninsula

• In the 7.00-7.50 ft MLLW range, mostly minor impacts to roads

• At >8.00 ft MLLW impacts are more significant and widespread

• Site has only exceeded 8.00 ft MLLW 26 times since 1921 – 12 of these have come since 2015 Fort Pulaski Tide Gauge

• Coastal flood thresholds – Advisory level: 9.20-9.99 ft MLLW – Warning level: >10.00 ft MLLW

• Most impacts are in and around the Tybee Island area

• In the 9.20-9.60 ft MLLW range, mostly minor impacts

• At >10.00 ft MLLW impacts are more significant, including making HW-80 between Savannah and Tybee Island impassable

• Site has only exceeded 10.00 ft MLLW 13 times since 1935 – 6 of these have come since 2015 Coastal Flood Database

• Document date, time, and peak value of all tides that exceed coastal flood thresholds at Charleston Harbor and Fort Pulaski

• Able to go back to 1/1/1980 – 1/1/1980 to 11/30/1995 used NOS verified high/low water level – 12/1/1995 to present used NOS verified 6-minute water level

• Purpose was to provide data for media inquiries, etc.

• Interesting trends emerged

• Do current thresholds still make sense? • 828 total events identified through 2018 • 22 events so far in 2019 • Obvious increasingCoastal trend Flood Database • 1980’s: ~9 events per year • 1990’s: ~19 events per year • 2000’s: ~21 events per year • 2010’s: ~37 events per year • ~31% of all events (263/850) have occurred 2014-present • ~47% of all Coastalevents occurred in September Flood-November Database • ~63% of events are 7.29 ft MLLW or less Coastal Flood• ~17% of events Database are Moderate (7.50 ft MLLW) or higher • 294 total events identified through 2018 • 11 events so far in 2019 • Obvious increasingCoastal trend Flood Database • 1980’s: ~2 events per year • 1990’s: ~7 events per year • 2000’s: ~7 events per year • 2010’s: ~15 events per year • ~36% of all events (109/305) have occurred 2014-present • ~40% of all Coastalevents occurred in September Flood-November Database • ~57% of events are 9.39 ft MLLW or less Coastal Flood• ~19% of events Database are Moderate (9.60 ft MLLW) or higher Coastal Flood Projections

• What will coastal flooding look like in the decades to come with sea-level rise?

• Output using NOAA Technical Report NOS CO-OPS 086 projections (Billy Sweet, NOS)

• For Charleston, 2040: – Int. Low: 80-100 days – Intermediate: 100-170 days – Int. High: 170-250 days – High: 250-300 days – Extreme: 300-330 days Charleston Harbor Thresholds

• City of Charleston has deployed an effective check-valve system in many typical flooding hot spots

• Reduces flooding at the minor range (7.00-7.20 ft MLLW)

• In the future, do we want to bombard partners and the public with Coastal Flood Advisories?

• Continue working with the City of Charleston to see if coastal flood thresholds need to be increased