TIDES & CURRENTS · The Art and Science of Tides & Tidal Current Prediction “Harmonic” Stations...
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T IDES & C URRENTS You don't paddle against the current, you paddle with it. And if you get good at it, you throw away the oars. Kris Kristofferson Time and tide wait for no man. Geoffrey Chaucer
Transcript of TIDES & CURRENTS · The Art and Science of Tides & Tidal Current Prediction “Harmonic” Stations...
TIDES & CURRENTS
You don't paddle against the current, you paddle with it. And if you get good at it,you throw away the oars.
Kris Kristofferson
Time and tide wait for no man.
Geoffrey Chaucer
Tides & Tidal Currents ?
Why?
What?
How ?
Where?
Who?
When?
Tides & Tidal Currents ?
Why do we care ?
What?
How ?
Where?
Who?
When?
Tidal Range
Tidal Current
Why We Care !
Paddling In Current
Tides & Tidal Currents ?
Why do we care ?
What causes the tides ?
How ?
Where?
Who?
When?
A Vector Diagram of Tidal Forces
Spring & Neap Tides
Making Sense of the Datums
MHHW (relative)
MLLW (relative)Slack (or “min before”)
Max Flood Current Max Ebb Current
Tide Cycles
An area has a semidiurnal tidal cycle if it experiences two high and two low tides of approximately equal size every lunar day. Many areas on the eastern coast of North America experience these tidal cycles.
An area has a diurnal tidal cycle if it experiences one high and one low tide every lunar day. Many areas in the Gulf of Mexico experience these types of tides.
An area has a mixed semidiurnal tidal cycle if it experiences two high and two low tides of different size every lunar day. Many areas on the western coast of North America experience these tidal cycles.
Datums (extracted) for 8665530, Charleston, Cooper River Entrance
5.76‘ relative
0‘ relative
Datums & References
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Tides & Tidal Currents ?
Why do we care?
What causes the tides?
How do they affect me as a paddler or small boater ?
Where are they different?
Who predicts them and how?
When are they not as predicted?
Rule of Twelfths (Relative to the Charleston Area)
1/12th 6”1st Hour
2/12ths 12”2nd Hour
3/12ths 18”3rd Hour
3/12ths 18”4th Hour
2/12ths 12”5th Hour
1/12th 6”6th Hour
Rules for Distance, Height, Speed
H=1
H=2
H=3
H=4
H=5
H=6
1 ft.
2 ft.
3 ft.
4ft.
5 ft.
6 ft.
1 NM 2 NM 3 NM 4 NM
Tides & Tidal Currents ?
Why do we care?
What causes the tides?
How do they affect me as a paddler or small boater ?
Where are they different?
Who?
When?
Everywhere!
Strange but True
Apogee vs Perigee
Tides & Tidal Currents ?
Why do we care?
What causes the tides?
How do they affect me as a paddler or small boater ?
Where are they different?
Who predicts them and how?
When?
The Art and Scienceof Tides & Tidal Current Prediction
“Harmonic” Stations Predictions Based on Tidal “Datums”
Computed with Harmonic Constituents
Measurements and Monitors
Local Monitoring at “Subordinate” Stations “Subordinate” are designed to adjust data to bays, inlets, estuaries,
rivers, and tidal basins based on real high/low measurements.
Long Term Accumulation of Data Epoch = 19 years (it takes 18.6 years to repeat the configurations of the
Earth-moon-sun system that generate the tides
Mathematical Interpolation “Smooths” the data for graphical and pictorial use
Predicting of Tides & CurrentsStep #1
“Harmonic” Station Prediction
CO-OPS ODIN (Interactive Map)
Table 1
Apps & Tables (various printed, PC & smart phone)
Logs
Annual Publications
Predicting of Tides & CurrentsStep #2
“Subordinate Station” Corrections
CO-OPS ODIN (Interactive Map)
Table 2
Apps & Tables (various printed, PC & smart phone)
Logs
Annual Publications
Predicting of Tides & CurrentsStep #3
Estimate Tide and Current Data Within Cycle
“Rules of Thumb” Tide Height: One-Rule of 12ths Current Speed: 50/90 Rule Drift: Rule of Thirds
Use Graphical Interpolation Table 3 Tide Logs
Putting It TogetherTidal Current Tables 2018Table 1.— Daily tide predictionsCharleston, Cooper River Entrance, SC,2018
Tidal Current Predictions 2018Table 1.— Daily current predictionsCharleston Harbor (off Fort Sumter), 2018
Using the Tools to go Places !
Tide Tables
Free
Tide Publications
Tide Logs
Tide “Apps”
NOAA CO-OPS
ODIN Website
https://tidesandcurrents.noaa.gov/
Lets go to Willtown Bluff on the N. Edisto River
Predicting of Tides & CurrentsStep #4
Understand Localized Effects
Inherent Current Offsets
Rotary Currents
Current Streams
Known Changes in Bathymetry
Documented Channel Restrictions
Local Knowledge & Notices
Tides & Tidal Currents ?
Why do we care?
What causes the tides?
How do they affect me as a paddler or small boater ?
Where are they different?
Who predicts them and how?
When are they not as predicted?
Predicting the Unpredictable
Localized Effects
Changes in Bathymetry, River Course
Undocumented Channel Restrictions
Weather Impacts
Wind
Local Precipitation
Floods (from hundreds of miles away!)
Drought
Barometric Pressure
Restrictions to tidal current and Bathymetry can have significant impact on tides.
Elliott Cut
Excessive Rain and the Resulting Floodcan have a significant impact on the tides.
October Flood 2015
Tides & Tidal Currents ?
Why do we care?
What causes the tides?
How do they affect me as a paddler or small boater ?
Where are they different?
Who predicts them and how?
When are they not as predicted?
Dumb Stuff !
