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FEMA Region III Storm Surge Project

FEMA Region III Storm Surge Project. Return Level Results and Historical Comparison. FEMA Region III Coastal Workshop USACE- Field Research Facility November 1, 2011. Michael Forte USACE-ERDC. Advancements. 2010 Finite Grid 30-40m Minimum Resolution. 1978 Triangular Finite Grid

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FEMA Region III Storm Surge Project

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  1. FEMA Region III Storm Surge Project Return Level Results and Historical Comparison FEMA Region III Coastal Workshop USACE- Field Research Facility November 1, 2011 Michael Forte USACE-ERDC

  2. Advancements 2010 Finite Grid 30-40m Minimum Resolution 1978 Triangular Finite Grid 5-10km resolution

  3. FEMA Tropical & Extratropical 100yr Return Levels • Delaware Bay, Eastern Shore of VA • and Southern Chesapeake Bay • (Norfolk & Tidewater VA) • contain the highest surge levels • throughout Region III. • Lowest return levels at Middle • Chesapeake Bay All UNITS ARE IN US FEET

  4. 100Yr Historical Return Levels Still Water Elevation (SWEL) Compiled by Dewberry from multiple Flood Insurance Studies throughout Region 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 Region III 100yr results

  5. 100Yr SWEL Comparison FEMA 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 upper • Chesapeake Bay and VA Eastern Shore • (- 1.5 – 3.5ft) • Overall good agreement with a couple of important differences

  6. SWEL Comparison Scatter Plot of Region III and Historical SWEL values

  7. Why the changes? • Storm track • Historical gauge analysis • Historical Studies for Delaware Bay • were 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 basin • with few tributaries allowing water • to pile up.

  8. Why the changes? • Storm track • Historical gauge analysis • Historical Studies for Delaware Bay • were 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 basin • with few tributaries allowing water • to pile up.

  9. Why the changes? • Storm track • Historical gauge analysis • Historical Studies for Delaware Bay • were 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 basin • with few tributaries allowing water • to pile up.

  10. Region II & Region III 100Yr Level Comparison Region II 100Yr Modeled Output Region II Modeled output compared With Region III

  11. Region II & Region III 100Yr Level Comparison Another Encouraging Result! • Majority of points are within +/- 1 foot. • Two modeled outputs from two • different teams, run on two different computers = VERY GOOD • AGREEMENT

  12. Region III minus Region II Histogram

  13. 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

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