Still not really sure what your issues are or what is actually feasible - it looks like there are lots of other pipelines in parallel across what lokos like a beach or very flat piece of land.
At 65C, your weak point is the hot shrink sleeves. Pretty soon your CP system will be flat out protecting those joints, but where you get shielding of water, especially if it's slightly salty, your line will just disintegrate in front of you. SO I think you have a mojor bob to dig all the joint sup and do something a lot better with the field joints- probably fusing the field joint to the PP coating is what you need.
Other than that why do you feel the need to easily access this line. If it's well built and cared for you don't need access and just bury it and if you need to weigh it down with some concrete saddles. screw anchors are good, but in wet sand might struggle.
If you bring it above surface our issue is bending / buckling or upheaval.
Only other option is build a causeway from stone and place the pipeline in that, above the highest water level. Seems rather drastic to me.
Or re-route it?
We have about 5% of the information someone will need to do a proper costed assessment of the options.
someone needs to recognise that sand is not a great material when it gets exposed and wet....
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