Ed Curtis, PE, CFM, FEMA Region IX and Darryl Hatheway, CFM, AECOM ASFPM 2016, Grand Rapids, MI

Transcription

1 Methodology to Determine Process-Based Total Water Level Profiles in Areas Dominated by Wave Runup Ed Curtis, PE, CFM, FEMA Region IX and Darryl Hatheway, CFM, AECOM ASFPM 2016, Grand Rapids, MI

2 Thurs. June 23 Session J-8 2

3 Welcome and Introductions Wave Runup Depth and Velocity Grid Pilot Study California Coastal Analysis and Mapping Project Open Pacific Coast Study FEMA Region IX Edward Curtis Regional Engineer/Study Manager FEMA Production and Technical Services Contractor Team Vince Geronimo Project Manager Darryl Hatheway Technical Lead Jeremy Mull Coastal Engineer Sarah Kassem Coastal Engineer Elena Drei-Horgan Coastal Engineer Kristy MacDougall GIS Specialist 3

4 National Flood Insurance Program & Risk MAP

5 National Flood Insurance Program U.S. Congress established the National Flood Insurance Program with the passage of the National Flood Insurance Act of 1968 Community adopts and enforces a floodplain management ordinance to reduce flood risk to new and existing development in mapped floodplains Federal government makes flood insurance available to property owners in participating communities For more information on the NFIP visit 5

6 Risk MAP Vision To deliver quality data that increases public awareness and leads to action that reduces risk to life and property Objective (Coastal) To provide updated flood hazard data for 100% of the populated U.S. coast 6

7 California Coastal Analysis and Mapping Project Two Companion Large-Scale Efforts: Open Pacific Coast (OPC) Study San Francisco Bay Area Coastal (BAC) Study Re-study flood risk along the open coast and inland bays of all California coastal counties Re-map the elevation and inland extent of wave-induced coastal flooding 7

8 Presentation Outline Review of Coastal Hazards and Coastal Risk Review of the CCAMP/OPC Study, FIRM, and FEMA Regulatory Products Introduction to FEMA Flood Risk Products Concepts for Coastal Depth-Velocity Grids Benefits of Coastal Depth and Velocity Mapping Layers Coastal Depth and Velocity Profile Concepts Process-Based Runup Profile Development (Varying TWL Approach) Profile Influence on Constant TWL Approach Profile Influence on Varying TWL Approach Comparison of the Grid Mapping Results Recommendations 8

9 Review of Coastal Hazards and Coastal Risk Coastal hazards include large waves, high wave runup and overtopping, flooding, beach, dune, and bluff erosion, and tsunamis In California, El Niño winters ( , , ) are particularly hazardous Vulnerable areas of coastline are typically armored 9

10 Review of the CCAMP/OPC Study and FIRM The FIRM shows which areas are expected to flood during the 1-percentannual-chance event (i.e., the 100-year event) Highlights the inland extent of flooding (the flood zone boundaries) Does not provide detailed flood characteristics to the community 10

11 Coastal Flood Risk Products Flood Risk (Non-Regulatory) products supplement information on the FIRM. They provide additional flood risk data and information to help communities plan for resilience. Types of Flood Risk products: Flood Risk Map, Flood Risk Report, and Flood Risk Database Changes Since Last FIRM Areas of Mitigation Interest Increased Flooding Scenarios (BFE + 1 ft, BFE + 2 ft, BFE + 3ft ) Dune Size and Location Simplified Coastal Zones Flood Risk Assessment Data Flood Depth and Velocity Mapping Layers Coastal-Specific Flood Risk Datasets (FEMA, May 2014) 11

12 Coastal Depth and Velocity Mapping Layers - Concepts BakerAECOM was contracted by FEMA to develop coastal flood depth and velocity mapping layers for a pilot study area on the California coast Aptos, CA was selected for the pilot study Chosen because we have detailed CCAMP OPC Study data and results and several homes within the 1-percentannual-chance flood zone Community could benefit from mapping layers 12

13 Coastal Depth and Velocity Mapping Layers - Concepts An example of the beach and backshore in Aptos, California. 13

14 Coastal Depth and Velocity Mapping Layers - Concepts Pilot study area has many homes on the beach Some are protected by coastal protection structures Via Gaviota seawall and revetment 14

15 Coastal Depth and Velocity Mapping Layers - Benefits People and structures within a SFHA are vulnerable to multiple hazards including deep and fast-moving flood waters Structures can be subject to strong hydrodynamic forces which can damage structural members and potentially lead to collapse High water velocity can scour sediment and compromise building foundations 15

16 Coastal Depth and Velocity Mapping Layers - Benefits Coastal flood depth and velocity mapping layers provide detailed flood characteristics Help identify areas that might be subject to the greatest flooding and structures that might be most at risk (subject to greatest forces) Help communities identify safe areas and shelters during a coastal storm event, where depths and velocities are minimal 16

17 Coastal Depth and Velocity Mapping Layers - Benefits ASCE, USACE, and FEMA have developed flood depth and velocity metrics to characterize flood severity Metric Depth d Velocity V gd Depth x Velocity dv Depth x Velocity Squared dv 2 Characteristic Coastal Flood Depth Coastal Flood Velocity Hydrodynamic Force Hydrodynamic Force 17

18 Coastal Depth and Velocity Mapping Layers - Benefits Depth (d) Velocity (V) Force (dv or dv 2 ) Hydrodynamic forces can overturn walls, damage structural components, and scour foundations The forces are a function of both Depth (d) and Velocity (V) The forces can be approximated by Depth x Velocity (dv) and Depth x Velocity Squared (dv 2 ) 18

19 Coastal Depth and Velocity Mapping Layers - Benefits Flood Severity Category Depth Range (ft) Depth x Velocity Range (ft 2 /sec) Low < 0.5 < 2.2 Medium High Very High Extreme > 2.8 > 26.9 FEMA developed Flood Severity Categories for flood depth and velocity data Allow communities to readily identify areas that are most at risk 19

20 Coastal Depth and Velocity Mapping Layers - Example For the FIRM, a 1- D analysis transect was placed along each representative stretch of coastline The TWL was calculated for each transect The TWL was mapped as a single, constant BFE along each stretch of coastline 20

21 Coastal Depth and Velocity Mapping Layers - Example Coastal flood depths and velocities are then extrapolated along the beach to develop the Flood Risk mapping layers Flood Depth 21

22 Coastal Depth and Velocity Mapping Layers - Profiles Total Water Level = constant TWL mapped on FIRM Wave Runup Dynamic Water Level (DWL) Stillwater Level (SWL) Tide Level Surge Wave Setup Datum One potential method is to calculate depths and velocities using this constant TWL elevation Although TWL is constant, depths and velocities vary across the beach 22

23 Coastal Depth and Velocity Mapping Layers Profiles Constant Elevation Mapped on FIRM This approach has been applied along the east and Gulf coasts, where TWL are dominated by storm surge and are more constant This approach is problematic on west coast where TWL are dominated by wave setup and runup 23

24 Coastal Depth and Velocity Mapping Layers - Profiles Constant Elevation Mapped on FIRM TWL varies across beach and backshore This method overestimates depths and velocities across the beach Might be too conservative 24

25 Coastal Depth and Velocity Mapping Layers - Profiles Total Water Level = constant TWL mapped on FIRM Wave Runup Dynamic Water Level (DWL) Stillwater Level (SWL) Tide Level Surge In reality, TWL varies across the beach and backshore Another method is to use FEMA Guidelines equations to calculate the TWL up the beach and then calculate depths and velocities The method accurately captures TWL variation across beach Does not overestimate depths and velocities across beach BakerAECOM developed new analysis approach Wave Setup Datum 25

26 Process-Based Wave Runup Testing of Profile Development An example of the beach and backshore in Aptos, California. 26

27 Process-Based Wave Runup Testing of Profile Development Preliminary Base Flood Elevations (BFEs) for Aptos, California. 27

28 Process-Based Wave Runup Testing of Profile Development In the Varying TWL method, the varying water levels across the beach are calculated: SWL, StWL, DWL, TWL A flood elevation profile is developed across the beach along each transect line Flood depths and velocities are calculated from this flood elevation profile 28

29 Process-Based Wave Runup Testing of Profile Development CCAMP OPC Water Levels and Their Components Water Level SWL StWL DWL TWL Physical Components Astronomical Tides, Storm Surge, El Niño Processes SWL + ζ StWL + ξ (SWL + ζ + ξ) DWL +R (SWL + ζ + ξ + R) 29

30 Process-Based Wave Runup Testing of Profile Development The methodology requires the SWL, StWL, and DWL that correspond to the 1-percent-annual-chance TWL event at a particular transect. However, a response-based approach was utilized in the OPC Study such that only the 1-percent-annual-chance TWLs were directly calculated. Therefore, an approach was required to estimate the other TWL components. At each transect, a subset of TWL data was created consisting of the 50 annual maximum TWL events and their physical components (SWL, ζ, ξ, and R). 30

31 Process-Based Wave Runup Testing of Profile Development To determine the value of the other water levels, a procedure was implemented utilizing the subset of data: The averages of the SWLs, StWLs, and DWLs coinciding with the 50 annual maximum TWL events were calculated. The ratios of each of these averages to the average annual maximum TWL were calculated. The ratios were assumed to reflect the proportions of each water level to the overall TWL during the 1-percent-annual-chance TWL event. The ratios were applied to the 1-percent-annual-chance TWL to estimate the values of the SWL, StWL and DWL. Just as the 1-percent-annual-chance TWL represents the vertical extent of the TWL during the 1-percent-annual-chance event, the SWL, StWL, and DWL represent the vertical extents of these water levels during the 1-percent-annualchance TWL event. It was assumed that these values were valid at the shoreline. 31

32 Process-Based Wave Runup Testing of Profile Development Example: Calculated WSEs and depth profile (OPC Study Transect 66) 32

33 Coastal Depth and Velocity Mapping Layers - Comparisons Flood Elevation Constant TWL Flood Elevation Varying TWL 33

34 Coastal Flood Elevation Mapping Layers Detailed Comparison Flood Elevation Constant TWL Flood Elevation Varying TWL 34

35 Coastal Depth and Velocity Mapping Layers - Comparisons Flood Depth Constant TWL Flood Depth Varying TWL 35

36 Coastal Flood Depth Mapping Layers Detailed Comparison Flood Depth Constant TWL Flood Depth Varying TWL 36

37 Coastal Depth and Velocity Mapping Layers - Comparisons Flood Velocity Constant TWL Flood Velocity Varying TWL 37

38 Coastal Flood Velocity Mapping Layers Detailed Comparison Flood Velocity Constant TWL Flood Velocity Varying TWL 38

39 Coastal Depth and Velocity Mapping Layers - Comparisons Depth x Velocity Constant TWL Depth x Velocity Varying TWL 39

40 Coastal Depth x Velocity Mapping Layers Detailed Comparison Depth x Velocity Constant TWL Depth x Velocity Varying TWL 40

41 Coastal Depth and Velocity Mapping Layers - Comparisons Depth x Velocity Squared Constant TWL Depth x Velocity Squared Varying TWL 41

42 Coastal Depth and Velocity Mapping Layers - Concepts TWL With Multiple Return Periods X%-Annual-Chance TWL (ft NAVD88) Analysis Transect Backshore 50% (2-yr) 20% (5-yr) 10% (10-yr) 4% (25-yr) 2% (50-yr) 1% (100-yr) 0.2% (500-yr) 58 Beach + Bluff Beach + Bluff Beach + Seawall Beach + Bluff Beach Revetment + Beach Image sources: FEMA.gov 42

43 Summary and Recommendations Flood Risk products provide additional flood risk information to help communities plan for resilience Coastal flood depth and velocity mapping layers can alert communities about which areas and structures are most at risk during the 1-percent annual chance flood event ASCE, USACE, and FEMA have developed metrics and criteria to help communities interpret depth and velocity mapping layers There are two general approaches to develop these mapping layers: the Constant TWL and Varying TWL method Constant TWL method might overestimate flood depths and velocities Varying TWL method accounts for differences in coastal flood levels across the beach. More realistic and recommended by FEMA BakerAECOM has developed technical approach to produce mapping layers with the varying TWL 43

44 QUESTIONS? 44