5. Determine the contract depth by adding the advanced maintenance dredging requirement to the design depth
requirement. The advanced maintenance dredging is the additional depth to reduce life-cycle maintenance costs by
decreasing the frequency of dredging. Base the quantity on the anticipated local channel sedimentation rates
corresponding to the anticipated dredging cycle. Unless an economic analysis is performed, use a dredging
frequency of not less than 3 years, but based on local conditions. Include a minimum of 1 foot advanced
maintenance dredging to prevent contractor change orders for differing site conditions on future maintenance
dredging contracts. This minimum also provides the Contracting Officer field flexibility if the contractor does not
achieve the contract depth in spot locations. The dredging tolerance, or overdredge, is the additional depth below
the contract depth paid for by the dredging contract. The contract permits this additional depth because of
inaccuracies in the dredging process. It is normally either +1 or +2 feet. Local conditions and anticipated
dredging equipment may warrant a different value. NAVFAC Textbook DM 38.2, "Dredging Equipment"
provides additional information.
6. Determine the permitted depth by adding the dredging tolerance, or overdredge, to the contract depth.
Material samples for environmental testing should be accomplished at least to this depth.