Guidance for Conducting Wave Runup and Overtopping in a Coastal EnvironmentREBECCA AIKEN, STARR I I/STANTEC

JUNE 21, 2018

Wave Runup & Overtopping Guidance• Updated documentation providing the overarching logic and framework for coastal hazards due to wave runup and overtopping

• Contents:• Overview and Theory of Wave Runup and Overtopping

• Analytical Methods

• Mapping Application

• Documentation

• Draft guidance sponsored by FEMA and under review

Coastal Zones

Coastal ZonesWave runup and overtopping zones

Theory: Wave Runup•Wave runup (R) is the uprush of water from wave action on a beach or shore barrier such as a steep dune, bluff or coastal structure

•Runup is often the predominant flood risk in narrow floodplains

Wave HeightWave PeriodWave DirectionBarrier SlopeBarrier RoughnessErosion

Runup

Theory: Wave Runup

Theory: Wave Runup Theory

• Wave runup is often computed using empirical methods

• General Form:

𝑅

𝐻= 𝜉𝑎 + 𝑏

• Definitions:• R is the wave runup• H is the wave height• 𝜉 is the Iribarren Number• 𝑎 and 𝑏 are empirically derived coefficients

Theory: Wave Overtopping• If wave runup exceed the barrier crest, overtopping occurs

• Generates floodplains inland of steep coastal features

• Overtopping rate and volumes are computed using the EurOtopManual

Theory: Wave Overtopping

Source: https://nielsenhayden.com/makinglight/archives/014477.html

Analysis: Approach to Runup & Overtopping

Water Level &

Offshore Waves

Total Water Level

Total Water Level• Water Level

(Surge)• Setup, Runup and

Overtopping

Transect Analysis

Total Water Level

Analysis: Approach to Runup & Overtopping

Water Level &

Offshore Waves

Total Water Level

Total Water Level• Water Level

(Surge)• Setup, Runup and

Overtopping

Transect Analysis

Total Water Level

FEMA’s Guidance for Flood Risk Analysis and

Mapping: Wave Determination

Analysis: Transect Layout

• Wave runup and overtopping are sensitive to physical shoreline properties and wave characteristics, such as:

• Wave Parameters (H, T, and θ)

• Shoreline Setting

• Shoreline Slope

• Shoreline Surface Roughness

• Shore Barrier Height and Width

Analysis: Transect Layout

• Wave runup and overtopping are sensitive to physical shoreline properties and wave characteristics, such as:

• Wave Parameters (H, T, and θ)

• Shoreline Setting

• Shoreline Slope

• Shoreline Surface Roughness

• Shore Barrier Height and Width

Source: https://www.forward-now.com/2012/01/19/louisiana-coastal-restoration-spending-plan-proposed/

Analysis: Transect Layout

• Wave runup and overtopping are sensitive to physical shoreline properties and wave characteristics, such as:

• Wave Parameters (H, T, and θ)

• Shoreline Setting

• Shoreline Slope

• Shoreline Surface Roughness

• Shore Barrier Height and Width

Analysis: Transect Layout

• Wave runup and overtopping are sensitive to physical shoreline properties and wave characteristics, such as:

• Wave Parameters (H, T, and θ)

• Shoreline Setting

• Shoreline Slope

• Shoreline Surface Roughness

• Shore Barrier Height and WidthSources: https://www.pinterest.com/pin/326440672960846963/

https://mnfi.anr.msu.edu/communities/community.cfm?id=18985https://www.sandiego.org/explore/things-to-do/beaches-bays/carlsbad.aspxhttps://commons.wikimedia.org/wiki/File:Seawallventnor.jpg

Analysis: Transect Layout

• Wave runup and overtopping are sensitive to physical shoreline properties and wave characteristics, such as:

• Wave Parameters (H, T, and θ)

• Shoreline Setting

• Shoreline Slope

• Shoreline Surface Roughness

• Shore Barrier Height and Width

Analysis: Transect Layout

• Wave runup and overtopping are sensitive to physical shoreline properties and wave characteristics, such as:

• Wave Parameters (H, T, and θ)

• Shoreline Setting

• Shoreline Slope

• Shoreline Surface Roughness

• Shore Barrier Height and Width Steeper Slopes Greater Runup ElevationsSmoother Surfaces Greater Runup Elevations

Sources: http://www.hillblock.com/site/en/media/foto/detail/3.htmlhttp://www.kobelco.co.jp/english/engineering/

Analysis: Transect Layout

• Wave runup and overtopping are sensitive to physical shoreline properties and wave characteristics, such as:

• Wave Parameters (H, T, and θ)

• Shoreline Setting

• Shoreline Slope

• Shoreline Surface Roughness

• Shore Barrier Height and Width

Analysis: Transect Layout

• Wave runup and overtopping are sensitive to physical shoreline properties and wave characteristics, such as:

• Wave Parameters (H, T, and θ)

• Shoreline Setting

• Shoreline Slope

• Shoreline Surface Roughness

• Shore Barrier Height and Width

Source: http://www.dailyherald.com/article/20141031/news/141039518/

Analysis: Method Selection

• Runup is calculated through empirical methods

• General considerations and guidance are provided for typical coastal settings

• Guidance is provided to aid in the logic of method selection for common runup methods

Analysis: Runup MethodsRunup

Methods

Criteria

Slope Iribarren Number Shoreline Type

Emp

iric

al E

qu

atio

ns

TAW 1:8 to 1:1 0.5 - 8-10

Rock-Armored

Structures with

Narrow Surf Zones

Stockdon Up to 1:10 —Sandy Beaches

without Dune

Van Gent Up to 1:1 1 - 10

Impermeable

Structures Located in

the Surf Zone

SPM ∞ N/AVertical Walls (Sea

Walls and Bulkheads

Co

mp

ute

r M

od

els

ACES Up to 1:1

Up to 2 for Beaches

0.5 - 10 for Shore

Barriers

Beaches, Riprap, and

Impermeable

Structures

Runup 2.0 Up to 1:8 — Multiple Types

CSHORE N/A Greater than 0.3 Multiple Types

Analysis: Runup Method Selection

PROPRIETARY & CONFIDENTIAL TO STARR II (C) 2015-2016

Analysis: Overtopping

• Overtopping occurs when the runup elevation exceeds the barrier crest

• Overtopping Behaviors• Green Water• White Water

• EurOtop Manual calculates overtopping rates• Probabilistic (Mean)• Deterministic (Mean + 1 Std. Dev.)

• Possible to compute overtopping volumes for a shoreline reach

Sources: http://jmcoastal.co.uk/html/coastal-defences.htmlhttps://www.slideshare.net/shaileshshukla731/design-of-rubble-mound-seawall-48497527

Mapping: Runup and OvertoppingCoastal Flood Hazard Zones

• Zone VE: • Represents coastal high hazard

areas

• Wave runup ≥ 3ft above ground elevation

• BFEs are assigned

• Zone AE: • Wave runup < 3ft above ground

elevation

• BFEs are assigned

• Zone AH:• Ponding areas with 1-3 ft depths

• BFEs are assigned

• Zone AO: • Applied in areas of sheet-flow shallow

flooding

• Designated with depths of 1-, 2-, or 3-ft

• Zone Shaded-X: • Areas impacted by the 0.2-percent-annual-

chance event

Mapping: Runup and Overtopping

• Runup associated with narrow floodplains

• Larger floodplains observed when there is• Overtopping (AO, AH, or AE)• Structure Failure• Erosion

• Guidance provided to aid the Mapping Partner in mapping decisions• Decision Tree• FEMA’s Guidance for Flood Risk Analysis

and Mapping: Coastal Floodplain Mapping

Mapping: Runup and Overtopping

• Zone breaks are placed along the coast where the characteristics of the shoreline transition from one shore type to another

• Define the extents of each representative shoreline reach

Documentation

• Mapping Partner should document data, methods, and procedures applied during the analytical process• FEMA’s Guidance for Flood Risk Analysis and Mapping: Coastal Data Capture• FEMA’s Coastal Study Documentation and Intermediate Data Submittals

• Details on special considerations and approaches taken• Model Selection• Wave Characteristics• Structure Failure• Toe Scour• Statistical Considerations

Conclusions

• Updated wave runup and overtopping guidance

• Provide the Mapping Partner with tools for analytical and mapping decisions

• Draft document under review

Thank you! Questions?Rebecca.Aiken@stantec.com