The Harvey River Diversion Drain

The Harvey River Diversion Drain takes water from the Harvey River catchment into the Indian Ocean south of Myalup

The Harvey River Diversion Drain (HRDD) was built between October 1931 and December 1932 as a way to reduce flooding across the Harvey agricultural region. Construction was undertaken to mitigate flooding of agricultural land following large scale clearing of vegetation in the district and the recent success of the Peel Main Drain and the Serpentine Diversion Drain made a new drain a viable solution.

At 25km in length on completion, the drain (on average 10m wide at the top and between 6-8m deep) was constructed largely by hand by a 2,500 strong workforce, mainly using shovels and wheelbarrows. An impressive feat indeed for the time.

Now augmented by myriad smaller local drains criss-crossing the landscape, the HRDD and other drains still function today and plays a key role in flood abatement for farmers and towns in the region. But there are some challenges with these drains too.

Fertilisers and other chemicals are concentrated and carried in the water, erosion along the drains transports sediment that can cause blockages reducing the drains’ effectiveness and often the vegetation along drains has low natural values. These drains also require regular maintenance to ensure they work properly to convey water, whether they are large or small, requiring continual investment of time, knowledge and money.

Wetland ecosystems and the species that depend on them require periods of inundation over winter to recharge groundwater levels, which can be impacted by poor drain management. Some remaining wetlands on farms and in reserves have been impacted by the historic changes in water level, while other new wetlands have grown in response to the modified hydrology.

In 2005 the outflow of the HRDD into the Indian Ocean was estimated at 26,000,000,000L. To put this into perspective, that is about one quarter of a million standard-sized backyard swimming pools!

And one of the most surprising things about the HRDD is that this water flows out into the ocean, rather than feeding the multitude of small and large wetlands in the area it drains.

So next time you cross the Harvey River Diversion Drain as you travel around or through the Harvey Region, spare a thought for the role it and other drains have for agricultural production, the impact drains have on our natural wetlands and the volume of water moving from farms and towns in the district into the Indian Ocean.