Michael C. Nowlan, PE, CFM FMA Conference September 9, 2016 Building Community Resilience Through Action

Transcription

1 Michael C. Nowlan, PE, CFM FMA Conference September 9, 2016 Building Community Resilience Through Action

2 Resiliency Definition 1: The ability to become strong, healthy, or successful again after something bad happens Definition 2: The ability of something to return to its original shape after it has been pulled, stretched, pressed, bent, etc. We mostly deal with Definition 1, but 2 may have possibilities?

3 Management Impacts Resiliency A floodway is a management tool sizing minimum acceptable flood conveyance Floodplain management affects people by: Quantifying the hazard (accuracy) Defining permissible exposure (people/assets) to the hazard Sizing/configuration of facilities to protect people/assets Defining operation and maintenance of facilities (reliability)

4 Floodways and Resiliency? Removing floodplain storage may not promote resiliency. Older methods can miss peak flow increases due to changes in timing and attenuation Existing floodway definitions do not account for future development runoff characteristics upstream/downstream

5 Definition of a FEMA Floodway A regulatory floodway means the channel of a river or other watercourse and the adjacent land areas that must be preserved in order to discharge the base flood without cumulatively increasing the water surface elevation more than a designated height. ( Is it existing or future? Does it account for volume and timing for the entire river system?

6 Limiting Conveyance

7 How Did We Get Here?(History) Floodway as a planned flood corridor (before the NFIP) Red River diversion and Dallas levee corridor, TVA floodways NFIP defines 100 year floodplains Push back by property owners along waterways with NFIP floodplains NFIP allows floodways as a compromise, similar to today s Homeowners Flood Insurance Affordability Act

8 Classic Concept

9 FEMA Map?

10 Defining Floodways (Real World) Typically conveyance based analysis Steady state flow conditions with infinite volume A tool for communities to manage/regulate their floodplains Floodways can be changed The best we can do at the time?

11 Recent Re Examination Floodways Do we really need them? (presentations by TL Lovell in 2014 at TFMA and ASFPM conferences) 1992 Colleyville TX floodway implementation caused 25 42% increase in Q average increase in BFE Village Creek Case Study similar increases May 2013 ASFPM White Paper The Floodway Standard: Minimizing Cumulative Adverse Impacts April 2014 ASFPM/NAFSMA Unsteady and Two Dimensional Models: Issues for Regulatory Use 2014 NCTCOG/USACE Trinity River Corridor Development Preserving Valley Storage Questions have been building.

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13 Quotes from Texas (Bill Brown at the City of Arlington) A floodway is to hydraulics what the Rational Method is to hydrology They both were useful tools whose time has passed Them s fightin words!

14 Inspired Words Pictures are great, but they do not provide the whole picture Peaks have spectacular views, but it s all downhill from there. The flood will always find its own way, but we continue to give it new options. Yogi Bera was funny, except when he wasn t.

15 Yes! We Need (Better) Floodways Current floodway practices will not be eliminated without a better practice. FEMA still states floodways continue to be an effective tool in floodplain management. Development interests will not go away

16 Can FEMA Change? Archimedes is noted as saying, Give me a lever long enough and a fulcrum on which to place it, and I shall move the world

17 Can FEMA Change? Archimedes is noted as saying Give me a lever long enough and a fulcrum on which to place it, and I shall move the world Remember LAMP!

18 Potential False Premises with Yesterday s Floodways Local encroachment affects water surface elevations locally and not system wide Defining equitable encroachment is possible

19 Upstream/Downstream Connection

20 Floodway Implementation Issues How does one side of the river encroach first without adversely impacting property on the other side of the river?

21 Insert sketches

22 Floodway Implementation Issues How does one side of the river encroach first without adversely impacting property on the other side of the river? How does the floodway get defined upstream if downstream has established a narrow floodway? How does floodway get defined downstream if upstream has established a narrow floodway?

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24 Boundary Conditions/Assumptions Closed system or open system? Static system or dynamic system? 1D, 2D, 3D,.nD problem?

25 Boundary Conditions/Assumptions Closed system or open system? Static system or dynamic system? 1D, 2D, 3D,.nD problem?

26 Equitable Conveyance Variable Velocity Variable Flow Variable roughness Secondary channels

27 Equitable Conveyance (v and Q)

28 Light on the Horizon.

29 Floodways and Resiliency Abroad Floodway can mean an at grade road crossing for a creek in Australia s outback 2D modeling is being used to define Floodplain Development Zones Using velocity/depth product (VxD hazard is considered a combination of both) Future Development without a plan for the whole floodplain, development occurs ad hoc, and the cumulative effect of these developments is often not considered.

30 Management Landscape 2D dynamic flow modeling Growing recognition that volume and attenuation affect peak flow and stage More people and limited space Split flows/overflows through urban terrain paths. Decisions: preserving where the water goes now vs. deciding how/if we can safely steer it, or build near it.

31 Resiliency and Tolerance Small encroachment in large system was considered negligible in the past Today, some areas are moving towards no adverse impact, with hydro modification Additional runoff volume can be released, but only in a controlled fashion (no erosion). Today, small increments can be considered significant and can be cumulative. The threshold is going down.

32 Every Drop Creates a Ripple/Impact

33 What Can/Can t We Do? Regulate to the floodplain boundary? Advantages modeling/definition is done Disadvantages loss of perceived property value Redefine the floodway? Plan preserved conveyance corridors and preserved storage as a system. Include stakeholder input and make the mathematics secondary to planning decisions. Require more rigorous study for floodplain development approval in the floodplain fringe?

34 Recommendations Keep pre determined floodway lines and regulations (amnesty) Formulate a FWAMP (put up a better wall of defense) Demonstrate conveyance only is still adequate Evaluate velocity, volume and downstream impacts, and involve upstream and downstream stakeholders Formulate analysis to allow encroaching in fringe areas by mitigating volume displacement and peak flow/stage (police the wall )

35 Conclusions Resiliency becomes more difficult to achieve as we promote practices which move us closer to flooding As our understanding and ability grows so can our planning and execution (anvil/hammer vs. 3D printer) Change is hard Collaboration is harder Flood losses and litigation are more harder

36 Resiliency Through Action!

37 Questions?