Level Of Lakes

Press, Volume CII, Issue 30213, 19 August 1963, Page 12

Level Of Lakes

The maximum level to which Lake Te Anau, the higher of the two lakes, may be raised is governed by the necessity to prevent the flooding of low-lying parts of the township of Te Anau. This has been determined by survey as 676.5 feet above mean sea level at Deep Cove, on Doubtful Sound, and corresponds to a reading of 20 feet on the lake gauge. Even at this level, some parts of the township are subject to flooding, to becoming swampy, and to carrying surface water. Because it would cost about £lOO,OOO to raise these areas clear of the water level, the company proposed in April, 1961, that it might be practicable to fix the maximum level of Te Anau at a lower point. While 676.6 ft remains the maximum legal level, it is intended under all but the most extraordinary circumstances. brought about by a flood of a magnitude such as would occur only once in 500 years, to control the lake a: a point about five feet below the legal maximum. This will substantially reduce, if not eliminate, the cost of raising the low-lying areas of the township. The bill before Parliament provides that Lake Te Anau can be controlled within a range of 20 'eel, from the 676.6 ft maximum to the lowest natural level of 656.6 ft. How ever, the normal operating range will be to the order of 15ft because of the normally lower maximum level. There is no indication in the agreement about how Lake Manapouri's level will fluctuate during the first stage of the power development, although the lowest permissible

level will be the natural low point of 575.5 ft above sea level at Deep Cove. Under natural conditions, the fluctuation is between 15ft and 20ft, and it is unlikely that the lake level will move outside this range under stage one conditions unless a major flood occurs.

When stage two of the power development is reached, and this may not be for several years, a dam will permanently raise Lake Manapouri, and another set of control levels will apply. For the practical reason of obtaining a fall or flow from Te Anau to Manapouri, the normal maximum level of Manapouri will be several, perhaps five, feet below the actual level of water in Te Anau.

This would place the normal top level of Lake Manapouri about 666 ft or 667 ft above sea level at Deep Cove. Once the lake has been raised to this new top operating level, it must not be lowered again by more than 27.5 ft. This means that the operating range of Lake Manapouri under stage two conditions will be between about 666 ft and 638 ft above sea level, an increase of between 62ft and 90ft above the present natural low level of the lake.