Wednesday, June 26, 2013

Australian Capital Territory — Thousands of Canberrans took a look at the new Cotter Dam on the Cotter River on open day on Sunday. The public was given limited access to the still-active construction site. Buses took viewers from the car park below to top of the dam wall. They ran every 15 minutes from 8:30 am to 4:00 pm.

The dam is to supply fresh water to the city of Canberra. This is to provide water security for the city as droughts become more frequent due to global warming.

It is a gravity dam, which holds back the waters through sheer mass. It is about 80 metres (about 260 feet) high. The dam is made from roller-compacted concrete. The concrete was laid dry and compacted with rollers. The concrete was made on site. Only the final touches use conventional concrete. In addition to the main dam, there are two saddle dams filling depressions in the landscape so flood waters flow over the spillway and not out the sides of the lake.

The dam on the Cotter River has been under construction for four years. Concrete pouring is expected to take another two weeks. The site is then to be rehabilitated. Thousands of seeds were collected during constructions. These are to be replanted to replace the native flora. Work is expected to be complete by September.

The dam replaces an old dam, first built in 1911 but subsequently expanded several times. Now heritage listed, it has been submerged by the waters of the new dam. Some materials were salvaged from the old dam to build the new, and some have been put on display.

The river is named after Garrett Cotter, an Irish-born convict who was transported to Australia and lived in the area in the 1830s and 1840s.