Six Return Water Quality Fast Facts

in2Dredging (i2D) has launched its own tool for predicting the quality of return water. The Return Water Quality (RWQ) model generates a particle size distribution and follows the settlement of each particle size along the length of the sand fill (reclamation area) and/or sedimentation (settling) basin.


Port Brisbane reclamation area sand fill and sedimentation basin area return water quality
Port Brisbane sand fill and reclamation area


i2D releases the following six Return Water Quality fast facts to promote the release of the new RWQ model:


  1. The length of the flow on the sand fill and/or sedimentation basin has to be long enough to allow the sediments to settle.  The width and depth of the sand fill and/or sedimentation basin has to be large enough to minimise the flow velocities.

  2. Nephelometric Turbidity Unit (NTU) is often the norm used to measure return water quality as it can be easily and immediately measured in the field. Measuring total suspended solids in mg/L takes more time and effort as samples have to be sent to a lab.

  3. Correlation between NTU and mg/L can typically be established, but this correlation is site and time specific. Each project has a unique correlation.

  4. Background conditions have to establish the natural turbidity levels without any interference from dredging activities. Take into account seasonal variability and extreme events, such as rainfall, cyclones and storms.

  5. Surface waves in the sand fill / sedimentation basin can resuspend sediments. Ideally, the length of the sand fill is limited in the predominant wind direction to reduce the fetch length and therefore the surface wave height.

  6. Flocculants might be an option, if significant amounts of clayey materials are present, if the area for the sand fill / sedimentation basin is limited, or if the environmental water quality requirements are stringent.


in2Dredging’s consultants take immense pride in our advanced tools.

Read more on our Return Water Quality (RWQ) tool