From Dredged Volume to Payable Quantity

Production and recognised revenue

The dredger incurs costs through time, fuel and equipment use. A contract may pay for the measured change in the seabed. Siltation, survey timing and the agreed calculation boundary sit between the two.

At New Mangalore, the final account for a maintenance campaign reduced a previously recorded quantity after siltation. The contract's measurement and risk allocation determined the revenue available for work already undertaken.

A risk written into the tender

India's auditor recorded a joint pre- and post-dredging, in-situ measurement basis, with dredging-period siltation allocated to the contractor. Zone-IV's recorded quantity fell from approximately 2.045 million to 1.859 million cubic metres in the final running-account bill. The audit criticised the omission of siltation from the estimate. Management cited pandemic, plant, hard-strata and cyclone effects; the audit addressed those explanations.^[1]

The issue was the conversion of production into contractually recognised quantity. It should have been part of the revenue model before the rate was submitted.

Keep three quantities visible

Hopper and transport records describe loading and movement. In-situ measurement describes the change between agreed seabed surveys. Payable quantity follows the contract's rules for eligible volume and adjustment.

These records can be reconciled, but their values need not coincide. Water content, bulking, settlement, re-siltation and measurement uncertainty affect comparisons. A production report should identify its basis rather than label every number simply as cubic metres.

The bid model needs a traceable route from plant output to recognised revenue. It should show the expected operating cycle, the conversion to the relevant measurement basis and the contractual treatment of rework or re-siltation. Validate that conversion as rigorously as the vessel production estimate.

Survey timing is a commercial interface

The measurement plan should specify when a completed area will be surveyed, who will attend and how quickly the data will be processed. If the whole site is measured only at final completion, early work may face a much longer period of re-siltation exposure.

Sectional measurement or acceptance can help where the project and contract support it. The arrangement needs defined boundaries, acceptance criteria and responsibility for later maintenance. Issuing a sectional certificate without resolving the continuing obligation leaves the underlying risk unclear.

The owner also needs dependable operational depths. Measurement arrangements should therefore be developed with the delivery sequence and harbour requirements, rather than added as a payment concession after the campaign has started.

Make the quantity reproducible

The final number should lead back to the original survey files and agreed processing rules. Coordinate and vertical datums, tidal corrections, grid resolution, dredging limits, tolerances, allowable overdepth and excluded observations should be identifiable.

Revisions need a reason and a version. A changed boundary or processing rule can alter the account even when both parties hold the same sounding data. Commercial staff should be able to locate the technical explanation without reconstructing months of correspondence.

A quantity disagreement should identify the affected area and amount. Agreed work elsewhere can then continue through certification under the applicable payment provisions.

Record the cause of waiting

A log stating six hours of stoppage leaves several questions unanswered: which vessel was affected, was it available to work, what prevented the operation and who controlled that condition?

Traffic restrictions, unavailable workfronts, weather, machinery breakdown and fuel shortages need separate records. Start and finish times, position, equipment status, notices and the instruction source support operational decisions and valuation.

Normal harbour interference and compensable interruption may have different contractual treatment. The tender should make the intended allocation clear; the contractor should price the exposure it accepts.

Put measurement into bid review

IMWO calls for tender documents to include available survey data, dates, known limitations and the measurement rules. Unresolved material conditions should be addressed through investigation, clarification or a defined adjustment mechanism.

Bid review should then compare the production basis with the payment basis. During construction, the register should distinguish quantities submitted, agreed, under review and rejected, with reasons and references. This gives the team a practical way to examine the gap between what the vessel reports and what the contract recognises.

Source

^[1] CAG, Report No. 18 of 2025, printed pages 157–159, sectionA.4 and management/ministry responses; PDF pages 195–197. Body quantities are rounded; the exact final-account difference appears separately in the footnote. Original report.