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Floodways, Do We Still Need Them? PowerPoint Presentation
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Floodways, Do We Still Need Them?

Floodways, Do We Still Need Them?

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Floodways, Do We Still Need Them?

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  1. Floodways, Do We Still Need Them? Presented at the TFMA Region 6 Inaugural Regional South Central Luncheon/Seminar- June 12, 2014, San Antonio, TX T. Lynn Lovell, PE, CFM, D.WRE – Halff Associates, Inc. Bill Brown, PE, City of Arlington, Tx John Ivey, PE, CFM – Halff Associates, Inc. Mike Moya, PE, CFM – Halff Associates, Inc.

  2. Outline of Presentation • Introduction – Reasons for Paper • Floodway Concept and History • Floodway Issues/ Impacts /Questions • Case Studies • Findings and Conclusions

  3. TFMA Spring Conference in Irving Joe F. J.B.. D. C. President and Vice-President of TFMA Frolic in Floodway Fringe

  4. Key Question of the Day: Is the continued use of the “Floodway Concept”, as a floodplain management tool, appropriate for sustainable, resilient, and prudent floodplain-related decisions and polices, now and in the future?

  5. Introduction – Reasons for Paper Lots Attention of Late: • ASFPM White Paper on “The Floodway Encroachment Standard: Minimizing Cumulative Adverse Impacts”Lulloff, et al, (May 2013) • ASFPM/NAFSMA Paper on Unsteady and Two Dimensional Models: Issues for Regulatory Use (April 2014) – Forum at Seattle last week.

  6. Introduction – Reasons for Paper Lots Attention of Late: • 2014 - Success of NCTCOG/Corps’ Trinity River Corridor Development Certificate (CDC) program in preserving “Valley Storage” along river

  7. Introduction – Reasons for Paper • Long time feeling that the floodway concept was not prudent floodplain management (since 1971) • Continued Trend: “Fill floodway fringe to the Limits”

  8. Introduction - WWBD Bill Brown has strong opinions regarding floodways: • A floodway is an administrative tool that has no physical meaning. • The concept is antiquatedand a historical tool whose usefulness is diminishing. • Becoming obsolete with modeling paradigm shift to dynamic models.

  9. Introduction - WWBD Bill Brown has stronger opinions regarding floodways (continued): • Floodways need to go away and we should focus on regulatory concepts where conveyance, zero rise, channel stability, and flood storage preservation are the primary factors in cases where encroachment is necessary. Otherwise, don’t encroach into the floodplain!

  10. Introduction - WWBD Bill Brown FINAL WORDS regarding floodways : • A floodway is to hydraulics what the Rational Method is to hydrology … • They both were useful tools whose time has passed. I sure wish he would make his OPINIONS clear on floodways!

  11. Introduction - WWBD Floodways Just Suck!

  12. Some Definitions THE REGULATORY FLOODWAY: The floodway is the channel of a stream, plus any adjacent floodplain areas, that must be kept free of encroachment so that the base flood (1% chance) can be carried without substantial increases (Max. of 1.0’ ) in flood heights. NO ADVERSE IMPACT : NAI is a philosophy that looks at the impacts of land use decisions, identifies adverse impacts, and mitigates them through a variety of actions.

  13. Some “No Adverse Impact” Floodway Factors • Encroachments within a floodplain or a stream, such as structures or fill, reduce the flood-carrying capacity, generally increase flood heights and velocities and often increase flood hazards in areas beyond the encroachment itself. • “FEMA Floodway fringe” encroachments have long been the cause of reduction of natural or existing valley storage (and changes in floods).

  14. The “Natural” Floodway Concept FLOODPLAIN LIMITS Discussed by Tom Lee, Wisconsin DWR, ASCE Paper, August 1971 FLOODWAY Essentially No Encroachment Into “MOVING WATER”

  15. The FEMA Floodway Concept Floodway Schematic (FEMA, 2012)

  16. The FEMA Floodway Concept Floodplain Equal Loss of Conveyance on Both Sides Conveyance is a function of Area, Wetted Perimeter, And Roughness Maximum 1.0’ Rise

  17. Floodway Regulations Current 8 States that enforce more restrictive floodways (state law): Illinois (0.1’) Montana (0.5’) Indiana (0.1’) Michigan (0.1’) New Jersey (0.2’) Colorado (0.5’) Minnesota (0.5) Wisconsin(0.01’)<<<

  18. Early TFMA Floodway Target Selection Discussion 1.0’ 0.5’ MINUS 1.0’ RISE!! 0.01’ +2.0’ RISE!!


  20. Flood Hazard Studies Timeline 1950 1960 1980 1970 1990 1960-1980 1950’s, 1960’s and early 1970’s 1960’s – 1970’s 1968 – 1980’s USACE Floodplain Information Reports (FPI’s) TVA Flood Hazard Information Studies Defined “Regional” and “Maximum Probable Floods” FIA – National Flood Insurance Study effort FHBM, FIS-FIRM, FBFM Flood Hazard Studies/ Flood Prone QUAD’s TVA, USACE, USGS, SCS 2000’s – MAP MOD and RISK MAP FLOODWAY CONCEPT/IMPLEMENTATION

  21. History • 1951 flooding in Kansas and Missouri resulted in a study to determine the feasibility of a flood insurance program. The study, funded by the insurance industry, did not favor such a program. • 1955 and 1956 floods resulted in Congress enacting the Federal Flood Insurance Act of 1956.

  22. History • Tennessee Valley Authority (TVA) – 1950’s First floodplain maps; first floodways • 1960 - Maryville, TN adopted the 1stFloodplain Ordinance with Floodway Map • FEMA Floodway Concepts, based on 1% Chance (100-year frequency) flood, since the early days of the NFIP

  23. History • 1950’s & 60’s TVA Flood Hazard Information studies defined “Regional” and Maximum Probable” floods • 1958 seven states (CN, IN, IO, MA, NJ, PA and WA) had enacted and were enforcing state floodplain management regulations • 1959 TVA report on reducing national flood damage

  24. History Housing and Urban Development Act of 1968 … gave birth to the NFIP and … “A Unified National Approach for Floodplain Management” The 1968 Act established floodplain and floodway regulations but community enforcement was voluntary

  25. History 1969 - The Water Resources Council revised the Flood Hazard Evaluation Guidelines and defined the floodway as we know it today.

  26. History – 1977 - EO 11988 “to provide for the discharge of the base flood so the cumulative increase in water surface elevation is no more than a designated amount(not to exceed one foot as set by the NFIP)” “to avoid to the extent possible the long and short term adverse impacts associated with the occupancy and modification of floodplains”.

  27. History – 1977 EO 11988 “Base flood is that flood which has a one percent chance of occurring in any given year” (also known as the 100-year flood) and “to provide for the discharge of the base flood so the cumulative increase in water surface elevation is no more than a designated amount (not to exceed one foot as set by the NFIP)”

  28. History - Floodway • James Goddard’s Report to the FIA 1978 “Origin & Rational of CriterionUsed in Designating Floodways”

  29. History - Goddard 1978 • The technical requirements must often be modified by practical, economic, social, and related considerations. (i.e. COMPROMISE!) • The “Zero” rise approach could result in inefficient use of the flood plain. (Was this a valid statement?)

  30. 1977 or 1978 Corps’ Floodway Study • Based on 2,390 cross-sections (Nation-wide) • Floodway Target was 1.0’ • Mean increase in water surface was about 0.7 foot. • Increase at many points was less than 0.4 foot. • Average width of floodway was about 55 percent of the 100-year flood plain width.

  31. Nine States with More Stringent Floodways (1978) • StateAllowable Rise (feet) • Illinois 0.1 • Indiana 0.1 • Maryland* Zero • Michigan 0.1 • Minnesota 0.5 • Montana 0.5 • New Jersey 0.2 • Ohio* 0.5 • Wisconsin 0.1 *Not in current list.

  32. History - Floodway Guidelines - 1979 • FIA published “The Floodway – A Guide for Community Permit Officials” HUD-529-FIA

  33. 1984 - Floodway Boundary “Cast in Stone” Once Floodways are designated by a community, usually when the FIRM is referenced by ordinance, floodways can only be changed by LOMC or FEMA’s remap efforts. (1984)

  34. 1987 – HEC Report to FIA “Floodway Concept Applications in Unique Situations” (Draft Report - February 1987) • Covered floodway concepts such as: • split flow, low levees, alluvial streams • Supercritical flow, developed floodways • Issues with bridges/culverts • Alternative methods of computation

  35. 2007 - ASFPM – “National Flood Programs and Policies in Review” • “A no-rise Floodway, with no impact on water surface and velocity should be required, so that only those areas of insignificant hydraulic conveyance could be filled.” • Paraphrase: “…Allowing current FEMA floodway standards (1’ Rise), causes increased flood peaks, additional flood damage, and promotes filling of riparian zones…”

  36. 2010 - Survey from ASFPM

  37. Floodway Issues, Impacts and Some Questions

  38. Regulatory and Economic Issues • Constitutional/Legal (taking issues) • Economics: Floodway fringe fill is a “Carrot” • Balance between Technical requirements and practical, economic, social, and environmental considerations (Remember Goddard’s quote, i.e. COMPROMISE).

  39. Technical Issues • Equity in encroachments allowed (equal loss of conveyance) • Depths and velocities at edges of encroachments (danger) • Existing development upstream, downstream • Other required permits (Sec 404, wetlands, unique, historic)

  40. Regulatory and Economic Issues • Public’s difficulty in understanding concepts • Costs for more detailed studies/floodway computations • Freeboard (Elevate fill and finished floors) • Political and land development pressures

  41. Technical Issues Islands

  42. Technical Issues Some Floodway Encroachments Mobile Homes in Floodway Bridges Levees/Treatment Plants

  43. Technical Issues • Adequate topographic mapping (accuracy and detail) • Effort/judgment needed for more intensive modeling of floodways • Unusual structures show up in floodways! Parking Lot Built Out Over Floodway

  44. Technical Issues • Urbanization of watersheds will eventually create higher flood elevations for floodways developed with “existing” conditions watersheds. (Old studies vs. New) • Complex flow patterns (i.e. split flow, diversions, etc.) create floodway difficulties • Delineated floodway on FEMA maps do not match hydraulic models (Map Mod saw this)

  45. The FEMA Floodway Concept HEC-2 STYLE

  46. A FEMA “Density Floodway” Concept (Circa 1981) Was this a good idea? Any Adverse Impacts here?

  47. The FEMA Floodway Concept HEC-RAS STYLE

  48. XPSWMM 2-D Floodway Technical Issues ? ? ?

  49. Questions: • “Do the economic benefits of additional development justify the physical encroachments of the floodway?” • “Does the floodway concept work in a changing paradigm of Unsteady and Two Dimensional hydrologic-hydraulic modeling?”

  50. Questions: • “Can a floodway-dominated stream achieve No Adverse Impact?” • Do we really need floodways in our floodplain management programs? • Is it realistic to think that the floodway concept can be eliminated?