Saturday, March 6, 2010

Wyangala Dam

Although designed and built to the highest standards at the time, the original dam had shortcomings by today's standards. There were fears it could be subjected to unacceptably high stress by floods greater than those the spillway was designed for.

Investigations showed that raising the crest level of the dam by 23.5 meters would increase the storage capacity by almost four times. This worked out to be cheaper than building alternative storage on a Lachlan River tributary, as the enlargement work was carried out at the same time as strengthening the original structure. Work began after a Parliamentary Act was passed in 1961.

In 1971, the work was completed. The new embankment, built immediately downstream of the original wall, was made of rock fill with an earth-filled core.

A new spillway capable of withstanding a very severe flood was constructed, and a road bridge was built over the spillway. Outlet works were included in the design, with one low level and one high level outlet.

I have examined many of the remains of the old construction sites - where the granite rock was quarried and how it was moved, the concrete mountings that are all that remains of the cranes and steam powered engines and I will show more of these later on, as well as some historic images of the construction period.  There is even an old cemetrty located some kilometres away that I am yet to investigate, however, its remoteness is said to relate to the workers superstitions of having the dead too much in view.

The design provided for a power station to be built downstream if it was required in the future.

Storage capacity: 1 218 000 mega litres
Surface area: 5 300 hectares
Catchment area: 829 000 hectares
Annual regulated flow: 490 000 mega litres
Crest length (excluding spillway): 1 372 meters
Maximum dam wall height: 82.3 meters
Maximum width at base (including old dam wall): 304 meters

(Extracted from "More Than a Dam - Wyangala" - originally presented by The Department of Water Resources.)

This view was taken from the northwest, and shows the rear of the dam wall in the middle distance, with the coffer dam (normally completely submerged) immediately to the right. The picture dates to July 2003, and shows the effects of sustained drought on Lake Wyangala, which stops several kilometres short of the main spillway.

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