Onehunga Bay Reserve in Auckland, New Zealand, provides its residents with both marine and land facilities. One of them is a recreational sea water pool that serves as a natural pool for swimming and water sports, and a private docking place for small yachts.
Onehunga Bay is part of a group of islands surrounding the city of Auckland. Owing to its proximity to the South Pole, the bay is heavily influenced by tidal occurrences. Two years ago the bay was closed off by a motorway built across it, forming a pool 350 x 150 x 2m (1,148 x 492 x 6.5 ft). This recreational pool serves as a small harbor for yachts and a swimming area for families living nearby. In order to sustain an acceptable level of sea water in the pool, Auckland City Council had to convey water in pipes positioned under the motorway. The City Council sought a solution that would monitor the level of sea water inside the pool to prevent low-tide situations that would leave the yachts and other marine vessels exposed. To keep an acceptable level of water in the pool during low tide, an electronic gate was installed at the entrance to the pool, which was closed before the water level started to decline. The amount of water in the pool was maintained until the tide was high again, and the gate could be opened. For this, the council had to employ a special maintenance person responsible for opening and closing the gate as necessary, by using a mechanical float meter as an indication. This proved to be inefficient since these mechanical devices can not provide accurate readings and also tend to wear and tear in time. An immediate electronic substitute was needed - one that would keep check on the tide level and activate the gate 24/7.