Charleston Dam Detailed Design

Water security for the North has taken a momentus step forward following the announcement of funding for the Charleston Dam in the Georgetown/Forsayth locality.

CDM Smith was engaged by Etheridge Shire Council (ESC) to conduct topo­graph­i­cal survey, geot­ech­ni­cal inves­ti­ga­tion, detailed design and construc­tion management services. CDM Smith managed and led the detailed design component of the project with structural design, survey and geot­ech­ni­cal inves­ti­ga­tion in put provided by a subcon­sul­tant.

The purpose of the Charleston Dam is to supply town water to Forsayth via a pump and pipe arrangement and to Georgetown via release of stored water from the dam to replenish the river bed and sand aquifers. Georgetown will extract water via an already operating spea system in the Etheridge River, downstream of the confluence with the Delaney River: Based on projected  future demands, (demand and yield assessment conducted by others) a 6,700 ML storage volume provides 95% reliability of yield.

A hardfill dam embankment was concep­tu­alised by CDM Smith over the original earth embankment concept design (by others) as no clay borrow source was identified within a cost effective haulage distance. Trial mixes consisting of local weathered granite material were formulated with test results confirming suitability for construc­tion of a hardfill embankment. This approach avoided the need to open a quarry to source large volumes of aggregate and signif­i­cantly reduced the cement volume required compared to a mass concrete or roller compacted concrete embankment.

The Charleston Dam design was designed in accordance with guidelines produced by the Australian National Committee on Large Dams (ANCOLD). In accordance with the guidelines, Charleston Dam was classed as a High C hazard dam and a 1:10,000 Annual Exceedance Probability (AEP) acceptable flood capacity applied.