The Bacchus Marsh Basin is an alluvial flood plain where the Werribee and Lerderderg Rivers meet, just above the Melton Reservoir. To the north, west and south the basin is bounded by lava flows. 1 Also joining the Werribee in the basin are the Parwan and Pyrites Creeks.
The Werribee crosses the basin from north-east to south-east, where it has eroded an exit from the basin through the Bullengarook lava flow.
Until the early 1900s the Lerderderg River joined the Werribee after passing through a wide swampy area. However municipal leaders at that time decided to construct a channel across the basin through which the Lerderderg should flow, and it has remained in the channel ever since, joining the Werribee at their present confluence.
The basin is at the base of the Victorian Uplands from where much of the its fertile soils have come as a result of erosion of creeks and rivers, losing much of their own soil and structure and causing the resultant silt to be deposited 0n the Bacchus Marsh floodplain. In the 1948 report entitled ‘Erosion on the Melton Reservoir Catchment’, an investigation seeking causes and extent of the erosion of the catchment of the Melton Reservoir, it was noted that:
“It is this natural, large-scale erosion which has formed the Bacchus Marsh flats and has placed the good soils on
the Werribee Plains.”1
Dominant crops in Bacchus Marsh are: Vegetables - loose leaf lettuce and broccoli, while orchards grow mainly apples. These have an annual value of about $16M and there is considerable value-adding prior to market - particularly in the specialty salad crops - with total sales turnover of $55M.2
It is in the easterly section of the basin that the Parwan Creek and Lerderderg River join the Werribee, and then the river is also met by Pyrites Creek (also known as Coimadai Creek) and Djerriwarrh Creek. The combined waters then flow into the Melton Reservoir.