Basin 2 is a former marine naval dock that covers an area of approximately 8 hectares and a relatively uniform depth of around 9m. The dock is surround by a mix of residential and commercial properties. The dock is managed by Chatham Maritime Trust who operate a water sports centre for a range of contact water sports. Given the use of the dock, that include youth water sports activities, a key management objective is to maintain a high water quality status to ensure protection of site users.
The dock displayed a range of management issues that impacted on its amenity function and water quality status. These included:
- Occasional development of ‘Red Tide’ algae blooms; and
- Deoxygenation of the lower water column during the summer months due to thermal stratification leading to water quality issues, restriction on marine ecology and development of hydrogen sulphide gas and odour.
An ISS-Flowthrough aeration system with 15(no) diffusers supplied with air from a single compressor was developed for the dock. The design of the system had to be such that it did not interfere with amenity use within the dock or its occasional use for mooring of large vessels. The primary purpose of the system was to provide complete mixing of the dock area to remove the negative impacts of thermal stratification on water quality conditions and marine ecology, together with preventing gas and odour generation.
The aeration system installation would be combined with a pre and post installation monitoring for Bathing Water Quality Standards together with measurement of in-situ physico-chemical measurements through the water column (i.e temperature, dissolved oxygen and salinity).
Water quality monitoring conducted in both pre and post aeration / mixing periods allowed the effectiveness of mixing to be established. The effects are summarised below:
- Microbiological Bathing Water Quality has been recorded as consistently excellent and no potential harmful algae blooms have been recorded since installation and operation of the aeration system;
- Mixing removed stratification effects and allowed good dissolved oxygen concentrations to develop in the lower water column;
- Marina fauna has developed down the lower dock walls and across the bed the dock where it was previously absent. The increased abundance of filter feeding organisms has resulted in marked increases in water transparency; and
- No odour issues have been reported since following operation of the aeration system.