POSSIBILITIES OF EARTH DAMS BEING INVESTIGATED NOW

Bay of Plenty Beacon, Volume 14, Issue 28, 22 August 1949, Page 7

POSSIBILITIES OF EARTH DAMS BEING INVESTIGATED NOW

Although the earth dam has been used to a considerable extent overseas, it is only within recent years that fairly large-scale projects have' been attempted in New Zealand. These have been rendered possible, as in other countries, by the availability of modern earth moving and compacting equipment, and the necessary technical knowledge required to select suitable types of soil and handle them correctly on the job. Old-time methods of building earth dams are not sufficient to enable the large structures demanded for present-day metropolitan water supply or hydro electric schemes to be built with assurance of success.

In these days of shortages of cement and skilled labour for placing concrete, the earth dam gains favourable consideration. Further, where the foundations for the dam are poor, the earth dam is a virtual necessity. On the other hand, where the foundations are good, but available soil is not of the most suitable type, the earth dam may not be worth considering. The climate and topography of the site must also be taken into account. Earth dams may also be used as adjuncts to concrete dams in a water storage scheme.

Earth dams are rarely built of homogeneous . material. The usual type consists a core of fairly impermeable soil, flanked on either side by more pervious but structurally stronger materials, such as sands and gravels. The essence of construction control is to place all materials in such a manner as to render the dam as watertight and as strong as needed. On large projects a-small control laboratory is a necessity.

The Soil Physics Section of the Soil Bureau, Department of Scientific and Industrial Research, is engaged as part of its activities in testing soils to find their suitability for earth dam construction. Past and present projects where the services of this section have been called in are the Lower Nihotupu earth dam (which provides additional storage for the Auckland City water supply), lake level control schemes at Pukaki, Hawea and Wanaka, and proposals for earth dams on rivers at Whakamaru and Atiamuri (Waikato), Roxburgh (Clutha) and Cobb Valley (Nelson district). The Soil Bureau staff have also assisted in the development of job control methods and the training of personnel for field laboratories.