Artificial reefs to create surf

[Prepakt1]

I am working on various designs and construction methods
for an artifical reef in the Uk to create surf for recreation and also provide some shore protection. The reef requires specific slope profiles.
We have various options from a sand filled bag core covered
with concrete fabric mattress to an all concrete reef of Prepakt concrete (basically rock filled with pressurised
concrete to fill the spaces} Probably too expensive.
Sand filled bags alone have been used in various locations with partial success they move and get damaged.
I would like comments from anyone who has tried this type work and anyone who has used stonger material than nylon
in marine applications as we might make large samd filled bags out of a really strong fabric .
Dave Ritchie
Intrusion Prepakt Canada

 

[swBausch]

I would question the economic return on such a project, but here in the States certain legislators ensure the loyalty of voters by restoring the sandy beaches of vacation hotspots. This is not cheap, nor long-lived.

What sort of "surf" do you want?

If you want Surfer's Paradise waves, that's all about a gradual ramping to the beach. A skewing of the ramp provides the left-to right 'breaking' of the wave. I am sure that depth-finders and GPS would allow the proper placement of materials, but what sort of materials?


My wild and crazy guesses involve a dense grid of helical piles that protrude as a "bed of nails" resembling the desired profile. Similiar to the pegs that concrete finishers use to accurately place concrete. Only in this situation they are permanent, not pulled out, and they are intended to stabilize the profile.

Then what....? Concrete can be placed underwater, though the mix might be expensive and placement problematic.

Or..... a seawater-resistant version of Gabion baskets could be attached to the piles. The baskets could have vertical tubes placed in them. Place the baskets, and attach to the seabed with helical piles ran down through the tubes. Baskets of various sizes would be needed. I assume basket orientation/aspect ratio would be critical.

Whatever you do, I don't think you can avoid "drilling" them to the seabed.

 

[dicksewerrat]

Ever thought of concrete filled waste auto/truck tires. tied together as mats. They could be laid in almost any profile. and you can get them fairly cheaply.

 

[Prepakt1]

We could use tyres and have dismissed them as they tend to fail at the joints. You can use them by making the reef profile onshore and floating them to location and sinking them by filling tyre columns with a fabric bag and at location pumping in concrete or sand.Vehicles filled with concrete we have used before, but as the area is sensitive,
tyres and cars are not likely be appreciated in this environment.The is also a need for cushioning /weed growth to be encouraged. Helical piles or plate anchors may be used to anchor the concrete mat to the seabed, or we might
just make it extremely thick 18' for example and the weight will hold it down.
The reef design is a large open U shape.

There are several reefs under proposal for the UK and the economic return is O.K.Few smaller ones have been already installed in other countries mostlty sand filled bags.

 

[jdmm]

Following your sand bag approach, could you use a proportion of cement in each bag that would set in place. This would allow a thin bag that would deteriorate and the sand would set.

Since this approach has been used for decades for culvert headwalls, no royalty need be paid to me.

 

[Prepakt1]

You can use a sand cement mix .PrepaKt frequently uses sand /cement mixes and developed all the original soil cement processes and technology in the 1950 s. We have our own patents and royalties.This is the ocean and you will need something stronger for a covering .A 10% sand/cement ratio may be used in bags as a core .Solid Concrete will eventially degrade in the surf zone so weaker mixes have a much shorter lifetime but will stop sand washing out of any ruptures in the fabric bags.
Gabion baskets I agree,will probably work well as a core filled with rock or gravel.
Intrusion Prepakt

 

[clayR]

Dave,
I like your grouted rip-rap approach, and along those lines could it be possible to use highway barriers as forms for the rip-rap. Perhaps the barriers could be tied together with steel brackets spaced at the desired width? The space between the barrier could then backfilled with rip-rap and grouted. How to accomplish grouting is more difficult, but could be done with perforated injection pipes placed prior to placing rip-rap, say 6" pipe driven into the floor spaced 6-8'each way extending to the surface. The pipes will provide some resistance to uplift depending on the embedment length below the sea floor, as well tie together multiple lifts if you needed to go higher than 4'.