Sand catching structure for open beaches
whats the overall dimensions?
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.
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.
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.
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