Non Regulatory Risk MAP Products Flood Depth and Probability Grids

Non Regulatory Risk MAP Products Flood Depth and Probability Grids Virginia Floodplain Management Association 2015 Floodplain Management Workshop October 29th, 2015 Nabil Ghalayini, P.E., PMP, D.WRE, CFM Virginia DCR- Dam Safety and Floodplain Management nabil.ghalayini@dcr.virginia.gov 804-514-3884 1

Non Regulatory Risk MAP Products Flood Depth and Probability Grids Take a close look at flood non-regulatory depth and probability grids. Compare the non-regulatory grids to the regulatory Flood Insurance Rate Map (FIRM). Explore potential for informing local floodplain management and land use decisions. 2

Regulatory Products Non-Regulatory Products DFIRM Database Communities are required to adopt the FIRM and FIS as part of their local floodplain management ordinances. Communities are not required to adopt the non-regulatory products, but they are advised to use them 3

Non Regulatory Risk MAP Products Flood Depth and Probability Grids More clearly identify and depict high flood risk areas. Communicate how flood risk varies within the SFHA, and does not stop at a line on a floodplain map. Inform community planning, future development, risk reduction, and flood mitigation projects. Useful for flood hazard mitigation, recovery planning, disaster preparedness. Watershed based; multiple jurisdiction 4

FIS WSE profiles multi-frequencies 5

SFHA = Area that has 1% or greater chance of flooding in any given year. 1% chance at the boundary line, greater than 1% inside the boundary; how much greater? Need the probability grid. 6

risk = function (hazard; probability; exposure) flood hazard indicators: flood maximum depth, flood wave height; velocities ---> depth grids, velocity grids probability of occurrence; % chance ---> probability grids exposure: vulnerable populations, activities, structures 7

Flood Depth and Probability Grids Derived from the same elevation data and hydrologic models used for developing regulatory products: Calculated water surface elevation profiles (typically 10, 4, 2, 1 and 0.2 percent annual chance flood events) Topography (typically DEM or DTM, derived from LiDAR) Provide more nuanced information: WSE grid Ground Elevation grid = Depth grid (provides depth of flood variation) Multiple WSE profiles; topography >> Percent annual chance of flooding probability grid 8

Flood Depth Grids FIRM 1% Annual Chance (100-yr) Floodplain 1% Annual Chance Depth Grid Each grid cell has a flood depth value based on the computed flood water surface elevation and the LiDAR derived topographic data. (e.g. darker shade = greater flood depths.) Provides numerical values of flood depths at any location. 9

1% Depth (100-Year) 4.7 ft 0.0 ft 0.1 ft 10

1% Depth (100-Year) 4.7 ft 0.0 ft 0.1 ft 11

10% Depth (10-Year) 1.5 ft 1% Annual Chance Floodplain Boundary 0.0 ft 0.0 ft 12

4% Depth (25-Year) 2.8 ft 0.0 ft 0.0 ft 13

2% Depth (50-Year) 3.8 ft 0.0 ft 0.0 ft 14

0.2% Depth (500-Year) 8.9 ft 1.7 ft 4.3 ft 15

1% Depth (100-Year) 4.7 ft 0.0 ft 0.1 ft 16

Percent Annual Chance Probability Grid (Not provided to all communities) FIRM 1% Annual Chance (100-yr) Floodplain Percent Annual Chance Probability Grid SFHA = Area that has 1% or greater chance of flooding in any given year. 1% chance at the boundary line, greater than 1% inside the boundary; how much greater? Need the probability grid. The probability of flooding in any given year is provided for each grid cell. Darker colors represent higher probability. May be derived from the regulatory multiple flood profile H&H results and DTM. 18

Percent Annual Chance of Flooding 10% + 0.4% 1%

30-Year Percent Chance Grid (Not provided to all communities) Compounds the percent annual chance of flooding over the 30-year life of a typical mortgage. 1% annual chance (SFHA boundary) over 30 years is equivalent to : [1-(1-0.01)^30] = 0.26 or 26% at the SFHA boundary line Inside SFHA boundary: (10% >> 96%) 50 years: Inside SFHA boundary: (10% >> 99%) Probability of a location being flooded during the life of a 30-year mortgage. Informing an owner with a 30-year mortgage on a structure in the floodplain that the structure site has a 26 percent or greater chance of flooding during the life of the mortgage is generally more effective than stating that the structure is in a 1-percentannual-chance floodplain. 20

Percent Chance of Flooding over a 30-yr Period 96% + 11% 26% 21

Quiz If a development site is located within the SFHA (a.k.a. 100-year floodplain), True or false? A. There is a 1% chance that the site will flood in any given year. B. The site will flood once every 100 years. C. There is more than 25% chance that the site will flood during the next 30-years. 22

Quiz If a development site is located within the SFHA (a.k.a. 100-year floodplain), True or false? A. There is a 1% chance that the site will flood in any given year. False. By definition, it is 1% or greater annual chance. Could be much higher than 1%, depending on location and terrain. B. The site will flood once every 100 years. C. There is more than 25% chance that the site will flood during the next 30-years. 23

Quiz If a development site is located within the SFHA (a.k.a. 100-year floodplain), True or false? A. There is a 1% chance that the site will flood in any given year. False. By definition, it is 1% or greater annual chance. Could be much higher than 1%, depending on location and terrain. B. The site will flood once every 100 years. False. The site has a 1% or greater chance of flooding in any given year. But it could flood multiple times. C. There is more than 25% chance that the site will flood during the next 30-years. 24

Quiz If a development site is located within the SFHA (a.k.a. 100-year floodplain), True or false? A. There is a 1% chance that the site will flood in any given year. False. By definition, it is 1% or greater annual chance. Could be much higher than 1%, depending on location and terrain. B. The site will flood once every 100 years. False. The site has a 1% or greater chance of flooding in any given year. But it could flood multiple times. C. There is more than 25% chance that the site will flood during the next 30-years. True 25

Flood Depth and Analysis Grids Engineering data is rendered to visually communicate risk more effectively, based on multiple parameters: probability, depth, velocity, etc.. Help visualize variations in the hazard (severity) and risk (probability) of flood beyond the one percent or greater annual chance in the SFHA. High risk areas visually stand out (islands, flooded access roads) Can easily inform land use planning (e.g. emergency access), location of critical facilities, advance recovery planning, and emergency preparedness. Helps local officials identify and prioritize potential areas for mitigation based on potential for damage to property, traffic disruption, road closures, etc Provide numerical data input to flood damage estimates (strong correlation between flood damage and flood depths). Provide data input to benefit-cost analyses to help evaluate cost effectiveness of potential mitigation projects. 26

Flood Risk Assessment Provides estimates of potential losses associated with structures in a SFHA. Average Annualized Loss ($/year) by 2010 census block based on the Hazus AAL Study. May include loss due to damage to structures, contents, and business disruption. Improves ability to identify areas requiring higher building code standards or flood-resilient designs and materials. Supports mitigation plan updates and disaster recovery planning through improved risk quantification, and identification of vulnerable structures and populations. Refined Flood Risk Assessment: User-defined facilities data (Hazus Level 2) can be used to refine building and contents losses when local data is available. 27

Flood Risk Assessment AAL, HAZUS, TEIF, other 28

Flood Risk Assessment Census Blocks symbolized with Risk Assessment Data Dollar Losses Residential Loss Commercial Loss Other Asset Loss Percent Damage Evaluates Building Stock Structure and Content Considerations Business Disruption Considers Total Occupancy Tables Considers Lost Income and Wages 29

Flood Risk Assessment 30

Areas of Mitigation Interest 31

Areas of Mitigation Interest Identifies areas that may benefit from increased local awareness and/or enhanced mitigation plans. Based primarily on data in local mitigation plans provided by the community, H&H study results and flood insurance claims. Identifies areas at risk of flooding, along with the factors that contribute to those risks Useful in formulating building code enhancements, prioritizing mitigation actions, and identifying needed resources Raise awareness by local stakeholders of areas within and upstream of the watershed that may be contributing to flood risk and associated interrelationships 32

Areas of Mitigation Interest Examples Dams / Levees / Flood control structures (dam break inundation zones; hazard classification change due to development) Stream flow pinch points (upstream flooding; roadway overtopping) Repetitive loss hotspots (from past flood insurance claims) Known flood prone areas that are not identified on the FIRM Emergency routes overtopped Critical facilities at risk / isolated (WWTP / hospital) Areas of significant erosion (incl. coastal structures) Areas downstream of significant watershed changes (altered hydrology; loss of floodplain storage) 33

Flood Risk Map Watershed-based high-level flood risk overview. Contains results of Risk MAP project non-regulatory datasets. Identifies flood risk hot spots for community consideration. Depicts flood risk data from FRA and AOMI across jurisdictions. Promotes coordination between neighboring upstream and downstream communities within the same watershed. Includes composite total 1-percent-annual-chance loss per census block. Available in ANSI E-Size 34 in x 44 in hardcopy Communities may create customized versions of the FRM from within the FRD. 34

Flood Risk Report High-level summary of flood risk for either a single watershed or the project area that may be included in a mitigation plan. Summarizes flood risk data that can be used for outreach, and for risk and vulnerability assessments in mitigation plans. Detailed flood risk information on specific areas. Helps prioritize mitigation actions and resources. 35

Non-Regulatory Risk MAP Products Flood Risk Database (includes flood risk datasets) Changes Since Last FIRM (CSLF) Flood Depth and Analysis Grids Flood Risk Assessment (FRA) Areas of Mitigation Interest (AOMI) Flood Risk Report (FRR) Flood Risk Map (FRM) 36

Possible Risk MAP Datasets Note: Not all datasets are produced with every map revision. Changes Since Last FIRM Horizontal changes in flood zones Structure/Population counts impacted by change Depth & Analysis Grids Flood depth (10, 04, 02, 01, 0.2 percent chance) Percent Annual Chance grid (based on the 5 standard freq) Percent 30-Year Chance Grid Water Surface Elevation (multi-freq) Water Surface Elevation Change (1%, vertical CSLF) Velocity Grids Multi Freq Grids for Coastal Areas, etc. 1% plus flood depth (upper confidence limit; or future conditions, riverine) Hillshade Flood Risk Assessment Average Annualized Loss 2010 Refined Flood Risk Assessment Hazus or Non-Hazus with improved data/assumptions Areas of Mitigation Interest 37

Previous New Mapping (w/ LiDAR) Zone A Zone X Zone AE Zone X Waterloo 39

New Mapping 40

Changes Since Last FIRM Unchanged Unchanged SFHA Increase SFHA Increase SFHA Decrease Unchanged 41

Changes Since Last FIRM (CSLF) Depicts increases and decreases in floodplain and floodway boundaries and flood zone designations since the previous FIRM. Contributes to more transparency in the map change process. Provides property owners with a visual for easy understanding of how they may be affected by the map changes. The CLSF is produced only if the previous FIRM is digital, or if the mapped area is not shown on the previous FIRM. Optional Structure/Population counts impacted by change. Helps community officials easily identify properties affected by the map change using GIS. 42

Changes Since Last FIRM (CSLF) Virginia Notification Requirement Section 15.2-976 of the Code of Virginia requires communities to notify affected property owners individually; public notices are not sufficient. 15.2-976. Notification of changes to the Federal Emergency Management Agency Special Flood Hazard Area map. Any locality receiving notification from the United States Federal Emergency Management Agency (FEMA) that a change in the FEMA Special Flood Hazard Area map concerns or relates to real property within such locality shall provide to each owner of any such property (i) written notification that such change has occurred within that locality and (ii) written notification of the website, address, and telephone number for the National Flood Insurance Program to aid the property owner in determining if there has been a change to the flood risk of the property. Notice sent by bulk or first class mail to the last known address of such owner as shown on the current real estate tax assessment books or current real estate tax assessment records shall be deemed adequate compliance with this requirement. 43