The study area covers the floodplain of the Lachlan River from Lake Brewster Weir to Whealbah Bridge. The length of the Lachlan River channel in the study area is about 170km. The river is highly sinuous, and the hydraulic capacity of the channel is exceeded in major flood events, leading to extensive floodplain inundation. The study area also covers the floodplains of several creeks which function as effluent streams from the Lachlan River. They include the reaches of Willandra Creek, Yangellawah Creek, Middle Creek and Merrowie Creek extending from the river to the disused Hillston-Roto railway line, and the reach of Cabbage Garden Creek extending from the river to Whealbah Road. In addition, overflows from the left bank of the Lachlan River into Gum Swamp are included in the study area.
A good understanding of flood behaviour between Lake Brewster Weir and Whealbah will be an important precursor to preparation of both the rural and urban plans. Accordingly, a flood study has been undertaken with main objectives as follows:
- To compile and assess available data relating to flooding in the study area;
- To define the nature and extent of the flood regime in the study area, including estimation of flood flow distributions;
- To develop a hydraulic model with capability for modification and enhancement to assess the hydraulic impacts of floodplain management options for both the rural and urban areas;
- To provide detailed information on flood behaviour in the vicinity of Hillston for floods with various annual exceedance probabilities (AEPs), as well as for an extreme flood event.
