LEARNING INTENTION

To understand the effects of wind on the sea

DISCUSSION

Have you wondered where waves come from? 

What is making the water move? 

Waves are energy from the wind making the water go up, down and around. The faster, the further and the longer the wind blows the bigger the waves will grow.

Why are there still waves at the beach, even when it is not windy? 

If the wind stops, or changes direction, the waves will stop growing, but they won’t stop travelling. Waves keep travelling away from where they were created, sometimes for days, until they run into something like a beach. So, when you look at the waves breaking at the beach, those waves might be at the end of a long journey.  They may have been created thousands of kilometres away, or they could have been created near you.

Wind and waves and how they are made, thanks to Mathew from Mangawhai Beach School for the winning video! 

Oceanographers have measured waves in the Southern Ocean and have watched them travel across the Pacific Ocean all the way to the beaches of North America, more than a week later.

Storms can make enormous waves. If waves from two different storms collide they can create “freak waves”.  Some have measured around 25 metres high.  That would be like five giraffes standing on top of each other!

What are swells? 

Swells are rolling waves that travel long distances through the ocean. They are not generated by the local wind, but by distant storms. Swells are typically smooth waves, not choppy like wind waves. A swell is measured from the crest (top) to the trough (bottom).  

To measure waves like a scientist you need to understand the characteristics of a wave:

The amplitude measures the waves height from the sea level, to the crest (top) of the wave.

The wave height is measured from the trough (bottom) of the wave, to the crest.

The wavelength measures the distance from crest to crest.

The wave period is the time of one cycle from one crest to the next.

Activity: 

Marine reports, measure and label a wave.

Draw a wave and label the crest and trough. Measure the amplitude, height and wavelength.

Look at the Met Service Marine report for today in your area:  https://www.metservice.com/marine

• What does it tell you about the sea state, wind and waves?

There are several weather buoys around the coastline of New Zealand. These collect and record data about the weather, water quality and even the size of the waves. See if you can find a weather or wave buoy near to where you live.

There is a wave measuring buoy just outside Wellington's Taputeranga marine reserve. It provides wave information for shipping and forecasting. Have a look at the data here. 

The Canterbury wave buoy is moored 17 kilometers east of Le Bon’s Bay, Banks Peninsula. It sends information about the waves every half hour. Check it out here.

The Port of Tauranga has a weather conditions monitoring system. This is updated every three minutes giving you wave height, wind direction and other weather information. Check it out here.

Bowentown wave buoy, on the Bay of Plenty coastline shows not only wave height, but also water temperature. View the data here.

Over a two week period choose one of the sites (or find your local site) each day providing data on:

1. Wave height
2. Wind direction
3. Wind speed

• What conclusions can you draw about the relationship of wind to waves?

One of the things many people love about the ocean is the waves. People love to play in the waves, surf the waves, and the sound of the waves crashing on the beach. 

• What are some of the dangers to watch for when we are in the waves?

GLOSSARY