tide prediction gis model for willapa bay

Mapping Predicted Tidal Exposure Durations Using a LIDAR-Based MLLW ReferencedTerrain Model

for Treatment and Controlof Spartina alterniflorain Willapa Bay, Washington

Coastal GeoTools ConferenceCoastal GeoTools ConferenceMyrtle Beach, South CarolinaMyrtle Beach, South CarolinaMarch 7-10, 2005March 7-10, 2005

Keven Bennett [email protected] Bennett [email protected] Alcock [email protected] Alcock [email protected] Wecker [email protected] Wecker [email protected]

University of Washington Olympic Natural Resources CenterUniversity of Washington Olympic Natural Resources Center

Willapa

BayWashington

State

ONRC campus in Forks, WAONRC campus in Forks, WA

University of Washington Olympic Natural Resources Center GIS

Created by the Washington State Legislature

Administered by the University of Washington

Providing researchand educationto supportecologicallysustainableforest and marineresourcesmanagement.

VancouverIsland, BC

Canada

WashingtonState

Photo byFritzi Grevstad

Nearly 1/3 of all viable fish and wildlife tide-flat habitat in Willapa Bay isinfested with Spartina alterniflora.

The bay supports shellfish andfin fisheries as well as the WillapaNational Wildlife Refuge.

At risk:biologicaldiversity,the local

economy…


Methods used to control the infestation:

Chemical Mechanical Biological


We use GIS for:

Bay-wide planning

Site-specific planning

Communication among stakeholdersAnd the public


Providing spatially explicit tide prediction mapsfor chemical treatment applications

Shows when, where and for how long plants will be exposed for treatments

Minimize treatment

impact

Optimize treatmentefficacy


Determining appropriate areas and times for chemical applications

Factors to consider:

Plant growth

Properties of Chemicals

Tides


Chemical Properties

Different chemicals need different minimum exposure times

Leaves must be drya certain amount

of time to give theherbicide time toaffect the plant

Plant Growth

Early seasonplants very short, treatment of plant low on tideflats more difficult

Late seasonplants much taller, treatment of plants low on tideflats much easier

Plant Growth and Chemical Properties


No fixed tide pattern Treatable areas change daily

Tides vary across the bayTidal timing variation can

be greater than 1 hour

Water level variation canbe greater than 3 feet

at any given time

Several different tide tables in useHistorical approximate fit

with local knowledge

No common tidal yardstick consistentwith NOAA NOS tide prediction sites

in Willapa Bay

Tides


Change vertical datum ofLIDAR derived terrain model

Terrain model datum is NAVD88

NOAA NOS Tide Predictionstations datum is MLLW(Mean Lower Lowest Water)

Adjust terrain model elevations toAdjust terrain model elevations toMLLWMLLW

This way, we can “flood” the terrainmodel using “water” whose surfaceis interpolated from NOAA NOS tideprediction stations.

Using a Common Elevation Datum toModel Tidal Prediction and Base Terrain Data


Referencing the Base Terrain Data

Tide Datums vary from location to locationTide Datums vary from location to locationOnly 4 stations in Willapa Bay haveOnly 4 stations in Willapa Bay have

NAVD88 elevationsNAVD88 elevationsrelative local MLLW datumrelative local MLLW datum

(NOS/NGS Leveling Data Points)(NOS/NGS Leveling Data Points)

Referencing the Base Terrain Data


We interpolated a correction grid basedon those 4 stations, which we thenused to adjust the LIDAR-derived

terrain model.


Nobeltec's Tides & Currents (T&C) software was found to be consistent with the NOAA NOS Tide Prediction Stations available online.

Query eachstationfor minimumwater levelfor the desiredexposuredurationon each day

The softwarealso tells uswhen thedesiredevent beginsat eachstation

Gathering Tide Prediction Data


1. Water Levels queried in T&Care saved to tables and integrated with points correspondingto the location of each station

Processing and Analyzing the Tide Predictionand Terrain Data

4. “Flood” the terrain model with “Flood” the terrain model withthe “water surface”the “water surface”

3. Overlay grid of Spartinaheights onto the terrain model

2. These points are used tointerpolate a “water surface”

Anything 18" above the water surface is exposed and treatable

for the desired duration.


1. Capture a water linewith a time and locationat each point using GPS

Each point on the water line is a point where the water's surface

intersects the terrain.

Validating the data

3. We assign this error value to

each GPS point, then

interpolate an error grid and

adjust the terrain model.

2. Compare the terrain

modelat each

location with a "surface“

representing the tide at each time.

Any difference is

an error.

Making this work possible:

US Fish and Wildlife Service – Willapa National Wildlife Refuge

Willapa Bay-Grays Harbor Oyster Growers Association

Coastal Resources Alliance

Pacific County

Washington State University

Pacific Coast Shellfish Growers Association

University of Washington

Pacific Conservation District

Washington State Department of Natural Resources

Washington State Department of Agriculture

Special Thanks to:

Charlie Stenvall, Jim Assenberg, Kim Patten,

Mark Scott, Kyle Murphy, Lester Mehrer, David Finlayson, Wendy Brown

Visit the Spartina website at www.onrc.washington.eduUniversity of Washington Olympic Natural Resources Center GIS

tide prediction gis model for willapa bay

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