US Army Engineer Research and Development Center

FEMA Region III Storm Surge Project

Return Level Results and Historical Comparison

Michael ForteUSACE-ERDC

FEMA Region III Coastal Workshop

USACE- Field Research FacilityNovember 1, 2011

US Army Engineer Research and Development Center

1978 Triangular Finite Grid5-10km resolution

2010 Finite Grid30-40m Minimum Resolution

Advancements

FEMA Tropical & Extratropical 100yr Return Levels

• Delaware Bay, Eastern Shore of VAand Southern Chesapeake Bay (Norfolk & Tidewater VA)contain the highest surge levelsthroughout Region III.

• Lowest return levels at Middle Chesapeake Bay

All UNITS ARE IN US FEET

100Yr Historical Return LevelsStill Water Elevation (SWEL)

Compiled by Dewberry from multiple Flood Insurance Studies throughoutRegion III

Sources:

USACE – Potomac (DC area)VIMS – Majority of Chesapeake Bay NWS- Hydro (Gauge analysis)USGS – (WL Gauge analysis)Grenier Engineering (WLGauge analysis)

Compare existing/historical with RegionIII 100yr results

100Yr SWEL ComparisonFEMA R3 minus Historical

•Majority of values +/- 1 foot when Compared to Historical Study

•Elevated Return Levels in Delaware Bay and Lower Chesapeake (Norfolk) (+ 1.5 – 3.5 ft)

•Decreased Return Levels in upperChesapeake Bay and VA Eastern Shore(- 1.5 – 3.5ft)

• Overall good agreement with a couple of important differences

US Army Engineer Research and Development Center

SWEL Comparison

Scatter Plot of Region III and Historical SWEL values

Why the changes?

• Storm track• Historical gauge analysis

• Historical Studies for Delaware Baywere based on gauge analysis with very few to no tropical systems occurring.

• Tropical Storm tracks –winds drive water South down the Chesapeake Bay

• Delaware Bay acts as a catch basinwith few tributaries allowing waterto pile up.

Why the changes?

• Storm track• Historical gauge analysis

• Historical Studies for Delaware Baywere based on gauge analysis with very few to no tropical systems occurring.

• Tropical Storm tracks –winds drive water South down the Chesapeake Bay

• Delaware Bay acts as a catch basinwith few tributaries allowing waterto pile up.

Why the changes?

• Storm track• Historical gauge analysis

• Historical Studies for Delaware Baywere based on gauge analysis with very few to no tropical systems occurring.

• Tropical Storm tracks –winds drive water South down the Chesapeake Bay

• Delaware Bay acts as a catch basinwith few tributaries allowing waterto pile up.

Region II & Region III100Yr Level Comparison

Region II Modeled output compared With Region III

Region II 100YrModeled Output

Region II & Region III100Yr Level Comparison

Another Encouraging Result!

• Majority of points are within +/- 1 foot.

• Two modeled outputs from twodifferent teams, run on two different computers = VERY GOODAGREEMENT

Region III minus Region II Histogram

US Army Engineer Research and Development Center

FEMA Region III Storm Surge Project

Summary/Conclusions

• Excellent agreement with historical SWELS with a few important differences

• Region II Compares well with Region III