Current Interaction With Waves
Currents are the movement of water from one place to another. They can be large-scale and consistent, like the Gulf Stream, which flows from the Gulf of Mexico up the eastern coast of the USA, continues to Newfoundland, and then crosses the Atlantic Ocean as the North Atlantic Current. Similarly, the East Australian Current (EAC), which Nemo (in the movie Finding Nemo) famously “rode,” flows from the Coral Sea down the east coast of Australia. These ocean currents consistently flow in the same direction, often traveling thousands of miles.
In addition to these global currents, there are local currents driven by tides. These tidal currents change direction and velocity with the tide. During high tide or low tide, the current slows significantly, creating a period known as “slack water,” when water velocity drops to near zero.
A Rough Ride
Boating becomes challenging as sea state conditions worsen, particularly when certain factors exacerbate waves and swell:
Current and Waves Interaction: When currents meet waves from different directions, they can create a confused and heightened state of waves. This often results in choppy conditions with shorter wavelengths, making navigation difficult.
Swells and Waves Superposition: When swells meet wind-generated waves, their superposition can significantly increase wave height and create chaotic sea conditions.
Distance from Shore: An offshore breeze can cause waves to grow larger in height as they move farther from the shore.
Water Depth: As water becomes shallower, wave height increases while the waves also become steeper, leading to a rougher ride.
Understanding these factors is crucial for safe and comfortable boating, as they can dramatically affect sea conditions and vessel handling.
At the very North of New Zealand at Cape Reinga, two ocean currents meet — one from the Tasman Sea and the other from the Pacific Ocean. The waves seen here are the currents meeting in deep water – yet they are dangerously breaking. What if you were motoring using just your GPS at night – without thought to two currents meeting?
