Introduction

Waves are the beating heart of the coastline, and surfers rely on particular wave conditions in order to practise their sport. Waves are affected by three main factors: 1. Wind speed and direction; 2. The gradient of the beach that rests offshore; and 3. The height of the tide (and how much of the offshore beach is exposed).

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Length of time

Half day, covering both a high and a low tide time.

Suitable location

A medium- to high-energy coastline.

Equipment needed

Stopwatch; Device to take video footage; Digital anemometer; Thread; Compass.

Key skills

• Finding the mean and median of different values.
• Appreciation of the inaccuracy of wave height measurements.
• Drawing a radial graph to show the different strengths and directions of wind at the chosen coastline.
• Drawing a mind map showing how wave period, wave height, wave swash time, wind speed and wind direction are interconnected.
• Analysing and comparing the features of the waves at high and low tides.

Suggested delivery

Students will be measuring five features of waves:

• The wave period (the time between successive wave breaks).
• The wave height (the distance between the wave crest and the wave trough).
• The wave swash time (the time between the start and finish of a single swash).
• The velocity of the wind.
• The dominant (prevailing) direction of the wind.

Prior to conducting the primary data collection, students might wish to think about how these features may support surfing, and what would be the ideal surfing conditions under each of these factors. #

Wave period: Students can measure the wave period by measuring the time it takes for successive waves to pass a fixed point, such as a support for a pier. It is recommended that students measure for at least twenty waves; an average time is then calculated.

Wave height: In general it is not advisable for students to attempt to measure wave height in the water. Instead, they should estimate the difference between the trough and crest of the wave as it passes a fixed point such as the support of a pier. Students may benefit from taking a short video of the waves as they pass so that this can be replayed and more accurate measurements recorded.

Wave swash time: Students can measure the time between the point at which the swash breaks to the point at which it has disappeared.

For wave period, height and swash time, it is recommended that students measure at least twenty waves and then calculate an average from these measurements.

Wind velocity: Using a digital anemometer, students should face into the wind and hold the anemometer such that the fan can move freely in the wind. Students can monitor the maximum and minimum velocity readings in a two minute time period and then record the median value between these two measures.

Wind direction: Students can hold a piece of thread at one end above their heads and record the main direction in which the thread moves by the wind using a compass. Remind students that the wind direction is recorded as where the wind originates from, not where it is blowing towards.

These measurements can be carried out on the beach at low tide and from a safe vantage point at high tide. Students can then decide whether the conditions that day represent fair, excellent or poor surfing conditions.

Students can have a discussion about which of the factors they have measured has the most impact on the surfing conditions and which of the factors they have measured in the field they would change on that day in order to improve surfing conditions.

Potential risks to consider

• The position of the tides at the time of the activity, how high they are, and are likely to get, and when the peak tide will be.
• Students entering the water, either intentionally or by mistake (especially in coastal areas with known riptides).

Possible follow up activities

• Students can use mapping software to measure the length of the fetch for the coastline they have studied, as well as others around the UK, and use these to find surfing hotspots.
• Students can use historical wave data from surfing websites to compare winter and summer wave conditions.

Resources

Magic Seaweed

Windfinder

This collection of Fieldwork activities were created by Paula Richardson and the Fieldwork and Outdoor Learning Special Interest Group (FOLSIG) for the National Festival of Fieldwork, the GA invites everyone to take part during the summer term.