De Nederlandse website over muien. The Dutch website about RIPS.

Feeder current

The feeder current is an important detail of the fixed rip. It is often difficult to spot the neck of the rip, but the feeder current can be spotted in most of the times.  If you can spot a feeder current you know he is flowing to the neck so you can guess where the rip is located. In the area between the neck, the edge of the sand bar and the trough some interesting things are going on. See figure 1.map002

The first thing is that the waves entering the trough will have more friction at the side of the neck compared to the deeper part in the neck. The effect of this will be that the wave direction will change into the trough. The direction can differ 90 degrees from their original direction. This effect can also be visible on the sand-bar. You see waves moving parallel to the beach in cross direction with the original wave direction causing funny effects. Sometimes the wave direction is over 90 degrees, causing the wave going back to the sandbar. However when he meets a wave coming from the sea they will hit each other, causing splashing water. This effect is also known as shear-waves.

A second effect is the wave shape. Waves moving in the same direction as the current have a smooth shape (fig 2A). Waves moving against the current become hooky (fig 2B), sometimes they break and the wave lengths will become smaller.

map003

These 2 effects, wave direction bending and wave shape change are the 2 aspects to recognize a feeder current. After you spotted te feeder current you can tell where the rip must be located.

The next slide show is an attempt to clarify this.

  • Wave direction B to the left, current to the right, rip at C.

We discussed the feeder current now and go on with the neck of the rip.