Sand catching structure for open beaches
Updated version
Gapped up structure:
Sand catcher artificial surf reef structure, v2 gapped up https://imgur.com/gallery/Y8HEYNt
whats the overall dimensions?
It can vary depending on the beach type but you can compare it to the length of rock walls with good waves next to it like Dbah for example. That groyne extends for about 300m from the high tide mark.
It cannot be built too deep like the Narrow Neck bags on the GC. It has to sit closer to shore so shallow breaking banks can form next to it.
Have to remember that 3 of the classics (Dbah, South Straddie, Ballina North Wall) have a large offshore river mouth sandbar that modifies the swell lines into peaks a long time before they get to the breaking zone.
Look at Dbah in a East or NE swell - fairly straight closeouts. But in a South or SE swell then it comes across the offshore bar and the classic peaks begin to form.
But then again, I've seen photos of pumping New Jersey where they have numerous rock groynes along a fairly small stretch of beach and they seem to get very good banks.
Offshore sandbars breakup and redirect swells that is true but this is about something else.
The idea here is to create banks closer to shore using an as cheap as possible structure causing as little environmental impact as possible.
In an open beach like Surfers Paradise we have times of good banks and bad (straight) banks. This structure will catch the sand travelling North and partially trap it creating a permanent good/shallow bank.
The structure has to be built big enough and shallow (close to shore) enough to become effective in creating nice big banks.
The key differences from a starndard rock groyne are:
1 - The sand catcher is not an ugly looking, unatural looking structure. It doesn't stick out of the surface.
2 - It allows to some of the sand to trave to the other side, over the top of it as well as through gaps.
3 - It can be shaped in more flexible patterns to create better banks, compared to straight rock walls.
4 - Less material/ time to build it.
Also remember, there are spots where rock formations on an open beach form good banks on both sides of it, without any bomboras altering the swell. I'd rather not name these spots.
After seeing how sand can build up around a tempoary structure, as in the Coffs sewerage pipe wharf ,which was dismantled after the pipes were laid on the sea floor,all i can say is that it went from no banks to unreal banks in a very short period of time and as soon as the wharf was demolished the banks went.Also the banks formed mainly on the northern side of the wharf in a few spots up to 50 meters away from the structure,so i suppose the pylons were enough to catch the sand in a type of sand slug .So maybe you dont need large objects to attract sand ,maybe only something sticking up out of the bottom by a meter or so as in short posts.Simple ,cheap and fairly easy.
I agree. The solution could be even simpler. The idea is using the right shape and size fprmation with the right depth to trap sand effectively.
@bukz.
Often thought about something like this myself. Even did a few 3d simulations years ago although it wasn't "physically" accurate. [Software is much better these days though so I'd love to see some proper simulations of what different shapes would work well]
I feel from your drawing that you may need to make the triangle shape less pointed as the Southerly shoreline sand drift tends to pack sand heavily on the southern side of any structure that is too perpendicular to the beach. [Also causes Erosion on the northern Side due to the sand being trapped] A more round-shaped tip in the ocean allows the sand to easily pass around the reef and not build up too much on the southern side.
I see why you wanted gaps in the middle to allow sand to pass but I feel that may make the sand banks less ruler-edged and stable and possibly prone to getting holes in the banks due to the turbulence
Keep up the good work and keep pushing people to think about this important issue, as the we need MORE waves to cope with the ever-increasing crowds.
Interesting info, thanks!
Hi bukz, its good to see ideas such as yours posted. Keep thinking. See my comment on these types of structures-https://www.swellnet.com/comment/783528#comment-783528
I uploaded the sketch to imgur.
I imagine this would be the cheapest way to create banks being based on the usual superior quality of waves right next to piers and rock groynes.
This would help to stop erosion by accumulating sand on 3 areas next to the structure with the added benefit of not being an eyesore.
On smaller swells waves would break right on top of the sand bags similar to those used at narrowneck. The idea is to bring it closer to the shoreline to be effective.
Link to image: http://imgur.com/gallery/x8TgnTQ