Environmental management of marine reclamation works helps manage impacts of dredging and ensures that a project’s quality objectives are met. To achieve satisfactory environmental standards, a comprehensive Environmental Monitoring and Management Plan (EMMP) should be developed. This can incorporate feedback – also known as adaptive – monitoring which will allow work to continue as adjustments can be made in real time.
A first step in managing a dredging project is the Environmental Impact Assessment
(EIA). The Environmental Impact Assessment establishes a baseline record of the nearby areas in the water and on land. The parameters of the original conditions must be carefully monitored once dredging begins.
Changes in the surrounding waters and sand can be observed and measured. Turbidity
levels and dredging plumes are also monitored. Feedback monitoring
records these factors and allows adjustments to be made during the course of the project. Compliance monitoring
involves whether the owner and contractor are abiding by such things as seasonal windows for dredging or the depth that has been stipulated to be dredged in a waterway.
Parameters for feedback monitoring
Some of the parameters to be monitored by feedback monitoring are:
- turbidity levels in areas where sand is being discharged, taking into consideration the direction of currents and tides in relation to the the natural environment;
- the amount of total suspended solids (TSS) in the tailwater;
- physico-chemical factors such as dissolved oxygen, pH, temperature, salinity and conductivity;
- hydrodynamic conditions including current velocity and direction, wave height and direction
- variations in tides;
- meteorological conditions such as wind velocity and direction, temperature and humidity, barometric pressure and precipitation rates of sedimentation and erosion.
A compliance monitoring programme aims to ensure that the dredging process complies with legally or contractually stipulated restrictions. Restrictions can be either physical, for instance, the dredging depth, location or transport mode, limitation on turbidity or sedimentation rate at a vulnerable site nearby, or seasonally related such as special restrictions during breeding season, or quality oriented. These restrictions can vary markedly from one project to another.
Dredging in sensitive habitats
Environmental management of marine reclamation works close to sensitive habitats may need to provide a higher level of control than in less sensitive areas. For instance, visual inspection of the mangrove
areas and coral reefs
during dredging activities may also be necessary in addition to other forms of monitoring.