Residual Water Level Calculator: Tidal Range and Design Water Level for a Quay or Retaining Wall
The design water level behind a port or quay wall.
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How this calculator works
Enter the highest and lowest water levels from the same datum.
Choose a gravity-type wall or a sheet pile-type wall.
The calculator gives the tidal range and the residual water level.
Formulas used
- H = HWL - LWL
- RWL = LWL + \frac{1}{3}H\ \text{(gravity wall)}
- RWL = LWL + \frac{2}{3}H\ \text{(sheet pile wall)}
Worked example
With the default numbers in the calculator above:
- Tidal range: 1.49 m
- Residual water level (RWL) for a gravity wall: 0.27 m
- For comparison, RWL for a sheet pile wall: 0.76 m
Change the numbers in the calculator to see the full working, every step, for your own case.
A second worked example
A different case, with these numbers: Type of wall Sheet pile-type wall: RWL = LWL + 2H / 3.
- Tidal range: 1.49 m
- Residual water level (RWL) for a sheet pile wall: 0.76 m
- For comparison, RWL for a gravity wall: 0.27 m
Common questions
What is the residual water level?
The level of water used in the design of a quay wall or retaining structure to account for the water pressure behind it. It is taken between one third and two thirds of the tidal range above the lowest water level.
Which fraction do I use?
One third of the tidal range for a gravity-type wall and two thirds for a sheet pile-type wall, as in the usual textbook method. Check the maritime design standard that applies to your project.
Why not use the highest water level?
The water behind the wall does not follow the tide completely, so the residual level is lower than the highest tide. Using it gives a more economical and realistic design.
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Got a question about this? Ask an engineering question and get a plain-language answer with references.
Further reading: Any port or harbour engineering text. In Australia, the maritime structures standard (AS 4997) applies.
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