Lwandle surveys offshore discharge to determine achieved dilutions for their dense industrial effluents. The discharge and diffusers are located at a water depth of ±30 m off the KwaZulu-Natal upper south coast.
Two approaches are used – the first is the measurement of selected effluent properties through water sampling and analysis; the second is the direct measurements of added rhodamine dye concentrations through profiling of water column with a CTD sensor fitted with a fluorometer.
In a similar exercise off Cape Town we use turbidity to determine the dimensions of a domestic sewage discharge plume. The instrumentation employed includes CTD plus turbidity sensors and Acoustic Wave and Current beam intensity with the survey data being processed through Aquavision® software. The data shows that the buoyant effluent plume is being rapidly diluted into the receiving water body.
These applications demonstrate Lwandle’s ability in using technologies appropriate to the measurement and monitoring task at hand.
Lwandle conducts real-time monitoring of turbidity and dissolved oxygen concentrations for dredging operations e.g. with a Trailer Suction Hopper Dredger (TSHD) in the Port of Cape Town. This work employs an RBR data logger fitted with two OBS sensors for turbidity and one dissolved oxygen sensor.
The system is suspended from a surface communication buoy (GSM) with one of the OBS sensors at a depth of 3 m and the 2nd OBS a& dissolved oxygen sensor at a depth of 9 m. Measurement data is logged at ten minute intervals and transmitted to shore receiving stations on the TSHD, in the dredge contractor’s shore base and Lwandle’s offices ±8 km away.
This monitoring approach allows water quality thresholds to be set in terms of maximum permissible turbidity levels and minimum dissolved oxygen concentrations with an alarm system alerting the dredge master and dredge contractor when nearing these thresholds.
This allows immediate remedial action to be taken through reducing dredging rate, relocating or stopping dredging. The system is effective as at no time during the 6-month dredging programme were the set water quality thresholds transgressed.
This case study demonstrates Lwandle’s capabilities in deploying sophisticated water quality monitoring instrumentation and integrating these into communication systems, providing real-time data outputs enabling effective control of activities affecting water quality.
Lwandle participates in the tri-annual monitoring survey of the Chevron / Caltex oil refinery marine outfall that discharges into Table Bay on the Cape SW coast. For this survey Lwandle is responsible for sampling design, implementing the sampling programme, running the benthos analysis component and providing the interpretative report.
Geometric species abundance plots indicate that, at the time of this survey, there was no indication of disturbance to the benthos community at the sampling sites.
This study demonstrates Lwandle’s abilities in field investigations and, together with associates, providing integrated marine monitoring surveys, high quality analyses and clear results.
Old Warehouse, Black River Park, Fir Road, Observatory, Cape Town
PostNet Suite 50, Private Bag X3, Plumstead, Cape Town, 7801, South Africa