HEC-FDAFlood Damage Reduction Analysis

Pete AndrysiakSources:•HEC-FDA Users Manual Version 1.0 Jan 1998•Metropolitan region of Louisville, Kentucky Study of Beargrass Creek Basin Final Feasibility Report-Volume 1•Metropolitan region of Louisville, Kentucky Study of Beargrass Creek Basin Final Feasibility Report-Volume 2•COL Harry Spear, Commander Louisville District•Jeffery G. Kleckner, Planning Division Chief•Neil O’Leary, Economist

Objective

•Take the Hydrologic Engineering Center's Flood Damage Analysis (HEC-FDA) computer program and become familiar with its capabilities.

• Use a completed study, the Louisville District's experiences in conducting a risk-based analysis of flood damage reduction alternatives for the Bear Grass Creek, basin in Metropolitan Louisville, Kentucky.

HEC-FDAWhat is it?

• a next generation Flood Damage Analysis computer program for formulating and evaluating flood damage reduction plans.

• streamlines the study process following functional elements of a study involving coordinated study layout, hydrologic engineering analysis, economic analysis, and plan formulation and evaluation.

HEC-FDAWhat Does it do?

• Quantifies uncertainty in discharge-frequency, stage-discharge, geotechnical levee failure, stage-damage functions

• Incorporates these uncertainties into economic and performance analyses of alternative flood damage reduction plans.

• Evaluates plans by expected annual damage associated with a given analysis year or the equivalent annual damage over the project life of the plan.

• Provides Information on the flood risk performance in the results. • Provides output tables and selected graphics of information by plan,

analysis year, stream, and damage reach for the plan. • Compares results of the various plans Windows NT and 95, and Unix-based computer operating systems.

Where to Begin• Provide structure, many key players and elements that need to be

brought together

• No portion can be done in a vacuum

• Proposed Structure (Decision Making Process)

– Pick the Study Team

– Define the problem and focus team for analysis

– Conduct thorough analysis (each Team Member)

• gather facts

• develop logical assumptions

• present to team and manager

• focus plan development

• develop goals and objectives

– Develop Courses of Action

– Analyze and Compare Courses of Action

– Decide

Pick the Study Team• Louisville District Staff w/expertise in plan formulation• Economics, engineering, cost estimating, real estate, and construction• Local groups

– Jefferson County Metropolitan Sewer District (MSD) sponsor and team member

– Kentucky Department of Fish and Wildlife Resources (KDFWR)– Beargrass Task Force appointed by Mayor of Louisville

• Government Officials with diverse backgrounds

• Educational Institutions

• Businesses

• Industry

• Non-profit Organizations

purpose to firmly establish the role of the creek in meeting the needs of the community in future recreation, education, and green space; to protect the cultural and natural heritage associated with the creek

• Federal– U.S. Fish and Wildlife Service (USFWS) IAW provisions of Wildlife

Coordination Act

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Define the ProblemFocus Team for Analysis

Beargrass CreekBackground

• Development in the last two decades, particularly in the upper reaches of South Fork has resulted in additional rainfall run-off, and a corresponding increase in potential damage

• Flooding caused by locally intense rainstorms. Flood waters from the streams generally rise rapidly, with little warning time, and have high velocities. In the upper reaches of the South Fork, the duration of flooding is generally between 25-45 minutes, once the water is out of bank. Expected depths of flooding on first floors of structures for a 1% chance event range up to 8.5' on South Fork and on Buechel Branch.

• Approximately 85% of the structures are residential. • A 1% chance flood event along the South Fork would damage

759 structures, valued at $219,123,000, and would result in about $45,590,000 in damages.

• On Buechel Branch, a 1% chance flood would affect about 170 structures valued at $15,286,000, and would cause damage estimated at $2,812,000.

• A 10% chance flood would cause an estimated $6,803,000 in total damages on South Fork, and $890,000 on Buechel Branch.

Beargrass Creek Background

Define Damage Reaches• Damage reaches are spatial floodplain areas. • Used to define consistent data for plan evaluations and to

aggregate structure and other potential flood inundation damage information by stage of flooding.

• Defined by the beginning and ending stations (river mile, kilometer, etc.) along the stream and can extend into the floodplain to include the largest flood deemed reasonably possible.

Thorough AnalysisUsing FDA by Hydro Guy

• The HEC-FDA program requires specific water surface profiles for the 50-, 20-, 10-, 4-, 2-, I-, .50-, and .20- percent chance exceedance frequency flood events

• For the above probabilities the returns periods are 2, 5, 10, 25, 50, 100, 250, and 500 years respectively.

• The profile data are normally imported from stream hydraulics programs such as the HEC River Analysis System package (HEC-RAS) or HEC 2 in this case

Exceedance Probability with Uncertainty

Stage-Discharge Uncertainty

Study Structure Occupancy Types

Depth Percent Damage

Econ Guy’s Nightmare

Structure Inventory Data

Stage Damage Function at IndexWith Uncertainty

Develop Planning Objectives

• Develop an array of alternatives, both structural and nonstructural, that will alleviate out-of-bank flooding problems

• Preserve or protect natural, cultural, and historical resources • Work with local sponsor (MSD), taking into account their goals

and considerations, and ID their goals and considerations, ID the NED plan, as well as the locally preferred plan if applicable

• Evaluate opportunities for environmental restoration that improve the aquatic and terrestrial habitat conditions

• ID a plan that will meet environmental, social, and economic criteria and is sound from an engineering standpoint

Develop Courses of Action

• Facts are presented to Study Team• Team develops alternative plans which consist of one

or more flood damage reduction measures and actions– Reservoirs– Detention Basins– Channelization– Levees and Floodwalls– Bridge Improvements– Nonstructural Measures– Combinations

Flood Reduction Measure Selection

The Process• Screen out benefit/cost ratio of < 1• Next take the measure that provides greatest net benefits using

incremental analysis• Team identified a problem

National Economic Development Plan

• Consisted of 10 components:– 8 detention basins– I-wall/earth levee– section of channel modification

Recalculate Hydro data for plans

Levee Height

Compare Courses of ActionEvaluation of Plans by Year

Compute expected probability function to get 5 percent or less residualdamage associated with a .01 exceedance probability event

EvaluationEquivalent Annual Damage

The damage value associated with the without- or with-project condition over the life of the project considering changes in hydrology, hydraulics, and economic conditions over the life. Expected annual damage is computed for each year and discounted topresented worth which is annualized to obtain the equivalent annual damage value. Rather than compute the expected annual damage for each year, it is computed for base year and most likely future year, and interpolated for other years. The years beyond the most likely future year are assumed equal to the most likely future year.

Equivalent Annual Damage

Expected Annual Damage

The integral of the damage-probability function. In risk-based analysis it is equal to the average or mean of all possible values of damage determined by exhaustive Monte Carlo sampling of discharge-exceedance probability, stage-discharge, and stage-damage relationships and their associated uncertainties.

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Project Performance

Stage associated with start ofsignificant damage

Probability of target stage being exceededin 10-, 25, and 50- year period

The chance of containing the specific .10, .04-,.02-, .01-, .004-, and .002- exceedance probability within the stage, should that event occur

The Bottom Line

•EAD reduced 69% from$3,015,000 to937,000•314 structure removedfrom 1.0% chance floodplane•Remaining structure receive considerable protection•more frequent or shallowerdepths of flooding

What is Next?

• GIS-based calculation of flood likelihood and damage at each location

• Risk-based flood plain boundary zone

NEW!!HEC-FDA 1.1

Questions?