Hydrography - Tides & Water Level
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Why is knowing about tides important?
- -To reduce sounding data
- -Establishing vertical reference "below which water levels seldom fall"
- -Predict tides
- -Tidal current
Periodic vertical rise and fall of sea level due to gravity.
Define Tidal current/streams:
Periodic horizontal flow due to gravity.
What is a spring tide?
In phase (HW sun & HW moon)
What is a neap tide?
Out of phase (HW moon & LW sun)
What is Semi-diurnal?
Two LW's and two HW's spread uniformly over each lunar day.
What is Mixed, Semi-diurnal?
Two LW's and two HW's each lunar day that are different heights and spacing.
What is mixed, diurnal?
Sometimes two or one LW and HW spread unevenly over the lunar day.
What is Diurnal?
one LW and one HW each lunar day.
Non-tidal effects on water levels?
- -River outflow
What is LLWLT?
Level below which the tide seldom falls.
Datum transfer requirements?
- -Observe 3 or 4 days of HW & LW heights
- -Reference station should have similar tides
Installing Benchmarks Procedure:
- -Install minimum 3 BMs
- -Set on solid ground
- -install at HHWMT or above
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