Tidal Datums, NAVD 88, and Coastal Commission Regs

Curt Burfield, PLS

Chief of Survey StandardsCaltrans

How Did We Get Here? Governor’s Executive Order S-13-08

Nov. 14, 2008 The California Resources Agency… shall

request that the National Academy of Sciences (NAS) convene an independent panel to complete the first California Sea Level Rise Assessment Report

The Business, Transportation, and Housing Agency shall … prepare a report within 90 days of release of this Order to assess vulnerability of transportation systems to sea level rise…

The $64,000 Question Caltrans’

Guidance on Incorporating Sea Level Rise – 2011 1. Request information from District

Surveys to evaluate existing vertical elevation data and benchmarks to determine the correlation between current sea level and planned facility elevations…

Outline Geodetic Datums Tidal Datums Tidal Stations and Data Sheets Matching Datums Using Tide

Stations VDatum (NOS Software) Sea Level Rise

Geodetic vs. Tidal datums Geodetic Datums

• Defined by mathematical model of earth• Used to measure positions (lat., long.,

height) Tidal Datums

• Defined by tide phases (MSL, MLLW, etc.)• Used to measure local water levels and

depths (bathymetry) • Used to establish certain horizontal water

boundaries

Orthometric Heights*

* Everything you wanted to know about vertical datums

but were afraid to ask

9

The National Geodetic Vertical Datum of

1929 is referenced to 26 tide gauges in the

US and Canada

10

The North American Vertical Datum of 1988 is referenced to a

single tide gauge in Canada

11

12

Gravity Recovery And Climate Experiment (GRACE)

13

NAVD 88 “Slope”

Tidal Datums

Tide Gauges Tidal Benchmarks National Tidal Datum

Epochs Datums

NWLON StationsEssential Equipment

• Automatic water level sensor• Backup water level sensor• Backup & Primary data collection platform• Protective well• Shelter• Solar Panel• GOES satellite radios• Telephone modem• Ancillary geophysical instruments• System of Bench Marks

• Data Collection Platform• Acoustic or pressure sensor• Solar Panel• GOES Transmitter

Short term stations

Control Stations

• Water Level• Wind Speed/Direction• Barometric Pressure• Air/Water Temp.• Conductivity/Temp• Chart Datum• Tsunami/Storm Surge

Observations Collected

15

6A specific 19 year period that includes the longest periodic tidal variations caused by the astronomic tide-producing forces.

6Averages out long term seasonal meteorological, hydrologic, and oceanographic fluctuations.

6 Provides a nationally consistent tidal datum network (bench marks) by accounting for seasonal and apparent

environmental trends in sea level that affects the accuracy of tidal datums.

6The NWLON provides the data required to maintain the epoch and make primary and secondary determinations of tidal datums.

NATIONAL TIDAL DATUM EPOCH

Types of Tides

Mixed Tide

Semidiurnal Tide

Diurnal Tide

MHHW

Tidal Datums Station Datum: Unique to each water

level station - Established at a lower elevation than the water is ever expected to reach. - Referenced to the primary bench mark at the station- Held constant regardless of changes to the water level gauge or tide staff MHHW: Mean Higher High Water The average height of the higher high

water of each tidal day observed over the NTDE MHW: Mean High Water

The average of all the high water heights observed over the NTDE

MTL: Mean Tide Level The arithmetic mean of mean high water

and mean low water MSL: Mean Sea Level or LMSL: Local

Mean Sea Level The arithmetic mean of HOURLY heights

observed over the NTDE MLW: Mean Low Water The average of all the low water heights

observed over the NTDE MLLW: Mean Lower Low Water The average of the lower low water

height of each tidal day observed over the NTDE

GT: Great Diurnal Range The difference in height between mean

higher high water and mean lower low water

Higher High Water

20

Tide Station Data Online

Center for Operational Oceanographic Products and

Services (CO-Ops)

Let’s Put It All Together

Matching Tidal Datums to Orthometric Heights

S.F. Golden Gate Datasheet and Tidal Bench Mark

Datum ConversionsHumbolt Bay- North Spit Primary Tide Station Datums

Datums ABBR. Tidal Metric Tidal Feet NAVD88 Metric NAVD88 FEET

Highest Observed Water Level HOWL 2.693 8.84 2.590 8.50

Mean Higher High Water MHHW 2.090 6.86 1.987 6.52

Mean High Water MHW 1.874 6.15 1.771 5.81

Mean Sea Level MSL 1.129 3.70 1.026 3.37

Mean Low Water MLW 0.384 1.26 0.281 0.92North American Vertical Datum NAVD88 0.103 0.34 0.000 0.00

Mean Lower Low Water MLLW 0.000 0.00 -0.103 -0.34

Lowest Observed Water Level LOWL -0.883 -2.90 -0.986 -3.23

Then It Falls Apart Many

Secondary and almost all Tertiary Stations Don’t have NAVD 88 Datums

Tide Stations Without NAVD 88 Elevations

VDatum – Where Land and Sea Meet

Vertical Datums - 3 height systems

A surface to which heights are referred.

Tidal Datums (Tide Stations)Defined by observation of tidal variations over a

specified epoch of timeMean Lower Low Water (MLLW)Mean Sea Level (MSL)

Orthometric Datums (Leveling)Related to the geoidHeights from differential leveling

North American Vertical Datum 1988 (NAVD 88)

Ellipsoidal (3-D) Datums (GPS)Related to an ellipsoidal model of the EarthHeights directly from GPS

North American Datum 1983 (NAD 83)

VDatum Conversions Horizontal Between NAD 27 – NAD

83-ITRF – WGS 84 Vertical Between NGVD29 and

NAVD88 using VERTCON Vertical Between NAD 83 and

NAVD 88 using GEOID 12A, or earlier geoids

Tidal Datums for CONUS and PR, VI

SEA LEVEL RISE – Its Real!- Sort of…

IDEALIZED CHANGE OF TIDAL EPOCH

1983-01 EPOCH

RELATIVE SEA LEVEL CHANGE AT SEVERAL LOCATIONS IN THE U.S.

How Did We Get Here? Governor’s Executive Order S-13-08

The California Resources Agency… shall request that the National Academy of Sciences (NAS) convene an independent panel to complete the first California Sea Level Rise Assessment Report

The Business, Transportation, and Housing Agency shall … prepare a report within 90 days of release of this Order to assess vulnerability of transportation systems to sea level rise…

Vermeer & RahmstorfYear Average of Models Range of Models

2030 7 in (18 cm) 5-8 in (9-17 cm)

2050 14 in (36 cm) 10-17 in (26-43 cm)

2070

Low 23 in (59 cm) 17-27 in (43-70 cm)

Medium 24 in (62 cm) 18-29 in (46-74 cm)

High 27 in (69 cm) 20-32 in (51-81 cm)

2100

Low 40 in (97 cm) 31-50 in (78-128 cm)

Medium 47 in (121 cm) 37-60 in (95-152 cm)

High 55 in (140 cm) 43-69 in (110-176 cm)

Tectonic Shifts

This is from the NAS report. The San Andreas Fault runs up the California Coast, and heads out to sea at Cape Mendocino. South of the Cape, Sea levels are rising, but north of the Cape, The land is rising, and sea levels dropping.

NRC SLR ProjectionsTIME PERIOD NORTH OF CAPE

MENDOCINOSOUTH OF CAPE

MENDOCINO

2000-2030 -4 to + 23 cm (-1.56 to 9 inches)

4 to 30 cm (1.56 to 11.76

inches)

2000-2050-3 to + 48 cm(-1.2 to 18.84

inches)

12 to 61 cm(4.68 to 24 inches)

2000-2100 10 to 143 cm(3.6 to 56.28 inches)

42 to 167 cm(16.56 to 65.76

inches)

Charting Sea Level RiseProjected Sea Level Rise - NAVD88 Metric North Spit

DATUM 2000 2030 min 2030 max 2050 min 2050 max 2100 min 2100 max

SLR +0.0 -0.04 0.23 -0.03 0.48 0.10 1.43

HOWL 2.590

MHHW 1.987 1.947 2.217 1.957 2.467 2.087 3.417

MHW 1.771 1.731 2.001 1.741 2.251 1.871 3.201

MSL 1.026 0.986 1.256 0.996 1.506 1.126 2.456

MLW 0.281 0.241 0.511 0.251 0.761 0.381 1.711

MLLW -0.103 -0.143 0.127 -0.133 0.377 -0.003 1.327

LOWL -0.986

CCC Draft SLR Steps At Least 2 scenarios-

a low and high rise 1. Establish SLR

Range for Project 2. Determine how

impacts from SLR affect the site

3. Determine how the project will impact coastal resources

4. Identify Project design alternatives to minimize impacts

5. Finalize Design and Submit Coastal Development Permit (CDP)

Step 1 Establish Project SLR Define Expected life of Project Determine Existing Tidal Elevations Determine expected ranges of SLR Will local geology influence SLR?

Geologic Uplifts (Tectonic) Subsidence (water over drafting or

oil extraction)

Step 2 Determine Impacts Apply SLR scenarios to projects

site For large areas, NOAA Lidar Data is

acceptable for DTM Erosion (Engineers) Flooding and Inundation

Tipping Point Other (Groundwater)

How Accurate are the Maps?

The Tipping Point

Analysis of MLLW / MHHWIf Short term Project –

Minimal SLR Long Term Project No Tipping Point within

Project lifespan Tipping point within

Project lifespan

Then No Further Evaluation

More Work Submit findings to

Planners Submit findings,

including expected dates – More Work

Questions

AL, AK, CA, CT, FL, GA, LA, MD, MS, NJ, NY, NC, OR, RI, SC, WA

Privately OwnedUplands

State OwnedTidelands

Territorial Seas

State Submerged Lands

Contiguous Zone

Exclusive Economic Zone

Federal Submerged Lands

High Seas

Privately Owned

State Owned

TX

3 n. mi.

12 n. mi.

200 n. mi.

Privately Owned

State Owned

DE, MA, ME, NH, PA, VA

MHHWMHW

MLLW

Importance of Shoreline

Chart Datum

Maritime BoundariesAL, AK, CA, CT, FL, GA, MD, MS, NJ, NY, NC, NH, OR, RI,

SC, WAPrivately Owned

Uplands

State Owned

Tidelands

Territorial Sea

State Submerged Lands

Contiguous Zone

Outer Continental Shelf

High Seas

Privately Owned

State Owned

HI, LA, TX

3 n. mi.*12 n. mi.

200 n. mi.

Privately Owned

State Owned

DE, MA, ME, PA, VA

MHHWMHW

MLLW Chart Datum

24 n. mi.

* TX, the Gulf Coast of FL, and Puerto Rico claim submerged lands to 3 marine leagues or 9 n. mi

Exclusive Economic Zone (international)US EEZ

(fisheries)