Flow in the Coliban River below Malmsbury Reservoir is regulated by the operation of the Malmsbury, Lauriston and Upper Coliban reservoirs. An important distinction between the Coliban River and other regulated Victorian systems is the lack of irrigation demand that may be met by managed releases downstream of system storages. Flow in the river is influenced by the passing flow entitlement, which depends on catchment inflows and major flood events in the catchment.
The VEWH does not have any environmental entitlements in the Coliban system, but the passing flow can be managed – for example, it can be accumulated and released when most needed – to help mitigate some risks associated with a critically
low summer/autumn flow, including low oxygen levels in the river between Malmsbury Reservoir and Lake Eppalock. A small volume of Commonwealth water for the environment is held in the system but has a high delivery cost. There is no plan to use the water in 2023-24.