Waves
From Trail-Finder -- Dedicated to getting you outside
Contents |
Overview
Waves are moving, water-based hills. As hills, they need to be climbed, circumnavigated, and overcome. Moving just makes it all the more difficult.
Impact on Activities
For hikers, waves might be an issue if you're on a seaside trail and the waves are breaking over the trail. This is very rare. Normally, the only activity which is impacted by waves is open-water watersports, such as canoeing and, more commonly, sea kayaking. Of the two, sea kayaks are especially well built to handle waves. With an enclosed deck, waves stay out of the boat, and with a long, straight, narrow hull, they easily ride over waves of a couple meters high, or even more.
Scuba divers are also impacted by waves, but mostly while on dive boats, or while entering or exiting the water. Once divers are twice the wave height underwater, there is no longer an impact from the waves.
Nomenclature
- Break: Waves generally break when the water shallows to less than twice the wave height.
- Calm: Little or no wind. This will not generate waves.
- Downwind: If the wind blows past you, then to a lake, the lake is downwind of you.
- Fetch: Waves get bigger the longer distance the wind has to blow across the water. Fetch is the distance the wind has blown over the body of water to get to your location. Since the fetch is much shorter on the lee side of an island, the waves are usually much smaller.
- Lee: The lee side is the downwind side of something. This is normally used at sea to indicate the sheltered, downwind side of an island or other land. Same as leeward.
- Leeward: The leeward side is the downwind side of something. This is normally used at sea to indicate the sheltered, downwind side of an island or other land. Same as lee.
- Light and variable: Very little wind, but with mild gusts. Light and variable winds can help to cool you on a hot, summer day, but won't generally present any problems or risk of hypothermia.
- Peak: The top of the wave.
- Trough: The bottom of the wave.
- Upwind: If the wind blows past you, then to a lake, you are upwind of the lake.
- Wave height: The maximum height of waves, from peak to trough.
- Wavelength: The distance between waves.
- Windward: The windward side is the upwind side of something. This is normally used at sea to indicate the exposed, upwind side of an island or other land.
Mechanics
Waves are formed by wind blowing over open water. The height of the wave is determined mostly by two factors: the wind speed and the fetch. Fetch, the distance the wind can travel unobstructed over water, contributes to higher waves, but a large fetch will also make smooth, regular waves.
Waves have a distinct height, the distance between the vertical peak and the trough. Waves also extend underwater a distance roughly equal to the height. If the water depth is at least twice the wave height, the waves can travel unobstructed. As the bottom shallows, however, the waves start to grow, and eventually break. The area where waves are breaking is generally the most dangerous, if the waves are large. Breaking waves can also indicate underwater obstacles, such as large rocks or reefs, which you should generally avoid.
Current, easiest to see in rivers, also exists in many large bodies of water, including the Great Lakes and all oceans. Currents can increase, or even cause, waves.
Tides, the movement of large bodies of water, mostly oceans, caused by the gravitational pull of the moon, can also contribute to increased or decreased waves.
Predicting Waves
Like wind, in many areas, waves can be predicted, and generally follow relatively predictable patterns. Normally, wind speeds and, consequently, wave heights, peak mid to late afternoon. Wind speed is normally calmest in early morning. This can be used to your advantage, planning large, open-water crossings first thing in the morning, with the more sheltered parts of your travel, or even short hikes in the middle of your kayaking trips, planned for mid-day.
Cold fronts will also usually bring in strong winds and high waves. If the temperature starts to drop quickly, or the barometer starts to drop, you can expect the wind and waves will pick up.
Where possible, checking a weather forecast, and even having some weather forecasting skills of your own, can also help a great deal in predicting wave intensity.
