Maintenance Dredging

Maintenance dredging maintains navigational depths while minimizing environmental impacts from sediment disturbance and disposal. This may include, among others, environmental impact assessments and approvals, sediment quality testing and classification, use of low turbidity dredging techniques, designated spoil grounds or containment areas, beneficial reuse of dredged material (such as land reclamation or habitat restoration), and monitoring of water quality and turbidity during operations.

For DMC ports, maintenance dredging can help maintain safe navigation and port functionality, minimize damage to marine habitats, reduce contamination risks, support coastal protection and restoration projects, and support compliance with environmental regulations (CEDA and IADC, 2018; PIANC, 2023). As vessel sizes increase, the scale of dredging programs in some DMC ports may also increase.

Maintenance dredging is the periodic removal of sediment that accumulates in navigation channels, berth pockets, and turning basins, to maintain the water depths required for vessel access and manoeuvring. Maintenance dredging differs from capital dredging (which creates new or deepened channels) in that it typically removes smaller volumes of recent sediment deposits. However, maintenance dredging is conducted repeatedly over a port's operational life and cumulative environmental impacts can be significant.

Sustainable dredging practices encompass, among others, planning to minimize the volume and frequency of dredging where possible, selection of dredging equipment appropriate to site conditions and sediment types, use of low turbidity techniques such as cutter suction dredgers with closed pipe transport or environmental buckets for clamshell dredgers, timing of operations to avoid sensitive ecological periods (such as fish spawning or coral reproduction), and monitoring of water quality and turbidity during operations (PIANC, 2009; CEDA and IADC, 2018).

Depending on contamination levels, sediments may be suitable for open water placement, confined disposal facilities, or upland containment. Beneficial reuse options, where sediment quality is appropriate, include, among others, land reclamation, habitat restoration, beach nourishment, and construction material (PIANC, 2023).

The PIANC report Dredging Management Practices for the Environment (2009) and the CEDA IADC Handbook Dredging for Sustainable Infrastructure (2018) provide frameworks for environmentally responsible dredging. Key principles include, among others, early stakeholder engagement, use of best available techniques, adaptive management based on monitoring results, and emphasis on beneficial use of dredged material. The PIANC report Beneficial Use for Sustainable Waterborne Transport Infrastructure Projects (2023) provides guidance on the beneficial use of dredged material.

Major ports may conduct significant maintenance dredging programs and require long term management plans to ensure these programs are undertaken in a responsible manner. The Port of Brisbane in Australia has prepared a Long Term Maintenance Dredging Management Plan. As part of its program and spoil disposal management, its Reclamation Environmental Management Plan (EMP) sets out how most of the material used to fill its Future Port Expansion reclamation area will come from maintenance dredging (Port of Brisbane Pty Ltd, 2023). Beneficial reuse of dredged material is increasingly pursued where sediment quality permits.