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Goulburn Murray Water is responsible for the day to day operation of the Yarrawonga Weir on behalf of the Murray Darlin Basin Authority. 

General

Yarrawonga Weir is the largest of the Murray Darling Basin Authority's 16 weirs.

Construction

Construction began early in 1935 and was completed in 1939. The weir has raised the water level in the river so that that the gravity diversion is possible via major channels to irrigate land in both New South Wales and Victoria.

Water impounded by the Yarrawonga Weir forms Lake Mulwala, with a capacity of 117,500 ML covering an area of 4,400 HA. The full supply level above the river bed is 14.2 meters and 124.9 meters AHD.

Yarrawonga Weir is also used to a limited extent for flood mitigation. Releases can be made before the arrival of flood water to help level out the flood peak and reduce the flood effects downstream.

Regulating Structures and Embankment

The weir contains two reinforced concrete regulating structures. The design is that of a Regulated Ogee Crest Spillway with a total of ten, 12.2 x 6.1 meters steel gates, attached to concrete counter weights via a cable and pulley sheave assembly. Each gate weighs about 40 tonne. The steel gates are lowered and raised by electric motors located on the steel truss above the structure. 

The weir consists of three sections. The first is the “Southern Regulating Structure” which is 116 meters in length and is located across the river channel. This concrete structure is the main regulator in the weir with 8 vertical lift gates. 

The second and middle section is an earthen embankment separating the regulating structures, consisting of a clay core with steel sheet pilling, covered by selected earth fill shells faced with hand-placed concrete pavers. The earthen embankment extends 270 meters across the river flats, approximately 7 meters in height with an 8 meter crest width.

On the northern side of the weir is the ‘Northern Regulating Structure’, which is 30 meters in length, has 2 steel flood gates and is used to regulate and pass higher flows during floods.

There is another short earthen embankment at the north end of the “Northern Regulating Structure”.

Irrigation

Yarrawonga Weir annual diverts and average of 1,900 GL per year (17% of the river’s average annual flow). Water is diverted from Lake Mulwala through the Yarrawonga Main Channel and Mulwala Canal. These two channels serve an area of over 800,000 HA, over one third of which is irrigation.

Yarrawonga Main Channel

Constructed in the mid-1930s, the Yarrawonga Main channel services the Murray Valley Irrigation Area of Victoria, which extends from Yarrawonga to Barmah, and south to the Broken and Nine Mile Creek systems. The channel has a discharge capacity of 3,100 ML/d and distributes water to an area of 128,000 HA via a network of 6 main channels and 261 spur channels.

Mulwala Canal

The Mulwala Canal is the larger of the two irrigation channels drawing water from Lake Mulwala. Construction began in March 1935. However, the whole system was not completed until 1942.

The Mulwala Canal has an offtake capacity of about 10,000 ML/d and diverts water to the Berrigan, Denimein, Deniboota and Wakool irrigation districts near Deniliquin, New South Wales – a total area of over 700,000 HA.

The Canal decreases in capacity downstream to 2,450 ML/d at the Lawson Syphons near Deniliquin, where two large concrete barrels transport water beneath the Edward River and how lying billabongs to supply the Deniboota irrigation district.

Water is also discharged into the Edward River to provide sufficient flow for diversion to the Wakool district via Stevens’s weir. The total annual water allocation to the districts exceeds 1,000,000 ML.

Hydro-Electrical Facilities

The Hydro-electric generation facility was a venture undertaken between the Rural Water Corporation of Victoria and Power Facilities Pty Ltd. Electricity generated by the station is sold under contract to Powercor Australia Ltd. Electricity generated by the station is sold under contract to powercor Australia Ltd. The ownership of the station changed hands in 2001, it is now owned by Meridian Energy a New Zealand, semi Government Corporation.

The station is un-manned and is operated from mount Beauty in Victoria by Southern Hydro, with intricate net-work links to the power station and the Goulburn Murray Water weir office.

 Construction commenced in December 1992 and power was first generated in June 1994. The stations maximum capacity is around 9 MW and operators with a maximum head differential of 9 meters and flow of up to 12,500 ML per day. 

As part of the project, a new Yarrawonga Main Channel regulating structure was required. The new structure is located 40 meters downstream of the original regulator and incorporates three 6.7 meters wide radial gates giving a total discharge capacity of 3,100 ML/d. Construction of the station and the new Channel off-take took place in the non-irrigation period of May to August 1993 and required draining of Lake Mulwala.

Fishway

A unique feature at Yarrawonga weir is a fish lift, located adjacent to the power station. Constructed in 1994, the fish lift provided the first opportunity in 60 years for fish to travel upstream. Fish are attracted to the power station discharge and into the adjacent fish lift structure. The mechanically operated lift raises fish from the river to the lake level. The cycle of fish attraction, entrapment, raising and release for the lift is automated with a PLC controlled system.

Remedial Works

In 2002, The Murray Darling Basin Commission and Goulburn- Murray Water undertook remedial works to bring this important weir up to modern day dam safety standards. The cost of these works was about $13 million. The main components of these works involved strengthening the foundation of the earth embankment, floodgate piers and the upstream and downstream wing walls of the gate structures. These works to strengthen the foundation of the embankment required stone columns to be installed. “Stone columns’ involve a pattern of compacted gravel columns immediately upstream and downstream of the embankment constructed by compacting gravel into the deep foundation.

The remedial works for the concrete sidewalls consists of strengthening works to the existing walls and installation of reinforcing cables and concrete supports.

The flood gate piers were strengthened by adding steel reinforcement and mass concrete.

The lake was drained during the non-irrigation period to allow critical components of these works to be completed.

Facts and Figures

General Information

Total Structure Length

343 m

Distance from source

538 km

Distance from Murray Mouth

1,992 km


Lake Mulwala

Full Supply Level

124,90 AHD

Area at Full Supply Level

4,400 HA

Volume at Full Supply Level

117,500 ML


Embankment

Length

271 m

Height

7 m

Crest Width

8 m


Irrigation Channels

Yarrawonga Main Channel

Discharge Capacity

3,00 ML/d

Area Served by Channel

128,000 HA

Length in Channels in System

960 km


Mulwala Canal

Discharge Capacity

10,000 ML/d

Area Served Channel

700,000 ha

Length in Channels in System

2,900 km

 

Information brought to you by Goulburn Murray Water                                                        

Address: 255 Ferguson Road, Tatura, Victoria 3616

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