March Urban Flood Risk Management

March Objectives Understand the Nature of Flooding & Flood Damage Alleviation Understand the Nature of Flooding & Flood Damage Alleviation Learn how to quantify expected annual damages for existing and future without project conditions and benefits for future with project conditions Learn how to quantify expected annual damages for existing and future without project conditions and benefits for future with project conditions Describe inventory procedures Describe inventory procedures Learn application of depth-damage functions Learn application of depth-damage functions

March Flood Control or Flood Damage Reduction or Flood Risk Management? Floods have occurred throughout time, and are not necessarily damaging Floods have occurred throughout time, and are not necessarily damaging Early legislation authorized “flood control” in response to devastating losses Early legislation authorized “flood control” in response to devastating losses We can’t really control floods, but we can modify water flows in space and time We can’t really control floods, but we can modify water flows in space and time Corps’ mission is reducing damages from floods, hence FDR Corps’ mission is reducing damages from floods, hence FDR

March Flood Damages = fn (Water + Development) through space and time Flood damage analysis integrates the hydro- and the economic to evaluate damage reduction alternatives

March Flood Risk Management Economic Analysis Helps answer the question “which proposed flood damage reduction plan is the best from an economic standpoint?” Helps answer the question “which proposed flood damage reduction plan is the best from an economic standpoint?” Evaluate the existing condition Evaluate the existing condition Evaluate the future without project condition Evaluate the future without project condition Analyze alternative damage reduction plans Analyze alternative damage reduction plans Compare plans using expected annual flood damage and flood damage reduction benefits Compare plans using expected annual flood damage and flood damage reduction benefits Since 1996, use risk analysis procedures Since 1996, use risk analysis procedures

March Hydrology and Hydraulics Hydrology and Hydraulics

March Types of Flooding River and stream overflow River and stream overflow Coastal Coastal Alluvial Alluvial Ponding Ponding Rising lakes Rising lakes

Damage Stage Discharge Frequency Discharge Stage Damage Frequency

Damage Frequency

March

Hydrologic Studies

Hydraulic Studies

March Economic Analysis Economic Analysis

March Computing Expected Flood Damages Three basic functions Three basic functions Discharge-probability Discharge-probability Stage-discharge Stage-discharge Stage-aggregated damage Stage-aggregated damage Derived functions Derived functions Stage-probability Stage-probability Damage-probability Damage-probability Integrate damage-probability to determine expected annual damage Integrate damage-probability to determine expected annual damage

March Risk Procedures Uncertainty in each function Uncertainty in each function Discharge-probability Discharge-probability Stage-discharge Stage-discharge Stage-damage Stage-damage Monte-Carlo simulation Monte-Carlo simulation Sample the 3 basic functions Sample the 3 basic functions

Risk Analysis Monte Carlo simulation is a numerical integration technique used to integrate the three functions to obtain EAD with the consideration of uncertainty. It does not add any information to the analysis but provides more information for decision makers.

March Existing and Future Without Project Damages 1. Delineate Affected Area 2. Determine Floodplain Characteristics Identify damage reaches Inventory land uses: Residential, Commercial, Industrial, Public, Others Estimate first floor elevations - uncertainty 3. Estimate structure/content values 4. Apply depth-damage curves

March Delineate Affected Area (Floodplain Outline)

March Damage Reaches

Inventory Land Uses Structure ID Location/address Structure value Content ratio Damage category n n Depth-Damage Function n First Floor Stage n Ground Stage n Coordinates n Stream Station Structure Inventory Data

March

March Apply Depth- Damage Functions

March Categories of Depth-damage functions used by the Corps of Engineers Basement or no basement Masonry, frame or adobe Slab or block foundation Basement living or storage area Raised on piers One story One and half story Split level Two or more stories Townhouse/condo

March Stage-Aggregated Damage Uncertainty First floor elevation First floor elevation Structure value Structure value Content value (content/structure value ratio) Content value (content/structure value ratio) “Other” value “Other” value Damage in depth-percent damage function Damage in depth-percent damage function

March Damage-Probability

March EXERCISE

March HEC – FLOOD DAMAGE ANALYSIS PACKAGE Developed by Hydrologic Engineering Center, Institute for Water Resources Developed by Hydrologic Engineering Center, Institute for Water Resources Integrates hydrology/hydraulics/economics in a single model. Integrates hydrology/hydraulics/economics in a single model. Multiple capabilities Multiple capabilities Incorporates risk analysis Incorporates risk analysis Documentation and training Documentation and training

March Flood Risk Management Alternatives Benefits for With Project Conditions

March Flood Risk Management Measures Structural measures Structural measures Modify flood behavior Modify flood behavior Dams and reservoirs, levees, walls, diversion channels, bridge modifications, channel alterations, pumping, and land treatment Dams and reservoirs, levees, walls, diversion channels, bridge modifications, channel alterations, pumping, and land treatment Nonstructural measures Nonstructural measures Modify damage susceptibility Modify damage susceptibility Flood warning and preparedness; Evacuation and relocation; Land use regulations; Flood proofing; Area renewal policies Flood warning and preparedness; Evacuation and relocation; Land use regulations; Flood proofing; Area renewal policies

March Evaluation of Without Project Condition

March Channel Modification

March Levee

March Non-Structural Measures

March Floodproofing Raising : most cost effective Raising : most cost effective Closures : good to 3 ft. Above ground Closures : good to 3 ft. Above ground Barriers: very expensive Barriers: very expensive

March Permanent Evacuation Value of vacant land in new use - residual flood damage Value of vacant land in new use - residual flood damage Reduction of damages Reduction of damages Adjust costs to avoid double-counting Adjust costs to avoid double-counting

March Identifying the NED Plan Without-project annual damages Without-project annual damages With project annual damages With project annual damages Annual benefits are damages reduced (without minus with) Annual benefits are damages reduced (without minus with) Annual net benefits are annual benefits minus annual costs Annual net benefits are annual benefits minus annual costs Compare across project scales and between alternatives to determine plan that yields greatest net annual NED benefits Compare across project scales and between alternatives to determine plan that yields greatest net annual NED benefits Decision-makers always have the final say Decision-makers always have the final say

March OTHER BENEFITS LOCATION BENEFITS LOCATION BENEFITS New activity moves into the protected floodplain New activity moves into the protected floodplain Benefits calculated as whichever is less of: Benefits calculated as whichever is less of: Increased potential damages in the changed land use assuming without project conditions; or Increased potential damages in the changed land use assuming without project conditions; or Cost of fill/flood proofing Cost of fill/flood proofing

March OTHER BENEFITS INTENSIFICATION BENEFITS INTENSIFICATION BENEFITS Existing activity is intensified Existing activity is intensified Benefits calculated as: Benefits calculated as: Increased income as a result of intensified activity Increased income as a result of intensified activity Increased land values Increased land values Computation of costs and revenues Computation of costs and revenues

March ECONOMIC ANALYSIS PLAN ANNUAL BENEFITS ANNUAL COSTS NET BENEFITS W/O Project 000 Plan 1 $500$350$150 Plan Plan Plan Plan

March SUMMARY The Corps’ mission in FRM is to contribute to reduce damages associated with floods. The Corps’ mission in FRM is to contribute to reduce damages associated with floods. Economic analysis of FRM alternatives helps identify the optimum plan (NED Plan) for implementation from a National economic perspective. Economic analysis of FRM alternatives helps identify the optimum plan (NED Plan) for implementation from a National economic perspective. Decision-makers always have the final say Decision-makers always have the final say Center of Expertise: South Pacific Division Center of Expertise: South Pacific Division