Datums and Tides Mean Low Tide versus Mean Lower Low Water And
the winner is.!
Slide 4
The following slide is taken directly from the NOAA/TCOON web
sites pages that gives the official relationships for the various
Sea Level Datums (Mean Sea Level and its various statistical
offsets) and the Land (Terrestrial) Datums (NAVD88 and Mean Low
Tide) for the Rainbow Bridge on the Neches River Channel. This
location has been chosen because it is one of the (currently) few
NOAA tide gauge sites for which data is available in real time on
the internet, and has published the relationship between the Sea
and Terrestrial datums. One thing should be borne in mind. Mean Sea
Level changes both by location around the coastline of the U.S. and
over long periods of time. The relationships at the Rainbow Bridge
do NOT hold true anywhere else - although the differences MAY be
minor.
Slide 5
Courtesy TCOON Web Site The relationships shown here are given
reference to an arbitrary station datum. Following slides have
changed this to make things relative to Mean Low Low Water via high
level math (addition and subtraction!!) See slide #12 and #13 for
definitions of these datums. NAVD 88 elevation updated 5/2013,
stated accuracy is 0.028m (about 1 inch). These datums are marked
preliminary until the 2013 levels are run.
Slide 6
Slide 7
Confused? Lets Try an Example!
Slide 8
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NOAA Tides & Currents Web Page
Slide 10
Slide 11
SIMPLE! Take two aspirin and call 713-690-4626, ask for Chris
or Mike and have your credit card ready! Just joking about the
credit card!
Slide 12
The following are provided for reference purposes - if you are
feeling bold.
R2Sonic 2024Odom MB-1 Reson 7125 Geoacoustics Geoswath Edgetech
4600 Swath/Sidescan And new 2020 Why Multibeam?
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Slide 22
Bottom Elevation Contour Chart (Multibeam) Example #1
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Slide 24
Bottom Elevation Contour Chart (Single Beam) Survey Lines
(Single Beam) Channel Centerline Dock Face
Slide 25
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Bottom Elevation Surface Chart (Multibeam)
Slide 27
Example #2
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Slide 30
Multibeam Surveys are faster to execute, especially for larger
areas and in the case of busy docks. They give 100% bottom coverage
(single beam surveys at 50 feet spacing give only 28%!) The data
can still be sectioned and volumes calculated by the average end
area method but we can now also use a full terrain modelling
approach. New system can beam-steer and look up under docks, moored
barges or shallow draft vessels (depending on space between the
hull and bottom) Some systems also provide sidescan sonar type
imagery from the amplitude returns (not as good as a specialist
sidescan sonar but no co-location issues) More expensive than
single beam (30 to 50%) Data takes longer to edit and produce final
deliverables
