and, because of this and the intervention of World War I, construction on the Cordeaux Dam was not commenced until 1918. In November of that year a Special Board of Experts consisting of engineers from the Public Authorities was appointed by the Government to draw up recommendations for the amplification of the Sydney water supply. This body not only endorsed the construction of the Cordeaux Dam but recommended the construction of the Avon and Nepean Dams as well. In 1921, three years after the Cordeaux Dam was commenced and five years before it was completed, the Public Works Department commenced work on a third and much higher dam at a site selected on the Avon River, a tributary of the upper Nepean. The Avon Dam was also designed and constructed by the Public Works engineers under the direction of the Chief Engineer for Water Supply and Sewerage, E.M. De Burgh. The resident engineer, during its construction, was Gerald Haskins. As with the previous dams, Cataract and Cordeaux, Avon Dam was built using cyclopean masonry. This consisted of sandstone blocks, quarried from the site, which were fitted into an irregular pattern and packed with sandstone concrete. However, in this case the rock was quarried to make a deep cut through a ridge to a neighbouring creek to provide the spillway for the dam. Like its predecessors, Avon also had the upstream face of the dam sheathed with a layer of basaltic concrete (2 feet thick) for watertightness and to resist wave and other erosion forces. The concrete was all manufactured on the site in special metal-crushing, concrete mixing plants. These included Jacques roll-jaw crushers, pulverising mills and Mullimix drum-type batchmixers. From the mixers, the concrete was discharged into concrete skips especially designed to facilitate the distribution of the concrete on the dam wall. All the plant was electrically operated and the current obtained from the State Power Station at Port Kembla by transmission lines in length. A road in length was constructed from Bargo railway station to transport all the materials. Other plant used on the site included two Lidgerwood cableways, three locomotive cranes and four stiff-leg type derrick cranes. All of these were designed and constructed in Australia. The water storage area for the dam was cleared of all timber and brush except for stumps high. Any hardwood timber of commercial value was cut into sleepers, fencing posts and rails