Coastal wave measurement

Coastal wave measurement

Wave propagation in coastal areas is heavily influenced by land formations and shoaling effects. For this reason, wave statistics cannot easily be predicted from numerical models, and direct measurements of wave height and direction are required. It is easy for buoys and other measuring methods to be vandalized, hit by ships or thrown ashore during storms. In coastal areas, the best alternative is a system that is below the surface, out of harm’s way.


Highlights

  • Reliable statistical estimates
  • High accuracy, independent of depth
  • Monitoring both wind waves and swell

What and why

What is coastal wave measurement and why is it useful?

Measurements of the physical characteristics of waves are most useful when the wave data is collected over long periods. Individual, extraordinary waves, such as transient waves generated by passing boats, may not be representative of the area, so taking wave measurements over a longer period enables the establishment of a clear pattern and detailed underlying data that can be used as the basis to provide sound advice on coastal management.

Long-term measurements can analyze the impact of wave patterns on harbors and other coastal structures and formations, for example. They can also help prepare for safe execution of operations at sea that depend on stable sea conditions, such as loading and unloading from supply ships to offshore installations.

Who it's for

Scientists are those typically most interested in coastal wave measurement, when investigating coastal processes, such as sediment transport and activities outside/inside harbors, or even biological processes.

Wave data is an important input for their research, as it is one of the most important parameters influencing such processes. This data can help uncover clear correlations between cause and effect, and secure precision in scientific research.

Study of the nutritional uptake and growth rate of mussels on the coast provides a good example of a biological process influenced by the wave regime. Mussels depend for their well-being on exposure to a continuous flow of nutrient-rich sea water, and wave activity is crucial to this flow.

Marine construction engineers need to know about the forces that will affect the structures they are designing and building, such as breakwaters, offshore wind turbines, docks and piers. Such structures are affected by wind and currents, but waves will usually exert the greatest force.

The ability to document the biggest wave forces likely to affect a structure is key for engineers. This helps determine its dimensions and the choice of construction materials. Determining the average or characteristic wave field is also important, as this repetitive force influences structural fatigue.

The desired end result for marine construction engineers is usually to design a safe, durable structure that is as compact and lean as possible. 

Technical considerations

Before initiating coastal wave measurements, there are two main questions that need to be answered:

First, what is the water depth in the area to be measured?

Second, what is the assumed wave state, or what types of waves will most likely be found in the area of focus? Areas that are protected by island archipelagos and reefs have shorter and smaller waves, whereas areas exposed to the open ocean have longer and larger waves.

Data presentation

Nortek can help you process your wave data, either internally in the instrument to generate online data or on a PC if you have a data set collected and recorded in the instrument.

Processing entire data sets after the completion of measurement provides a more complete picture of wave behavior during the deployment period.

Processing data in real time may help operators execute their marine operations in an informed and safe manner, based on continuous information on the state of waves and the sea.

Choice of instrument

Nortek has invested considerable effort in responding to the above-mentioned challenges, and provides wave measurement solutions that produce high-quality data both for engineering projects and in coastal process studies.

Wave height, wave period and wave direction are the three parameters that are the most relevant for measurement.

Nortek’s technology offers the ability to measure all of these parameters in most types of wave fields. Our instruments can provide precise measurements across the entire spectrum of conditions.

Nortek offers four instruments that are useful for coastal wave measurements:

The Vector is the appropriate instrument for measuring waves in less than 3 m water depth, especially in physically confined areas or when capturing rapid velocity fluctuations is desired.

The Aquadopp can be used if measuring waves in less than 5 m water depth – and a cost-efficient and straightforward solution – is required.

The Aquadopp Profiler helps you measure waves in less than 10 m water depth, and also gives you the ability to measure current profiles simultaneously.

Instruments in the AWAC and Signature series are the best instruments for waves at water depths of 5–100 m, as these are able to measure wave motion directly at the water surface. By contrast, the three instruments mentioned above measure wave motion though a combination of pressure and velocity measurements (the “PUV method”), which implies that they capture only long waves when the depth is greater than 10 m.

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