Lower Loddon Flood Studies
What are the Lower Loddon Flood Studies?
The main technical study for the Lower Loddon floodplain is the Flood Plain Management Study – Kerang to Little Murray (1986). The report proposed a series of works to manage the flood risk in the Lower Loddon.
The proposed works were not intended to increase the level of flood protection for the region. They were intended to modify the existing levee system to create a more reliable defence against floods and to prevent the need for future ad hoc levee development. This would reduce the frequency of flooding outside the strategic levees.
Two other flood studies have since been completed which build on the 1986 study.
These are the Kerang Lakes Flood Study (1989) and the Kerang to Little Murray Floodplain Management Plan – Assessment of Options (2006).
The early studies were completed by consultants for the Rural Water Commission, which was the State Government body responsible for floodplain management at the time, together with local councils.
The 2006 study was completed for the North Central Catchment Management Authority.
What did the studies propose?
The studies proposed a series of works to increase the security of the levee system, providing greater certainty in its level of protection.
Works included:
- upgrading the existing levee bank system to a consistent standard,
- removing obstacles, including other smaller levees, inside the levee bank system (i.e. cleaning up the main floodway),
- defining overflow sections 200-400 metres wide along the levee banks at 1975 flood levels and reinforcing these overflow sections
- removing severe obstacles to overflow floodways downstream of overflow sections, (i.e. creating secondary floodways)
- providing two outlets on the Murray River levee banks to enable the removal of floodwaters stored on the Lower Loddon floodplain, after the flood event.
Why were defined overflows proposed for the Lower Loddon?
The 1986 study recognised that large floods would break out of the levee system into the wider floodplain, even if levees were upgraded.
The study proposed to install overflow sections built to the 1975 flood level, (with the remainder of levees built at a higher level), to enable floods larger than the 1975 event to break out into the floodplain.
This would reduce the flood damage by appropriate land use planning along overflow floodpaths and reduce the chances of other protected areas being flooded.
The levee banks at defined overflows would also be reinforced to protect against floodwater erosion of the levee, and reduce the total volume of outflow.
Land downstream of a defined overflow would become a secondary floodway.
The flood studies proposed that these floodways would need to be wide and relatively unrestricted to ensure that the floodwaters did not concentrate and cause unacceptable downstream impacts.
Areas downstream of an overflow section would need to maintain a clear flood path, removing or adapting any existing obstacles such as roads and farm channels.
The secondary floodways that were proposed in the 1986 flood study were:
- From Pyramid Creek along Calivil Creek Drain to Barr Creek to Benjeroop Forest
- From Pyramid Creek along Kerang No.1 drain to Barr Creek
- From Benjeroop Forest along Duck Creek to Murray River north west of Benjeroop
- From Loddon River via the Winlaton Depression to Little Murray upstream of Fish Point
- From Loddon River to Reedy lake between Washpen Creek and the Murray Valley Highway
- Downstream of Third lake along Scotts Creek.
These overflow areas were not investigated in detail. The Pyramid Creek and Winlaton Depression overflows were investigated in more detail in later studies, but not implemented.
Do the flood studies propose works to remove floodwaters after the flood event?
The 1986 Study proposed two regulators to allow water to be drained into the Little Murray River at the bottom of the Loddon system. These works were not investigated in detail.
Why were the flood studies not implemented?
There are a number of reasons the 1986 and subsequent flood studies were not implemented.
1. The community did not accept the need for the proposals because they perceived a low flood risk. Some factors influencing this perception include:
- prolonged drought
- the practice of describing flood risk as a time interval, e.g. 1 in 30 year flood, which gave the impression that another flood would not occur for many years
- new landholders without memory of past floods.
2. The community did not accept the concept of defined overflows which would have adversely affected landowners downstream of the overflows along the floodpaths.
3. The proposed works presented a large undertaking and required a statutory authority to take ownership and develop a formal levee maintenance program. It was not sensible to install works on a levee system that was not being maintained to a consistent standard. No authority was obliged or tasked with this undertaking.
4. The subsequent studies in 1989 and 1999 determined that some proposed works, such as defining secondary floodways, were not feasible on such low lying land. Confining the overflow to floodways was also deemed undesirable because it would reduce flood storage to such an extent as to have adverse downstream impacts.
Other works, such as the larger regulator into, and out of, Kerang Lakes, were deemed technically sound, but too costly for the small flood mitigation benefit they provided.
What is the current status of the Lower Loddon Levees?
The existing levee system in the Lower Loddon is made up of a collection of private levees, built at different times and to differing standards.
They are considered to offer protection up to around a 1975 level flood, sometimes referred to as a 1 in 30 year flood for the region.
This level of protection is not reliable; the levees are very likely to fail in larger floods such as the January 2011 event.
The level of protection is thought to be reducing over time. This is because not all landholders maintain the private levees to the same standards.
The issues of levee ownership and maintenance in the Lower Loddon region are still unresolved.
The Parliament of Victoria Environment and Natural Resources Committee has launched a statewide inquiry into matters relating to flood mitigation infrastructure.
This will include identifying best practice and emerging technology for flood mitigation infrastructure and the management of levees, particularly the ownership and maintenance issues.
Does the Lower Loddon Irrigators Recovery Package aim to implement the flood studies?
The Package looked to the flood studies to understand the nature of the flood hazard on the Lower Loddon floodplain.
Even if the 1986 study had of been implemented, the region would flood at anything above a 1975 level flood.
The Lower Loddon region relies on protection from approximately 150 km of levee banks.
The cost of upgrading the levee bank system to modern standards is approximately $75 million. Every dollar of government funding spent protecting farmland on the floodplain, is funding that will not be spent on health, education or rural development projects.
The Package therefore aims to increase the resilience of the Lower Loddon community to flooding, by facilitating a change in land use to systems of agriculture and asset protection that are more compatible with the flood hazard.
This would achieve a fundamental reduction in the flood risk and degree of damage to property and peoples’ livelihoods.
The Irrigators Recovery Taskforce will consider a range of minor works that would compliment the aims of the flood recovery package.
