Important
For this EarthCache you will probably need a stopwatch a calculator and some basic level maths. A metre ruler and tape measure and a large protractor could be useful.
This EarthCache would be most easily done at low or half tide. The best answers would be obtained by measing the beach slope at low tide and returning at high tide for heights and periods. Why? Well, the beach slope may not be the same as where the waves are breaking.
You could complete this EarthCache anywhere along the beach. The GZ has been chosen as it is relatively free from erosion.
Do not attempt this EarthCache if you can't meet the above.
Be mindful of the surf especially with young children
Background and what to do
Surf wave breaking is a phenomenon linked to the physical characteristics of a wave (speed, height, period) and their interaction with coastal morphology. Wave "Iribarren" numbers were developed via a series of lab experiments in order to classify different breaker types according to the wave height, wave period and beach slope. Coastal engineers consider these numbers in their planning particularly in situations where waves may run-up, overtop or reflect off structures or topographical features.
In order to calculate the Iribarren number you will need to find:
- Wave height in metres - try comparing wave to person of known height.
- Wave period in seconds - measure with a stopwatch the time it takes ten waves to arrive and average the number.
- Beach slope - Either calculate rise divided by run (in metres) or calculate the tangent of the angle of the slope.
Plug those numbers into the following formula and calculate to get the Iribarren number
The breaker type divisions according to different values of the iribarren number are as follows:
Less than 0.4: spilling
Between 0.4and 2.0: plunging
More than 2.0: surging
What this obviously confirms is that steep waves on flat beaches tend towards the spilling end of the spectrum and longer waves on steep beaches tend towards the surging end.
Further reading: Komar, P., 1998, Beach Processes and Sedimentation, (2nd ed) Pren. Hall.
Logging Requirements
0. Preface any email with GC3T8AR Breaker Breaker in the subject line and title and clearly note the question number and answer. Do not wait for a confirmation email to log but be prepared to be asked for additional information if your answers are slim.
1. Report the Iribarren number, the wave type this translates to and the general location where you were.
2. An uploaded photo of the wave conditions would be nice but not necessary.
Email answers to gcstegan"at"gmail.com
2012 Stegan's EarthCache Masters Programme
It is not very feasible for many New Zealanders to get past the Bronze level on the earthcache.org programme becase you need three states for Silver which means leaving the country! So, as in 2010 I've decided to run a little sideshow on my new earthcaches this year... with the following points system:
5 points: First to find
3 points: 2nd to find
1 point: Logging a find
1-5 points: Special bonus questions.
At the end of 2012, I'll issue certificates for 1st, 2nd and 3rd.
Updated information and Leaderboard at: Stegan's Earthcache Programme
