Ocean outfall installation techniques

[Trevr]

I need to install a outfall pipeline at a dissipatave beach (1:80, fine-medium sand, low energy enviro). The pipeline will be approx. 250>350mm HDPE or similar. The pumped material will be clean seawater, discharge from beachface dewatering (beach drainage) system. Max. water depth probably only 1m at low tide (tidal range 1.4>1.8m). total length say 250m from front of dune system. Distance to low water 100m average.

I would be interested to hear about any inovative low cost installation techniques - particularly seaward of the low tide mark.

Regards, Trevor
beachdrainage.com

 

[desm]

If the pipe is to be installed in a trench and then backfilled, I suggest a small backhoe dredger for digging the offshore trench (seaward of low water mark), and land based excavators for the inter-tidal zone. The pipe string can be fabricated above the high water line (if there is enough room) and dragged down the beach and installed in the trench at low water using the same plant mentioned above. Concrete weight collars on the pipe or stone mattresses over the pipe can be installed to provide temporary stability for the pipe until the trench is backfilled. Very general description, but I think it's the cheapest method. Looking for a company to install the pipe? We have installed many outfall pipelines in UK and overseas.

 

[StephenA]

I agree with the answer from desm except that I would use land based plant for the excavation in 1.0m of water. It depends on the wave action, but a pedestal mounted excavator will easily work in 1.0m of water and it would avoid the cost of mobilising a backhoe dredger. We have also installed many outfalls in the UK and around the world, and would be interested.