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Aching Joint Probability? – Diagnosing Your Options for Interior Drainage Behind Levees for Compliance with 65.10 (A Reviewer’s Perspective) William Zung, PMP, CFM Anish Pradhananga, PE, CFM Rick Nusz, PG, PH, CFM ASFPM 2013 Conference June 12, 2013
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Transcript of Aching Joint Probability? – Diagnosing Your Options for ... · PDF fileAching Joint...

  • Aching Joint Probability? Diagnosing Your Options for Interior Drainage Behind Levees for Compliance with 65.10 (A Reviewers Perspective) William Zung, PMP, CFM Anish Pradhananga, PE, CFM Rick Nusz, PG, PH, CFM ASFPM 2013 Conference June 12, 2013

  • Agenda

    Levees in NFIP

    65.10 Overview

    Interior Drainage Analysis

    Diagnosis

  • Levees in NFIP

    Levee A man-made structure, usually an earthen embankment, designed and constructed in accordance with sound engineering practices to contain, control, or divert the flow of water so as to provide protection from temporary flooding.

    44 CFR 65.10 establishes the criteria for levee systems to meet to be accredited on FIRMs

    Accredited Levee A levee shown on the FIRM as providing protection from the 1-percent-annual-chance flood.

  • Levees in NFIP

    Interior Area USACE EM 1110-2-1413 defines as the area protected from direct riverine, lake, or tidal flooding by levees, floodwalls, or seawalls and low depressions or natural sinks.

    Coincident Events two events occurring together

    Joint Probability The probability of two events occurring together.

  • Levees in NFIP Coincident Events

    Source: HEC SSP Users Manual

    Exterior needs, Variable B : Stream Gage data or Hydraulic Study

    Interior needs, Variable A : Stream Gage data or Rainfall Runoff

    models with synthetic storms Variable C : Hydraulic model with varying outlet

    conditions

  • Levees in NFIP

    Initiation

    Study initiated and identify levees Levee ownership and background research PAL eligible / Accredit / Not Accredit

    PAL

    PAL Meeting Progress Reports 65.10

    Mapping

    Accredit on FIRM Not Accredit on FIRM (Levee Analysis and

    Mapping Process)

  • 65.10 Overview

    65.10 - Structural (b1) Freeboard

    (b2) Closures

    (b3) Embankment Protection

    (b4) Foundation Stability

    (b5) Settlement

    (b6) Interior Drainage

    (b7) Other

    65.10 Non Structural

    (a) General

    (c) Operation

    (d) Maintenance

    (e) Other

  • 65.10 Overview

    www.fema.gov/living-levees-its-shared-responsibility/fema-levee-resources-library

  • 65.10 Overview Reviewers Perspective

    PM 63 Completeness Check

    Submittal Includes all Elements

    Signed by a PE Checklist breaking down

    each element Tab Submittal Detailed Review of

    Interior Drainage Analysis

  • 65.10 Overview Reviewers Perspective The submitting P.E. is responsible

    for the technical content Old can still be good

    Check submittal for completeness to comply with all 65.10 criteria

    Friendly coordination with submitter to resolve questions

    We will check for consistencybut make it easy to find

  • 65.10 Overview Reviewers Perspective Digital submittals are preferred over

    volumes of hard copies Rely heavily on the summary report

    to tell us the answer

  • 65.10 Overview Reviewers Perspective

    65.10(b)(6) Interior Flooding Interior Flooding Analysis submitted? Coincidental Peak Analysis done? Pump station operation included in the

    analysis? Data certified by a Professional

    Engineer?

  • 65.10 Overview Reviewers Perspective 65.10(b)(6) Interior Flooding

    Areas of Interior Flooding Identified?

    Site map showing areas of interior flooding mapped?

    Base Flood Elevations shown on areas with greater than 1 foot of flooding?

  • 65.10 Overview Reviewers Perspective 65.10(c) Operation Plans and Criteria

    Operation Plan submitted? Are closure devices addressed in

    Operation Plan? Is the interior drainage system (including

    flood warning system) addressed in Operation Plan?

    Periodic Inspection and operation stated?

    Operations Plan formally adopted as per criteria in 65.10(c)?

  • 65.10 Overview Reviewers Perspective Common Errors

    Not using Joint Probability Analysis Documentation is inconsistent

    Pumps in model do not have the same parameters as documented in the Operation Plan.

    Number of closures in Interior Analysis do not match the number on the As-Builts and do not match the number in the O&M plans

    Not using the 1% annual chance Many times the design event for interior flooding is more

    frequent than the 1% (e.g. 4% [25yr])

  • Interior Drainage Analysis What are you symptoms?

    Rainfall Runoff analysis of interior drainage area Data availability Interior and Exterior measurements

    Stream gage data Precipitation gages Existing detailed flood study on exterior or interior

    Multiple uses of this study than just 65.10 Capital Improvement Planning

    Engineering Judgment Risk justify the analysis

    Simple Complex

  • Interior Drainage Analysis What are you symptoms?

    Risk justify the analysis Heavy Industrial with storm water pipe network Agricultural with open channels

  • Interior Drainage Analysis What are my options?

    A. USACE EM 1110-2-1413 has two general methods to perform the hydrologic analysis in interior areas 1. Continuous Record Analysis Method

    a. Period of record b. Discrete events of historic record c. Stochastically generated continuous record

    2. Coincident Frequency Method: Weighted frequency relationship developed from probabilities of exterior and coincident interior stage condition

    B. American Association of State Highway and Transportation Officials (AASHTO)

    C. The Worst Case Scenario

  • Interior Drainage Analysis A.1.a. Period of record method Estimates the interior runoff hydrograph for a

    period of historic precipitation. Period of record exterior stage hydrograph at

    desired location. Need stream data as well as interior rainfall

    data. The process preserves the, seasonality,

    persistence and dependence or independence of exterior and interior events.

    Key Features: Gages Historic Interior

    and Exterior Lots of Data Preserves

    Seasonality

    Simple Complex

  • Interior Drainage Analysis A.1.b. Multiple Discrete Event method

    Generates composite stage- frequency function by analyzing two conditions. 1. Selected high exterior events that have on

    effect on interior flooding with coincident historic interior rainfall.

    2. Selected low exterior events associated with interior flood generated by coincident historic interior rainfall or hypothetical frequency storms. The joint probability theorem is applied to combine these two functions to generate a composite function.

    Joint Probability Theorem P= P(A)+ P(B) For Partial Duration series P= P(A)+P(B)-P(A)xP(B) For annual Series

    Key Features: Gages Interior Flooding

    with High Exterior Interior Flooding

    with Low Exterior Joint Probability

    Theorem

    Simple Complex

  • Interior Drainage Analysis A.1.c. Stochastic Method

    Generate synthetic sequences from the historic record

    Accounts for the randomness of events Overcome the limitation due to short period of

    records.

    Key Features: Can be analyzed

    with synthetic sequences

    Recorded Data limitation is avoided

    Randomness of events are represented

    Simple Complex

  • Interior Drainage Analysis B: Coincident Frequency Method

    Hydrologic and Hydraulic modeling Uses synthetic events Frequency event is known

    Applies Total Probability Theorem to generate stage-frequency function

    P(A) = probability of exceeding a given interior ponding elevation

    P(Bi) = probability river is at specific stage interval (i) P(A/Bi) = probability of exceeding a given pond

    elevation if the river stage is at the stage interval (i)

    P(A)= P ABi

    X P(Bi)

    =1

    Key Features: Can be analyzed

    with synthetic sequences

    Recorded Data limitation is avoided

    Randomness of events are represented

    Simple Complex

  • Interior Drainage Analysis Coincident Frequency Method cont.

    HEC-SSP

    Interior stages (ft) P(A/Bi)

    Exterior stages (ft) P(Bi)

    1-percent-annual-chance joint probability water surface elevation P(A)

  • Interior Drainage Analysis A.2. Coincident Frequency Method HEC SSP

    Coincident Frequency Plot HEC SSP will perform the

    Coincident frequency Analysis and generate a frequency curve

    474.44

  • Interior Drainage Analysis B. American Association of State Highway and Transportation Officials (AASHTO) Joint probabilities of design

    coincident stream flows at confluences.

    Coincident frequencies based on watershed Area Ratio

    Alternative approach for interior areas with very limited data

    Use the higher result of the two scenarios

    Simple Complex

  • Interior Drainage Analysis C. Assume the Worst Case

    All gates closed Pump Stations operate per O&M Plan 1-percent-annual-chance rainfall on watershed Duration of 24 hours

    Pros

    Easy to Calculate

    Cons

    The event likely will have less than 1-percent-annual-chance in any given year

    The inundation area may be larger than 1-percent-annual-chance event

    Simple Complex

  • Diagnosis

    Consider your symptoms What is at Risk Agricultural fields, industrial, homes, etc. What impacts of the inter