Sometimes the work cannot be reached from the bank and a barge is not practical. The platform then becomes the first construction operation on the job, and it is worth designing rather than improvising.
When it is worth building
No standing position on land with a line to the work, and the reach required exceeds what any available machine gives from where it can stand.
No barge access, because the water is too shallow, too narrow, or unnavigable.
A long run where repeated repositioning from land would be slower than building a platform once.
Soft ground that will not carry plant, where the platform is a bearing surface as much as an access route.
Repeated access needed over a period, rather than one visit.
Against that: a platform is a construction operation with its own cost, its own permitting, and its own removal. On a short scope it frequently costs more than the work it enables.
What it has to do
Carry the plant. The loaded machine, at its working configuration, plus anything else on it.
Stay put. A temporary structure in flowing water is subject to the same forces as the permanent works, and it usually has less design behind it. On a river with a risk of an event during the works, that is a real exposure.
Not obstruct flow unacceptably. A causeway across a channel is a contraction, and it raises water levels upstream while it is there. On a mapped floodway that has a regulatory dimension as well as a hydraulic one. See floodplain permitting and no-rise.
Come out afterwards, completely.
Why bagged units suit the application
The bank covers how units used for a temporary work platform can be removed after construction, and the answer is the property that makes this work.
They are recoverable. Units are lifted out by the same plant that placed them. There is no demolition, no material to break up, and no residue.
They are placeable in water without dewatering, which is the whole point of needing a platform in the first place.
They conform to an irregular bed rather than needing it graded first.
They are reusable, subject to condition. Units recovered from a platform may go into the permanent works or into the next job. See end of service life and recovery.
Compare with imported rock fill for a causeway, which is placed loose, mixes with the bed material, and cannot be fully recovered. That difference is frequently what makes a temporary platform permittable at all.
The removal plan is part of the design
This is the point most worth taking from the page.
A temporary structure in a water body is authorised on the basis that it is temporary. The authorisation generally depends on it being removed and the site reinstated, and a regulator assessing the application will want to know how.
So the removal method belongs in the design and in the submittal, not as an afterthought:
- How the units are recovered, and with what plant
- When, relative to the permanent works
- What condition the bed is left in
- What reinstatement is required
- What happens if some units cannot be recovered
That last question deserves a real answer. Units that have settled into a soft bed, been buried by sediment, or become inaccessible are a foreseeable outcome, and a plan that assumes complete recovery without addressing the alternative is incomplete.
Permitting
A temporary platform is placement of material in a water, which means it is regulated in its own right:
- Section 404 applies to the fill, temporary or not. See Section 404
- Section 10 where the water is navigable, on obstruction grounds. See Section 10
- Floodplain and no-rise, where it encroaches on a floodway
- The in-water work window covers the platform’s installation and removal as well as the permanent works, which means both operations have to fit inside it. See in-water work windows
That last point catches programmes out. Install platform, do the work, remove platform — all inside one window. On a short window that sequence may not fit, which is the same arithmetic that rules out dewatering on some sites. See what dewatering really adds.
The alternative worth pricing first
Before committing to a platform, price the barge.
A marine spread has a large mobilisation and a day rate, and it needs navigable water. A platform has a construction cost, a removal cost, its own permitting, and it consumes window time at both ends.
Which is cheaper depends on the scope, and it is worth doing the comparison rather than defaulting to whichever is more familiar. See barge and vessel-based placement.
Where to go next
- Site access and staging
- Barge and vessel-based placement
- In-water work windows
- End of service life and recovery
- The rock bag FAQ for the inland infrastructure section
- The installation hub for the rest