217 217 217

200 200 200

255 255 255

0 0 0

163 163 163

131 132 122

239 65 53

110 135 120

112 92 56

62 102 130

102 56 48

130 120 111

237 237 237

80 119 27

252 174 .59

“The views, opinions and findings contained in this report are those of the authors(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by other official documentation.”

Heidi Moritz Portland District US Army Corps of Engineers Kate White Institute for Water Resources US Army Corps of Engineers

AWRA Annual Conference, November 15, 2016

EVALUATING THE MAGNITUDES, FREQUENCIES, AND EFFECTS OF COASTAL TOTAL WATER LEVELS

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USACE Climate Adaptation Policy: June 2011 Updated June 2014 To Reflect EO 13653

“It is the policy of USACE to integrate climate change preparedness and resilience planning and actions in all activities for the purpose of enhancing the resilience of our built and natural water-resource infrastructure and the effectiveness of our military support mission, and to reduce the potential vulnerabilities of that infrastructure and those missions to the effects of climate change and variability”

– Integrate best available and actionable climate science and climate change information at appropriate level of analysis into long-term planning, setting priorities, and making decisions

http://www.corpsclimate.us/adaptationpolicy.cfm

USACE Civil Works Program: Missions USACE operates, maintains, and manages more than $232B worth of the Nation’s water resource

infrastructure assets. Approximately 143,000 km of tidally influenced coastline.

Navigation: 926 coastal harbors & 40,200 km of waterways

Hydropower: 25% of nation’s hydropower

Flood Risk Management & Shore Protection: 14,000 km of levees & 640 km of shore protection

Ecosystem Restoration

Water Supply

Regulatory: (Wetlands / US Waters )

Recreation: 376 M visitors to USACE projects annually

Disaster Response

Beach Erosion, Nags Head, NC

Miami Beach Nourishment, FL )

Everglades

Dredge ESSAYONS ( Coos Bay, OR )

Bonneville II Powerhouse ( Washington )

Lake Seminole ( Mobile District )

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Stages of USACE Studies - require different types and detail of water levels to satisfy requirements at that stage.

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• Regional descriptions• Project level exposure

General Information and Scoping

• Components • Range of design variables• Influence on performance categories• Residual risk and robustness of alternative• Identify analysis tools for design

Feasibility

• Design calculations• Potential cost of project• Performance of project• Project Layout• Construction constraints

Design

• Comparison to original design• Measured data over performance life• Projections for maintenance requirements• Assessment of rehab or reauthorization

requirements• Identification of new data needed

Operation and Maintenance

General Outline – Total Water Level (TWL) Technical Letter

Principles - important to total water levels at projects

Breaking down the TWL into components

Regional, geomorphic, and temporal variability

Sources for water level information and cross shore zones

Projecting future conditions

Project specific analysis and assessment of total water levels

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How Did We Approach Things Before?

Assumed stationarity of water level estimates; with the resultant linear influence on processes and impacts.

Relied on historical data and events that may or may not provide the true risk of future water levels.

Focused on extreme water levels without looking at potential stability/performance effects of lower water level events, more frequent events, and longer duration events.

Over-reliance on model results has distanced the user from understanding dominant components and potential combinations at a range of frequencies.

Less emphasis on the possible limitations and thresholds of the receiving area.

Less awareness of the potential risk of selecting a water level at a given confidence interval. (mean value, 80%, 99% confidence)

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Principles: Total Water Level Components

Breaking a total water level down into the contributing components is essential to understanding risk and potential changes over time.

A project may have more than one controlling water level depending on the design and performance functions relevant to the project. (e.g. Navigation project: extreme water level for survivability of structure vs monthly mean for harbor operations)

The controlling water level may be the result of combinations of either coincident events or forcing/receiving area values. (storm surge impacting an inland area already stressed with interior flooding)

The controlling water level may be a value other than the extreme high or the extreme low. In addition, duration, frequency, and rate of change may be of importance to project performance and stability.

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Source: George McKillop, Eastern Region Headquarters, National Weather Service

Principles: Component Analysis and Use in Design and Performance Assessment

Data availability, data quality, and processing procedures may influence the accurate and complete description of the forcing and receiving climate.

The variability of other design or forcing parameters that are a function of water level may control the performance of the project.

Any description of water level components as well as influence on alternative performance is connected to a point in time described by the data and the processing assumptions.

Variability over increasing time scales from hours to decades of the relevant parameters may influence performance and adaptability of the range of project alternatives.

Analysis of total water levels is a separate activity from the selection of total water level values for design and project performance assessment.

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Coastal Total Water Level Components (All of these components operate on different frequency and time scales.)

Mean Sea Level (provides datum around which other components will vary; clearly impacted by climate change)

Tidal Range Non-tidal residual (any elevation change in the TWL not related to the astronomical tide)

(Be cautious about lumping these; different time scales, different systems and processes) – Seasonal cycle – Monthly mean sea level anomalies (low frequency anomalies, El Nino, etc.) – Storm surge (low frequency event) – Precipitation – River discharge

Wave-induced components – Wave setup and setdown – WL change due to infragravity and wave groups – Wave runup and swash (incident and infragravity contributions)

Amplification of Components by Topography (e.g. surge amplification)

Receiving Area Water Levels (ponding, tail-water elevations, etc.)

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Generic profile view schematic of total water level components. 11

Profile view schematic of ‘representative’ U.S. Gulf Coast geometry and associated influence on total water levels.

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Zones of Water Level Component Analysis – Data, Dominant Components, Component Interaction, Methods and Tools

Water level gauges often placed in the backshore for instrument protection.

(Random Seas and Design of Maritime Structures, Goda, 2010; Components of Storm-Induced Water Level along the Coastal Margin and Related Effects on the Nearshore Wave Environment, Moritz, 2007) 14

Contribution of Infragravity (or surf beat) to the Total Water Level

In some regions, this water level component can add as much as 1 to 2 meters to a total water level.

In threshold or extreme design conditions, this can be critical.

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A coastal riverine area illustrating the influence of rainfall and runoff discharge on sheltered coast total water levels.

Potential Component Combinations – Especially important in sheltered and interior areas

Consider How We Measure and Calculate TWL Components

What sources are we using/where is the data collected? (observations, modeling, etc.) Are all potential components captured?

If observations are being used, does the data processing capture all components? (infragravity may not be captured)

What assumptions are we making about concurrence or combinations, nonlinearity?

What values do we typically report on? (e.g. nonstationary TWL relative to a stationary project threshold)

How do we describe confidence intervals and extremes over time?

Extremes may vary on a different rate than sea level change.

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National map of regional mean sea level trends provides an overview of variations in the rates of relative local mean sea level observed at long-term tide stations (based on a minimum of 30 years of data. From NOAA CO-OPS http://tidesandcurrents.noaa.gov/sltrends/slrmap.html

Regional Variability - USACE projects are located in widely varying regions around the continental US, different water bodies as well as differences in topography.

Variability in Tidal Range on East Coast and Gulf Coast

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Characteristic tide curves near port facilities along the U.S. East and Gulf Coasts. The tides depicted are primarily semidiurnal along the East Coast, but diurnal at Pensacola. Both tidal cycle as well as projected typical range varies significantly.

0

5

10

15

20

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Sitka, AK 11/24/1999

Nawiliwili, HI 9/12/1992

San Francisco, CA 12/3/1983

Galveston, TX 9/13/2008

The Battery, NY 10/30/2012

Feet

Abo

ve M

SLWave Runup

Storm Surge

Average Monthly MSL Anomaly

Seasonal Cycle

Astronomical Tide

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Geomorphic Variability and Vertical Land Movement

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This figure from Kriebel, 2012, illustrates the effect of relative sea level rise on the depth of future flooding over a fixed Flood Stage threshold. Additional total water level components will amplify this WL difference over a fixed land datum.

Describe How Future Change in the Receiving Area may Impact Water Level – Erosion, dune elevation loss, interior changes

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Schematic of the components of TWL for a typical outer coast and sheltered /back bay.

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Identify the Project Water Level Frequency of Interest

Projects can be assessed in terms of both their stability against the design loading and their ability to perform their function under these loadings.

Performance Category

Process of Interest Frequency of Interest

Typical Return Period

Range of I t t

Extreme Low

Extreme High

Mean Range Duration Rate of Change

Threshold

Inundation short-term flooding high frequency 5 to 20 years X X X X

long-term flooding low frequency 20 to 500 years X X

Erosion short-term erosion high frequency 5 to 20 years X X X X

long-term erosionlow and high

frequency10 to 50 yrs X X X X

Wave Damage structure damage / stability

low frequency 50 to 100 yrs X X X X

Hydrostatic Loading differential loadinglow and high

frequency5 to 100 yrs X X X X X

Hydrodynamic Efficiency

system drainagelow and high

frequency5 to 50 yrs X X X X X X X

Operating Conditions

wave run-up, overtopping,

transmission, resonancehigh frequency 2 to 20 yrs X X X X X

Water Quality water quality high frequency 2 to 20 yrs X X X X X

USACE Total Water Levels of interest are not just 100 year extreme water levels.

Many projects will have multiple performance categories and multiple TWL’s of interest.

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Physical Process or Loading Condition Performance Function Potential Sea Level Rise (SLR), ftat a nearshore location where cast in terms of Low Value Intermediate Value High Value

PRESENT Wave action is depth-limited SLR-affected parameters 0.7 1.1 2.4 Depth-Limited Wave Height (H) due to SLR, ft

Present Depth-Limited Wave Height (H), ft = 6 Wave Hgt ~ Total Water Level + SLR 6.7 7.1 8.4 Relative Change in Performance Function due to SLR

Conventional Structure Stability (rigid) Hydrostatic Loading - Pressure Goda f(H) 12% 18% 40% Impulsive Loading (wave action) - Pressure Goda: f(H^2) 25% 40% 96%Compliant Structures (Armor Unit Stability) Direct Wave Action (armor unit weight) Hudson Equation: f(H^3) 39% 66% 174% Overtopping (wave action) - Volume USACE: f(H^1.5,exp^freeboard) 88% 152% 522% Lee-side Wave Action (armor unit weight) Van Gent: f(exp^H, exp^freeboard) 56% 95% 250%Nearshore and Structure Foundation Stability Foreshore Slope (rise/run) Kamphuis: f(H^-0.5) -5% -8% -15% Sediment Transport Potential (morphology change) Kamphuis: f(H^2) 25% 40% 96%Wave Run-up, Along Shoreface Run-up Distance USACE: f(H) 12% 18% 40% Run-up Speed USACE: f(H^0.5) 6% 9% 18% Run-up Depth (water depth increase) USACE: f(H) 12% 18% 40%

Example Summary of Water Level Influence on Stability or Performance Functions (using SLR as an example)

Source: Hans Moritz, Portland District

Summary and Key Questions

Based on the cross-shore zone location, can you describe your project exposure to TWL components?

Can you identify your limiting project characteristics? (thresholds, controlling design points, system interaction, etc.)

Have you identified if your project has more than one controlling water level and the primary components and frequency associated with each?

Have other WL parameters such as duration, frequency, and rate of change been fully described and evaluated?

Can you describe the expected accuracy and confidence of your water level estimates based on the data and method used?

Have the design and performance functions over the life of the project been described as a function of TWL change?

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USACE and NOAA Links

http://www.corpsclimate.us/rccslca.cfm

http://tidesandcurrents.noaa.gov/sltrends/sltrends.html

http://tidesandcurrents.noaa.gov/est/

Heidi.p.Moritz@usace.army.mil

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