Intro to Rock Gardening: Understanding Waves

Part three of our rock gardening skills series

By Bill Vonnegut

Rock gardening is heavily dependent on ocean conditions. As we’ve discussed in previous posts, the coastal features that make great play spots can change dramatically with tide and shifting conditions. While some assessments of the risk-fun ratio have to be made on the water, others can be made much earlier. Before leaving the house to go paddling, I always check the marine forecast to see what the ocean is doing. I assess what the conditions are (wind, weather, swell height and period) where I am planning to go, and decide if it will be the kind of day I'm looking for.

Lily Kelsey, Tony Johnson and Allen Shah enjoying some waves at Point Lobos Ca. - Photo by Bill Vonnegut
Lily Kelsey, Tony Johnson and Allen Shah enjoying some waves at Point Lobos, California. Photo by Bill Vonnegut

If you’re new to reading ocean forecasts, take some time to understand what the different terms mean and how they interact. Next time your at the ocean, stand on a cliff observe the water. There will be a steady pattern of rounded humps as far as the eye can see. These shapes are the ocean swell. One of the things the forecasts report on is the swell period, which the distance in time from peak to peak of an ocean swell. To understand swell period, pick a fixed point out on the ocean such as a buoy and count how long it takes for each peak to pass by the buoy; the number of seconds is the swell period. The forecast will also tell you the swell height, which is measured from the base to the peak of the wave.

Together, the swell period and height determine the wave size and how far off shore they will break. Consider this: a wave not only breaks at a depth 1.3 times its height, but also begins grabbing the sea floor at half its width (peak to peak). For example, all two-foot swells in the open ocean are two feet tall, but as they approach shore, a two-foot swell with a twenty-second period carries a much greater volume of water than the same sized swell with a ten-second period. The two-foot, long period swell will build up into a much taller wave and break farther from shore. A longer period swell grabs the bottom in deeper water, which slows it down and causes it to build height, making it break in areas that are otherwise safe on short period days. In short, waves with a longer swell period and greater height will break farther from shore with more power. And the size of the waves will greatly affect a day out rock gardening.

Finally, ocean forecasts tell you the swell direction. If you have a favorite play spot that you return to often, you’ll quickly learn which swell directions are best for that area.

Start by going out on smaller days and work your way up. Get to know how different conditions affect different rock gardens. Beginners may want to check out surfing videos to learn more about understanding waves. Stay safe and see you on the water.

––Bill Vonnegut is a sea kayak instructor at California Canoe & Kayak and member of the Neptune's Rangers paddling posse. Check back for an eight-part rock gardening series where Bill will discuss the techniques, skills and gear needed to enjoy coastal whitewater.

–Want to take the next step with your rock gardening? Kayak symposiums bring in the top coaches from around the world, making them a great place to take your paddling skills to the next level. There are a couple great sea kayak symposiums coming soon to the West Coast. The first is Lumpy Waters coming to the Oregon coast on Oct 16-18. Then on Feb. 5,6 & 7 head to California for Paddle Golden Gate in the beautiful San Francisco Bay Area.

–Check out MORE ROCK GARDENING SKILLS from Bill Vonnegut.