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Author

• Dan Meigs

Abstract

Known as the Garden Isle for its picturesque beauty, Kauai is a 550 square mile island whose geographic centerpiece, the mile-high Mount Waialeale, receives more rain than any other place on earth. Potable water for the island is provided by a 100% ground water-based system operated by the County of Kauai, Department of Water (KDOW). The water system includes a series of wells, intake shafts (basically a sump that naturally fills with water which is equipped with a pump), and tunnels (basically free flowing ground water sources) organized into a number of hydraulically independent "zones." Each zone consists of one or more wells (including intake shafts and tunnels), tanks, and in some cases booster stations (tank-to-tank boosters as well as some in-line pressure boosting stations). The water system is distributed over a large geographic area providing water to population centers throughout the island. There are approximately 17,000 meters in the KDOW system and an average system demand of approximately 11 MGD. Ultimately, KDOW envisions a system with as many as 100 remote sites. From the present 81 sites, the system will grow six to seven sites a year for the next five years.

Designing a SCADA system to serve Kauai presented unique engineering challenges for Timberline Engineering. The remote sites are scattered throughout coastal regions, sugar cane fields, steep canyons and mountainous rainforest. Many of the remote sites are almost inaccessible making design and maintenance difficult. The rugged terrain and isolated hydraulic zones dictated a hierarchical system architecture, with each zone (or neighboring group of zones) equipped with a PLC acting as a SCADA submaster.

The submaster PLCs will communicate with their remotes over spread spectrum MAS radio systems. The submasters will collect field data from the remotes, perform supervisory control for the zone, and pass data to a SCADA host over a wide area network (WAN). To ensure the communications will be reliable, the system was designed with short, carefully engineered radio paths, repeaters where necessary, and an occasional telephone connection where radio was impractical.

The SCADA system must survive an island-wide emergency such as the category-five hurricane Iniki that devastated the island in 1992. To meet this survivability requirement, the system was designed to allow the submaster PLCs to operate the water system independently of the SCADA host and in the event of the failure of one or more of the SCADA submasters. The WAN was designed to allow high speed access between the submaster PLCs and the SCADA host computers under normal operation and lower speed connectivity over backup media when necessary.

The Water Department's Pua Loke complex in Lihue will be the site of the redundant host computers, historical database server, and six workstations. These workstations will receive system status and alarms from the SCADA host for the entire system. The automatic control of the system can be modified from the workstations and the system can be controlled manually from the workstations. The WAN will be interconnected with the KDOW business systems LAN for access and integration between SCADA and other applications as needs are identified.

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