Design of an elastic mooring for remote turbidity monitoring buoys

In December 1996, the Greater Vancouver Water District (GVWD) contracted to METOCEAN the design and development of special, instrumented buoy systems to remotely monitor changes in fresh water turbidity of city reservoirs in the vicinity of Vancouver, British Columbia, Canada. Typically, these buoy systems consist of a central buoy supporting an RF telemetry link and a data line with two turbidity sensors located one near the surface and one near the reservoir bottom. This buoy is held on station with an elastic bi-moor. Three smaller buoys to service the data line and set/recover the bi-moor legs complete the system. This paper first reviews the environmental requirements and specified design criteria. The large range of water level variations, the necessity for providing clear spacing under the telemetry buoy for the sensors and the data line, and the presence of occasional strong currents at the time of gate openings, led to the selection of a bi-moor as the most desirable mooring configuration. Rationales for the selection of a compound mooring partly made of elastic cord and partly made of chain to fabricate the bi-moor legs. Methods of analysis for their design, and description of the main components of these moorings are nest presented. The paper then addresses the telemetry components of the system. Data are collected from the turbidity sensors and telemetered via RF link to a receiving station at the reservoir dam. These data are then transferred to the GVWD SCADA system for evaluation and action as required. The implementation of the bi-moor and associated service buoys required careful planning and execution which are summarized nest. Finally, the paper concludes with a short description of other potential applications for similar buoy systems.