Tidal Datums, NAVD 88, and Coastal Commission Regs Curt Burfield, PLS Chief of Survey Standards Caltrans

How Did We Get Here? Governor’s Executive Order S 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 – 2011Guidance on Incorporating Sea Level Rise – 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

The National Geodetic Vertical Datum of 1929 is referenced to 26 tide gauges in the US and Canada 9

The North American Vertical Datum of 1988 is referenced to a single tide gauge in Canada 10

11

Gravity Recovery And Climate Experiment (GRACE) 12

NAVD 88 “Slope” 13

Tidal Datums Tide Gauges Tidal Benchmarks National Tidal Datum Epochs Datums

Essential 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

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)(CO-Ops)

Let’s Put It All Together Matching Tidal Datums to Orthometric Heights S.F. Golden Gate Datasheet and Tidal Bench MarkDatasheet Tidal Bench Mark

Datum Conversions Humbolt Bay- North SpitPrimary Tide Station Datums DatumsABBR.Tidal MetricTidal FeetNAVD88 MetricNAVD88 FEET Highest Observed Water LevelHOWL Mean Higher High WaterMHHW Mean High WaterMHW Mean Sea LevelMSL Mean Low WaterMLW North American Vertical DatumNAVD Mean Lower Low WaterMLLW Lowest Observed Water LevelLOWL

Then It Falls Apart Many Secondary and almost all Tertiary Stations Don’t have NAVD 88 Datums

Tide Stations Tide Stations Without NAVD 88 ElevationsNAVD 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 time Mean Lower Low Water (MLLW) Mean Sea Level (MSL) Orthometric Datums (Leveling) Related to the geoid Heights from differential leveling North American Vertical Datum 1988 (NAVD 88) Ellipsoidal (3-D) Datums (GPS) Related to an ellipsoidal model of the Earth Heights 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 EPOCH

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

How Did We Get Here? Governor’s Executive Order S 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 & Rahmstorf YearAverage of ModelsRange of Models in (18 cm)5-8 in (9-17 cm) in (36 cm)10-17 in (26-43 cm) 2070 Low23 in (59 cm)17-27 in (43-70 cm) Medium24 in (62 cm)18-29 in (46-74 cm) High27 in (69 cm)20-32 in (51-81 cm) 2100 Low40 in (97 cm)31-50 in ( cm) Medium47 in (121 cm)37-60 in ( cm) High55 in (140 cm) in ( 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 Projections TIME PERIODNORTH OF CAPE MENDOCINO SOUTH OF CAPE MENDOCINO to + 23 cm (-1.56 to 9 inches) 4 to 30 cm (1.56 to inches) to + 48 cm (-1.2 to inches) 12 to 61 cm (4.68 to 24 inches) to 143 cm (3.6 to inches) 42 to 167 cm (16.56 to inches)

Charting Sea Level Rise Projected Sea Level Rise - NAVD88 Metric North Spit DATUM min2030 max2050 min2050 max2100 min2100 max SLR HOWL2.590 MHHW MHW MSL MLW MLLW 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 / MHHW If 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 Owned Uplands State Owned Tidelands 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 MHHW MHW MLLW Importance of Shoreline Chart Datum

Maritime Boundaries AL, AK, CA, CT, FL, GA, MD, MS, NJ, NY, NC, NH, OR, RI, SC, WA Privately 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 MHHW MHW 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)