Bullet-proof buoy solves level-measuring problem

It saves manpower and can even cope with a complete lack of any electrical or telecoms infrastructure. Peter Easey of MetaSphere reports on a new vandal-proof approach to reservoir level measurement

MetaSphere has helped Yorkshire Water in its development of a new approach to reservoir level measurement. As well as removing significant manpower demands, the new system also copes, in some installations, with a complete lack of any electrical or telecoms infrastructure in its ability to provide measurements far more regularly than before.

Just to complicate the design process, as well as coping with the adverse environmental demands, the level-measuring telemetry buoy also has to be shotgun and air pellet proof to cope with vandalism.

Yorkshire Water has 105 impounding reservoirs, which must have their water level checked and recorded once a week by law (Reservoirs Act 1975). These reservoirs must also have safety checks and general maintenance performed on them, often also conducted on a weekly basis.

As part of its weekly operation, the company runs a Water Resources Allocation and Planning (WRAP) programme weekly that determines which sources of water should be utilised and which water treatment works should treat it. For the plan to run effectively, all the reservoir levels must be known by the same day of each week, a task which, prior to the introduction of the new system, required the Raw Water Head Works team of about 30 people to visit all the sites the previous day to make manual readings.

From 1990 onwards, of the 105 reservoirs, some 65 were fitted with mains power, PSTN communications and submersible pressure transducers or ultrasonic sensors, the primary requirement at that time was only to know if the reservoir was overflowing. A survey of the sites in 2006 found that only a minority of the 65 sites was producing accurate telemetry data - which could subsequently be used by WRAP.

Yorkshire Water realised it needed accurate level data from all reservoirs at least once per day. For reservoirs with a flat-face dam or suitable structure (like a valve tower) in the deepest part of the reservoir it is often possible to measure depth by locating ultrasonic or radar sensors directly over the water. This data is then collected using a MetaSphere MM3P RTU and communicated to MetaSphere Master Control data gatherers.

For reservoirs with no suitable structures a new approach was required and subsequent R&D work led to the development of a telemetry buoy. The Yorkshire Water telemetry buoy uses a submersible pressure transducer anchored one metre from the reservoir bottom with a cable linked to the buoy on the surface. The buoy's sealed enclosure houses a battery-powered MetaSphere MM3P RTU with an integrated GSM communications module.

The unit is programmed to wake up every six hours to take a depth reading lasting 45 seconds. Then, every 24 hours, it sends the four readings by GSM to the MetaSphere Master Control data gatherers. The RTU batteries also supply the 24V loop power for the sensor and have been designed to have a minimum life of three years.

In developing a practical solution a number of important issues had to be taken into account:
  • The unit had to be completely waterproof
  • The batteries had to be protected from freezing temperatures, yet had to be easily accessible.
  • The unit had to be secure against unauthorised access
  • The unit had to be shotgun and air pellet proof to cope with vandalism from the shore and from boats
  • It had to be easily transported and installed
  • All equipment had to be light enough to be manually lifted
  • It had to be easily installed and configured
  • The buoy needed ballast due to its weight and it needed anchoring
  • It had to be cost effective
The MM3P RTU is a critical component in the solution, designed from the outset as a low-cost, fit-and-forget unit for use in harsh and hazardous environments and remote locations.

Testing throughout 2005/6 has proved that Yorkshire Water has a range of practical and reliable solutions for reservoir monitoring, and it is rolling out level monitoring to more than 100 reservoirs. The cost for the telemetry buoy solution, including installation, is less than £5,000.

Freed from the cyclic reading duties, the Raw Water Head Works team can optimise reservoir-visiting schedules by completing manual level monitoring, safety checks and maintenance work in one visit.

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