Birrega Main Drain

Birrega Main Drain
The Birrega Main Drain south of Mundijong Road, in Baldivis
Route of the Birrega Main Drain
Location	Perth, Western Australia
Country	Australia
Coordinates	32°13′50″S115°55′49″E / 32.230607°S 115.930211°E / -32.230607; 115.930211
History
Construction began	1920s
Geography
Beginning coordinates	32°11′33″S116°00′32″E / 32.192397°S 116.008782°E / -32.192397; 116.008782
Ending coordinates	32°19′57″S115°52′29″E / 32.332451°S 115.874832°E / -32.332451; 115.874832

The Birrega Main Drain is a drainage canal in the southern suburbs of Perth, Western Australia. Construction of the canal commenced in the 1920s. The canal stretches from Darling Down, where it starts just west of the South Western Highway, to Baldivis, where it discharges into the Serpentine River. A second major drain, the Oaklands Main Drain, flows into the Birrega Main Drain, dewatering an area south-east of the latter while a number of smaller rural drains in turn flow into both. The two main drains have a combined catchment area of 185 square kilometres (71 sq mi). ^{[1] [2]}

Like the Peel Main Drain, which also discharged into the Serpentine River, the Birrega Main Drain was part of the Peel Estate. ^[3]

Route

The Birrega Main Drain was constructed in the 1920s, ^[3] when the Birrega Brook was dammed back for the purpose of using its water for irrigation. ^{[4] [5]} The drain was not constructed for flood protection but rather to dewater its drainage area to make it suitable for agriculture by alleviating water logging in winter. ^{[1] [2]}

The drain begins west of the South-West Highway as a minor off-take of the Wungong Brook, downstream from the Wungong Dam. ^{[1] [2]} Only a small portion of the water of the Wungong Brook flow into the Birrega Main Drain but this can be expanded to up to 50 percent of its flow. ^[6]

It originates in Darling Down in the Shire of Serpentine-Jarrahdale before flowing north-west, passing through the south of the City of Armadale. In its early stages, the drain is only one metre deep but has expanded to a depth of two metres and a width of ten by the time it passes into the City of Armadale. The upper parts of the drain have no significant levees. ^{[1] [2]}

The drain changes from its westerly direction to a southerly in Oakford and reaches a width of 40 metres at Mundijong Road, where it enters Baldivis and the City of Rockingham. South of Orton Road, the drain has substantial levees but these are not designed for flood protection but, instead, result from spoil from drain maintenance. The Oaklands Main Drain flows into the Birrega Main Drain just north of Mundijong Road. ^{[1] [2]}

The levees in the section north of Mundijong Road have a series of breaks to allow inflow from other drains, with the possibility of large floods through them in north-east Baldivis during a major flood event in line with the ones experienced in the winters of 1945, 1964, 1987 and 1996. ^{[1] [2]}

The drain flows into the Serpentine River at Baldivis, west of the historic Lowlands Homestead. ^{[1] [2]}

Controversies

The upper reaches of the drain, in Hilbert, where scheduled to be revegetated as part of the construction of The Avenues housing estate, being advertised as the Birrega Living Stream. In 2023, six years later, local residence criticised the developers for not fulfilling this promise. The developer, blamed approval delays and market conditions for the lack of progress in the development around the water way. ^[7]

A side effect of the Birrega Main Drain connecting to the Wungong Brook is the linking of two normally separate catchments, the Swan Coastal Catchment and the Peel-Harvey Catchment, which has led to the spread of invasive species from one catchment to the other, like the pearl cichlid. When this was discovered in 2015, the Western Australian Department of Fisheries and key stakeholders moved to block the junction of the two. ^[8]

References

1. Birrega and Oaklands flood modelling and drainage study (PDF) (Report). Government of Western Australia - Department of Water and Environmental Regulation. 3 August 2015. Retrieved 2 December 2024.
2. East of Kwinana flood modelling and drainage study (PDF) (Report). Government of Western Australia - Department of Water and Environmental Regulation. September 2021. Retrieved 2 December 2024.
3. "File 13004 - Peel Estate Drainage. Birrega Main Drain Traverse. Field Book. 09/05/1924". State Records Office of Western Australia . Public Works Department of Western Australia. 9 May 1924. Retrieved 2 December 2024.
4. "Peel Estate Commission". The Daily News . Perth: National Library of Australia. 9 February 1924. p. 9. Retrieved 2 December 2024.
5. "Metropolitan Water Supply". The Daily News . Perth: National Library of Australia. 12 February 1924. p. 1. Retrieved 2 December 2024.
6. Wungong Urban Water Redevelopment Scheme 2006 (PDF) (Report). Environmental Protection Authority of Western Australia. 4 April 2007. Retrieved 2 December 2024.
7. Brookes, Sarah; Hastie, Hamish (8 November 2023). "The good, the bad and the ugly: What's it like living on Perth's urban fringe?". WAtoday . Retrieved 2 December 2024.
8. What is aquatic biosecurity and why is it important? (PDF) (Report). Government of Western Australia - Department of Fisheries. January 2015. Retrieved 2 December 2024.

External links

• Serpentine River - Birriga Drain (Department of Water and Environmental Regulation)