Managing reservoirs

To ensure the best quality water is selected from its storages, the SCA uses a number of quality management processes including:

  • selecting water from different reservoirs
  • selecting water from different levels in the storages
  • destratifying reservoirs, and
  • monitoring water quality and analysing trends.

Water in storages settles into layers through a process called stratification. The layer properties often vary dramatically because of differences in temperature, light, density and oxygen.

Temperature is an important indicator of water quality. The SCA's storages are monitored by thermistors; equipment that records temperatures at different depths within our dams.

Water flowing into storages from the catchments (inflow) will settle at the level of the same density. By monitoring the inflow, we predict where the incoming water will settle. Off-takes can then be selected from levels away from incoming waters to maintain quality.

Running down the upstream face of Warragamba Dam are three offtake chambers. Screens are placed at varying levels, depending on the result of water quality tests and analyses. Water flows through the screens from the chosen level into the water supply pipelines for distribution to our customers.

In smaller storages, artificial destratifiers (aerators) may be used to keep stored water circulating and to reduce the chance of low oxygen levels in water in the bottom layers. This helps to maintain good water quality by preventing metals from becoming soluble. Soluble metals can be a problem because they may not be eliminated during water filtration processes and may cause aesthetic problems such as taste, odour, or stained washing.

Late in winter, lakes experience a phenomenon known as turnover . This occurs when surface water temperature matches that of the cold water at the lake's bottom. The surface water is displaced by the bottom water as the water column inverts (turns over).

SCA Water balance for total supply system 2006/2007

The SCA's operating licence condition 6.4.2(b) requires the SCA to provide information to the Independent Pricing and Regulatory Tribunal (IPART) by 1 September each year for the previous financial year on the water balance. It also requires the SCA to make this information available to the public.

The water balance for the individual water supply systems listed below and the total system use the methodology developed by Sinclair Knight Merz for IPART.

  • Warragamba
  • Woronora
  • Blue Mountains
  • Shoalhaven
  • Upper Nepean

Sources of Water refer to water entering each system during the year, including inflows. Distribution of Water describes water leaving the system including extractions, environmental flows, releases and spills.