During the mid 1970’s Sydney’s water supply was assessed as inadequate for Sydney’s growing population, so with the assistance of the Snowy Mountains Hydro-Electric Authority the Shoalhaven Scheme commenced construction. The scheme was designed to supply local communities and to supplement other Sydney's storages during times of drought.
Water is also released from Tallowa Dam into the Shoalhaven River to enable the Shoalhaven City Council to extract water from the river to supply Nowra.
River health & environmental flows
Environmental flows from Tallowa Dam to the lower Shoalhaven River ensure more water is protected for the health of the river.
The new flow arrangements reflect the significant work to assess river health needs. They replaced the interim flow rules, which were in place since 1999, where up to 90 million litres of water was released daily from the dam for the health of the Shoalhaven River.
The new environmental flow rules, which commenced in mid-2009, contribute to improving the health of the lower Shoalhaven River by:
- Ensuring more water is released for river health particularly during times of low flows
- Better mimicking the natural river flow for the benefit of native plants and animals.
The new rules for environmental flow releases from Tallowa Dam to the lower Shoalhaven River are:
- All dam inflows less than or equal to the 80th monthly inflow percentile will be passed through the dam to protect low flows in the river downstream
- 20% of dam inflows greater than the 80th monthly inflow percentile will be passed through the dam to protect a portion of medium and high river flows downstream
- Contingent or special purpose flow releases will be made from the dam to manage identified river health issues downstream, such as in periods of drought when the minimum operating level of the dam may be lowered to three metres – such releases will be determined in consultation with affected parties.
This water protects one hundred percent of critical low river flows. Medium flows will be partially protected and a large proportion of high flows, which flush the river, will continue to flow over the dam wall. When Tallowa Dam is full, inflows will continue to spill over the dam wall.
The WaterNSW and DPI Water monitor assess and report on the effectiveness of the environmental flow rules and reports and made publicly available.