Managing Floods in NSW

In a country that has a long history of Droughts and Floods we should have taken better notice of what that has meant and then to act in a manner that does not build assets in flood prone areas unless wise planning is carefully considered. We have not done this well at all in the past, and it will be difficult to re-jig things to protect assets from future floods; however, there are some important things that must underline all that we as a state do and they are simple yet not easy to correct or to implement.

Assessment:

• Every river has a natural flood plain some that are clearly seen but others are not as clearly seen.
• When a river in a drought time the river will retreat to very little water in the river valley, and during drought times this may give confidence that there are limited flood possibilities in certain areas that will, unfortunately, actually flood when the prolonged rains come.
• In NSW the rainy periods are very changeable and as such there is not a consistent single rainy season, as such as some may suspect.
• It is not unusual in NSW to have significant and prolonged rainfall during any month/s of the year; however, equally dry rain free month/s may occur during any month/s of the year and to be extended for several rain free months.
• Heavy and persistent rain fall may occur either in a small area of the state or be widespread throughout the whole state.
• Many rivers are very long and connected to many streams that may often be dry except during significant rain events; therefore, as such a river may flood a drought area due to heavy rain in the upper reaches of the river catchment.
• Floods are caused by excessive water in the rivers and streams, so flood prevention would essentially be managing the amount of water in the rivers and streams, with a view to remove the excess water as is appropriate.
• On river dams do not remove excess water from the river or streams but rather back up the water behind the dam wall, while off river dams do remove water from the rivers and streams hence can reduce the threats of flooding if sufficient water is extracted for the river system.

Policy:

• Storage of water via on river dams may be an easier engineering plan than off river dams yet only the off-river dam will extract water from the system so as to prevent flooding during high rain events, so are to be preferred wherever possible.
• As it is possible to have multiple very heavy rain events in one area of the state while drought or near drought conditions will be happening in other places in the state the capacity to move significant amount of water from one part of the state to another at high volumes is very necessary to establish
• Interconnection of the dams is important to manage the storage of water to maximize the amount of water that can be extracted from a river system as required
• The recent heavy rain events in NSW are a part of normal cycle changes to the climatic conditions in NSW and therefore, we as a state must take action to prepare for future similar events that can be expected again and again
• All areas that have faced recent flooding need urgent assessment so as to discover how to create a plan to remove excess water out of the river system via off-river dams, and any other action to protect assets and peoples’ homes and businesses.
• After the assessment urgent action must be to construct off river dams sufficient to remove excess river water from the rivers.
• Levee banks are not the presumed solution that has often been put forward by some experts; while levees may contain water in a river they cannot assist when heavy widespread rain occurs outside the levee bank, and in these circumstances may make the flooding far worse outside the levee bank.
• Wherever possible on river dams need to be assessed as to whether it is possible to make them into an off-river dam.