Placing armor without dewatering is the property that puts bagged units on jobs where the alternatives are awkward. The trade is that you are working blind, and the discipline that goes with that is the whole subject.
The methods, by depth
Excavator from the bank or a platform. Shallow water within reach. The most common arrangement on rivers and small channels.
Crane from land or barge. Deeper or further out. See barge and vessel-based placement.
Diver-assisted. A diver guides the unit to position and confirms placement. Adds accuracy and confirmation at the cost of a dive operation with its own planning and safety regime.
ROV. Depth beyond diving, typically offshore. The ROV provides the eyes and often the positioning reference.
The bank covers placement approaches across these, and the marine and offshore section covers subsea specifics including tolerances above a cable or pipeline.
Working blind
Because you cannot see the bed, placement is measured rather than judged:
Work from a survey reference. A known point, with position taken from it, rather than from what looks right over the side.
Count and record as you go. Which unit went where, in sequence. This becomes the as-built.
Probe to confirm. Where depth allows, a rod tells you what the previous unit did and whether the bed is where the survey said.
Build from a known edge inward. Each unit has a reference in the one before it, rather than every unit being placed independently into the dark.
Accept a coarser layout. Placement accuracy underwater is lower than in the dry, and the layout should assume that rather than requiring precision it will not get.
The bank covers how accurate placement is documented when water visibility is poor.
Controlled lowering
The bank addresses controls that prevent impact damage while lowering, and whether there is a maximum allowable drop distance. The specific limit is a manual question and this site does not state one — see lifting and rigging.
The principle: a controlled lower places the unit; a release drops it. Underwater, a released unit also lands less predictably, so control buys accuracy as well as protecting the mesh.
Sequence
The bank asks whether placement should begin at the downstream end, the upstream end, or the lowest elevation, and the answer shapes the whole operation.
The general principles:
Start at the toe, or the lowest elevation. It is the most critical zone, the hardest to reach if conditions worsen, and the part that arrests the mechanism. See toe protection.
Establish edges early. Flow works at unprotected boundaries, so a partially complete installation with defined edges is more stable than one with a ragged perimeter.
Leave the site defensible at each stop. Work halts for weather, tide, and shift ends. What is in place should be stable on its own.
Separation from existing assets
On subsea and utility work this is the governing constraint rather than a detail.
The bank covers how placement tolerances are established above a subsea cable or pipeline, and how safe separation is confirmed during placement. It also covers whether a unit can be retrieved or repositioned if it lands outside tolerance — which it can, and that recoverability is a real advantage over systems that cannot be adjusted. See rock bags vs grout bags subsea.
Where clearances are tight, discrete placement with a defined tolerance is the argument for this method over dumped material. See rock bags vs fall-pipe rock dumping.
Proving what you placed
Separate from placing it, and frequently under-scoped.
As-laid survey is what turns an installation into something assessable. Without it, nobody inspecting in five years can say whether units have settled, moved, or gone, because there is no datum.
The bank covers what offshore survey records belong in the final as-laid documentation. Agree that scope before the vessel sails or the crew mobilises, not afterwards.
Methods depend on the setting: sounding survey, multibeam, diver survey, ROV video with positioning, or a combination. The requirement is a record of what is where, at what elevation.
The turbidity question
Placement disturbs the bed and releases sediment, and that is regulated. Turbidity limits usually arrive through the state water quality certification rather than the main permit. See construction stormwater permitting and Section 404.
Working without dewatering is a large reduction in overall disturbance and worth stating as a minimisation argument in a submittal — see what an agency reviewer wants to see. It is not zero disturbance, and the controls still apply.