Grafton Sewerage Reuse Assessment

The Grafton Sewerage Strategy adopted by Clarence Valley Council in November 2000 included:

• an urban reuse pipeline from North Grafton STP for irrigation of the local racecourse, golf course, appropriate parks and gardens on route as well as potential residential and industrial reuse;
• decommissioning South Grafton STP and transferring sewage to Clarenza STP; and
• investigating opportunistic agricultural reuse along the current discharge pipeline from Clarenza STP to the Clarence River.

LRAM was commissioned by Council to lead feasibility investigations into urban reuse at North Grafton and agricultural reuse at Clarenza. Specific tasks undertaken by LRAM were:

• consulting with potential users regarding their interest in utilising recycled water for beneficial reuse;
• identifying and mapping soils within the potential reuse areas;
• assessing the suitability of these soils for irrigation;
• undertaking detailed water balance, nutrient and salt modelling;
• highlighting implications for irrigation design;
• identifying potential environmental impacts from irrigation; and
• preparing design concept plans for both schemes.

For North Grafton, the study found that the STP has sufficient flow to meet average and peak demands for irrigation of all open space areas and schools and for residential reuse in garden watering and toilet flushing along the distribution main. However, maximum average annual demand represents only 20% of the projected recycled water supply available in 2006.

Water balance modelling results for North Grafton

The Clarenza study concluded that there is sufficient annual flow of recycled water to provide an annual water allocation of 6 ML/ha to 150 ha of irrigation on the Clarence River flood plain. However, the storage capacity would need to be enlarged to at least 100 ML from the current 36ML dam at the STP to provide an annual security of supply of 65%.

Effect of storage size (BSD) on reuse potential at Clarenza

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