Explanation Of Picture Of Sand Banks And Troughs - 30 June 2011

 2015-09-02 04:05 PM by

Picture 1– in this picture there is a very obvious trough very close to the beach where there is no evidence of white water and there is a little wave that has just come off the sand bank at the back. The left hand side of the picture shows that the trough is wider and in all probability gets wider and wider out of picture.

You will also find that this kind of formation tends to turn and flow out to sea which is what we would call a "hole" especially once the tide comes in. This picture is obviously a low tide picture. This trough on the inside of the bank will not have much water movement on the right hand side of the picture where it is at its narrowest, but as the waves roll in over the sand bank at the back, indicated by the white rolling water, they fill up this inside trough and the current would be going from the right hand side to the left hand side of this picture. As the volume increases going progressively left and out of picture, so that trough would get deeper forming a hole or rip going seaward. If you look at the top right hand side of the picture you will notice in between the last wave right at the back of the bank and approximately half way down the picture, an area where the wave is not rolling white but is almost trying to form, my guess is that if you go to the right hand side of the picture out of picture, you will find the same hole going seaward as I have just been describing on the extreme left hand side. On this particular beach the inshore current is obviously right to left and hence this almost continual succession of sandy points and bays down the beach with these little bays or troughs all going seaward. These become the holes on the high tide.



Picture 2– shows two very distinct channels running parallel to the shore, with two distinct sand banks indicated by the white water. If one looks right at the back of the picture you will see the white water caused by waves breaking on a back bank and then you will see the distinct clearer water of a channel that one could certainly throw into, especially if you waded through the inside channel or trough and onto the first sand bank in the picture. If one were able to see a much bigger picture there would be a channel or hole on both the left and right hand side of the first sand bank which will only really show itself given the right wave action, but whenever water comes in over a sand bank into a deeper inside channel it has to go out somewhere. As I mentioned in the articles, a dead flat sea is going to reveal very little and an extremely rough one will just smother any chance of being able to read what lies underneath by watching how and when the waves break.



Picture 3- All three of these pictures were obviously taken on a low tide, but this one is very interesting because there is a definite little hole very close to the beach on the middle and left hand side of the picture, whereas on the right one can see the sand almost forming a little sandy point. This inside hole will definitely fill up on the high tide and be a good spot to fish. The interesting part is at the back where there is again evidence of two deeper channels with sand banks in between. You will notice right at the back of the picture on the right hand side there is a wave curling and foaming in the middle. Behind that there is white water (sand bank). Where it is curling and breaking, the wave has obviously passed through a deeper channel and formed a swell, which is now curling to break on a shallower bank. On the very left hand side about ¾ of the way up is another swell curling to break which too has obviously passed through a deeper section or channel, thus forming a swell (white water behind it) and now curling to break on the bank. On the same swell on the right hand side you will see white foam on the swell - obviously the remains of a bigger wave that has passed through and actually broke on the right hand side, indicating that the right hand side is shallower than the left hand side where there is no foam left on the water from the previous wave. These pictures are very interesting and it would have been fantastic to have had exactly the same picture taken on the high tide, a half way out tide, a low tide and a half way in tide. All four would have looked quite different, but bearing the state of the tide in mind, all four pictures should have revealed pretty much the same sort of information as these ones have. One must also take into
account that just one picture is nowhere near as reliable as when one sits and watches the wave action for five minutes or so.



Below is all 3 pictures together