In order to efficiently and safely operate the Goulburn Murray Irrigation District, G-MW follows a set of operating guidelines.
Below are the operating guidelines for (click on the link to view the corresponding operating guidelines):
Operating Guidelines for Wanalta Creek Floodway and Cornella Creek Floodway at their intersection with the Waranga Western Main Channel
This is a summary of the Operating Guidelines for the operation of structures on the Waranga Western Main Channel where the channel intersects with the Wanalta Creek and the Cornella creek.
The guidelines are provided for information for the general public in the local areas of Wanalta and Colbinabbin.
Note: Comments in "Italics" are provided for explanation of the guidelines.
Wanalta Creek Floodway Operation (also called Groves Weir)
When substantial rains have fallen in the Wanalta Creek catchment area, monitoring of the creek by the Telemark for inflows into the W.W.C should be carried out.
- The Wanalta creek intersects with the Waranga Main Channel and in times of high flows on the creek, the structures on the Waranga channel are operated to direct the water either downstream in the channel, if it can be utilised, through the channel and returned to the creek to the north, if it cannot be passed down the channel, or a combination of both.
ACTION TO TAKE
1. During the off season, the Wanalta Floodway is to be set open to allow water to pass through the Waranga Western Channel (WWC).
- This refers to the period when the irrigation channel is not required to deliver irrigation water to customers downstream of this point. The floodway regulator is set to allow any inflows into Wanalta creek south (upstream) of the channel to pass through the channel to the north and continue down Wanalta creek.
2. During periods when the W.W.C has been filled but the District roster is not in operation, the Rochester Duty Officer/Waranga Western Operator is to monitor the creek and arrange action to be taken if it is expected that there will be a flow in the Wanalta Creek.
- This refers to the situation where the channel has been filled, but is not yet delivering water for irrigation. It is in a state of readiness for deliveries to commence.
3. When the District roster is in operation the creek is to be monitored by the Waranga Western Operator or the Field Operator who is on duty at Colbinabbin.
4. The door openings on the floodway regulator should only be enough to allow flow in the Wanalta Creek to pass through the Waranga Western Channel. The 3.6 metre SCADA door to be set in U/S mode to allow any increase in flows in the creek to pass through. IRRIGATION WATER IS NOT TO BE RELEASED INTO THE WANALTA CREEK.
- The key point here is the direction that there is to be no water currently stored in the channel passed into Wanalta Creek to the north. This ensures that the only water passed into the creek is water that has entered the creek to the south of the channel. The reference to the SCADA door is a door that operates automatically to keep the level in the channel constant and this allows initial flows in the creek to pass through the channel and is utilised prior to operating the manual gates.
5. Action should be taken to shut off releases from Waranga Western Headwork's and lower the Channel.
- The intention here is to reduce flows from the Waranga basin and is the first action taken. The lowering of the water level in the Wanalta pool of the channel will depend on a number of issues. These being; can water be transported past Cornella Creek at Colbinabbin, if this creek is also in flood then water cannot be passed downstream and the channel level may remain at a higher level than would be preferred. Other issues to be considered are; if there is still irrigation demand and can the water entering the creek be used to meet this and reduce impact on landowners to the north of the channel, can water be passed to Greens Lake or further west to the Tandara pondage.
Cornella Creek
Monitoring of Cornella Creek can only be carried out visually when high flows are in the creek. The creek will over flow into the Waranga Western channel.
- There are no monitoring devices on the Cornella creek to the south of the Waranga Western Main Channel and all information is from visual inspection and reporting. In high flows the Cornella Creek can overtop the Waranga Western Main Channel bank in three locations and exit in 4 locations that are designed into the channel banks.
ACTION TO TAKE
1. Regulator on W.W.C at Colbinabbin to be closed off.
- The regulator on the Waranga Western Channel (W.W.C) located just north of the Colbinabbin Township is to be closed off to prevent flood water passing down the channel until all the channel system is operating in a safe mode. The closing of this regulator takes place after the water level in the channel has been reduced to the sill level of the doors on the Cornella Creek siphon. This is to prevent the passing of water stored in the channel being passed into the Cornella Creek to the north.
2. Doors on the Waranga Western Channel at the Cornella Creek Siphon, should be fully open.
- The opening of these doors allows any water that enters the channel to flow out into the Cornella Creek to the north. They also allow water that backs up from obstructions in the creek to enter the channel and therefore assist in mitigating the impact on the land immediately to the north of the channel.
3. Floodway doors on the Waranga Western Channel bank, east and west side to be removed. (Total of 78 doors each side).
- These doors are required to be removed manually and are removed to allow the overland flow of water from Cornella Creek to enter the channel via the floodway on the south bank of the channel and exit via a similar floodway on the north bank.
On occasions it may be possible for water from a Cornella Creek flood to be passed down the Waranga Western Channel and disposed of in an alternate location. There are a number of criteria that need to be considered prior to this occurring. In all cases the first actions are as described above in the actions to take under Cornella Creek guidelines. The following are the guidelines to be followed to determine if water can be transferred.
Lake Cooper and Greens Lake Operating Rules
This is a summary of the Operating Guidelines for the operation of Lake Cooper and Greens Lake.
Note: Comments in "Italics" are provided for explanation of the guidelines.
ACTION TO TAKE
1. When possible water from Cornella Creek can be diverted into the Waranga Western Channel for disposal to the Campaspe River, Greens Lake or Lake Cooper (in this priority order).
- This order was determined a number of years ago and is intended to reduce operating costs for G-MW and Customers when assisting with flood water removal.
Diversion of water cannot occur when - The Waranga Western Channel is being used for water supply or maintenance work is being carried out.
- Diversion cannot occur if the guidelines and trigger levels below will be breached.
- Water cannot be diverted to the Campaspe River if the river is at or above minor flood level.
2. Water can be released from Lake Cooper to Greens Lake when Lake Cooper water level is above 105.00 A.H.D and Greens Lake is below its target level or Lake Cooper is about to spill. (Maximum height for Greens Lake is 102.20 A.H.D)
- The target level for Greens Lake is not fixed and varies on the time of year/season. The target level is much higher in spring than in late autumn leading into the winter period.
3. Releases from Lake Cooper to Greens Lake are limited under normal conditions to maintain the Waranga Western Channel salinity to 300 EC or less when Greens Lake pumps discharge into the Waranga Western Channel or releases may occur when Lake Cooper is about to spill.
- This refers to the need to ensure that water pumped from Greens Lake for use by irrigators and urban authorities does not exceed a salinity level that would adversely affect their operations.
4. Some Waranga Western Channel water destined for Greens Lake can be released into Lake Cooper with the release of the same volume of water from Lake Cooper into Greens Lake so that Greens Lake does not exceed 1000 EC.
- This ensures that water quality in Greens lake is not adversely affected by high saline water from Lake Cooper and therefore impacting on the ability to use Greens Lake to supplement supply for customers in high demand periods for irrigation.
5. When Lake Cooper is about to spill from the Northern end into Greens Lake, the Link drain can be used to pass some or all of the spill to avoid unnecessary overland flooding through Corop.
- If Lake Cooper is about to spill G-MW may take the decision to move water to Greens Lake to make Lake Cooper safe even if the above guidelines may be exceeded.