Dam Types and Materials
For dams of any but minor size the traditional building material in older countries has been masonry, later succeeded by concrete; these materials in appropriate structural forms have been associated with the development of sites favourable to their support and economy. Comprised in this group are dam forms designated as mass gravity, massive buttress or hollow gravity, arch and arch-gravity types (both simple and vaulted or domed), thin multiple arch and buttress, slab and buttress or Ambersen dams, typically in relatively narrow valley sites. Not all of these types are represented in New Zealand.
Expanding development in New Zealand has forced attention on the wider sites and on those less favourable in respect of rigidity and strength of foundation rock; hence there has been a significant general trend to the embankment type of dam built of soils, alluvials, and rockfills variously compacted. Nevertheless, in some countries (notably Spain, Portugal, Italy, and France), the economic use of concrete arch forms for wide valleys is favoured, provided there are no foundation weaknesses.
The bolder use of embankment types of dam, often of considerable height, has been conditioned to an extent by the modern expansion of the science of soil mechanics. Progress in the development of efficient means for the excavating, transporting, and compacting of rock and earth materials has also exerted a profound effect. Whereas costs of all other forms of construction have risen severalfold in money value, the costs of earth handling have been kept to much the same levels as in the days of the pick and shovel, and even in some cases, lower. Thus it is now possible to plan such projects involving earth-works on an unprecedented scale. Moreover, with the increasing difficulty of finding dam sites favourable to the traditional forms of construction, the development of this new method is timely. The Benmore power project on the Waitaki River is one instance. A site below the confluence of the Ahuriri tributary was preferable because of the greater power from the added inflow, but the Waitaki valley is relatively wide there and basement rock is not of good quality, thus indicating an embankment type of dam. To give some idea of the work involved, it may be stated that in operations associated with foundation excavations for required structures and construction of the main wall in rolled earth and other materials, more than 20 million cu. yds. were handled, yet in its economic aspect in relation to the power output, this project can rank as one of the most favourable in the country.
|Dams for Power—Clutha River|
|Purpose and Group||Power—Clutha River|
|Name of dam||Roxburgh||Hawea Lake||Kawarau|
|Location||..||..||Lake Wakatipu, outlet|
|Type||Concrete gravity||Rolled earth central core||Multiple piers and gates|
|Foundation rock or bedding||Schist||Weathered chlorite schist||Schist|
|Maximum height (ft)||180||98||..|
|Dam volume (cu. yd.)||..||560,000||Small|
|Spillway type||..||Gated undersluices||Gated weir|
|Discharge capacity (cu. ft./sec)||162,000||11,000||36,000|
|Reservoir area (sq. miles)||1·25||46||113|
|Effective storage volume (ac. ft.)||Small||2,000,000||500,000|