The Bremer River wooden irrigation diversion weirs are a series of levee banks and small wooden floodgates used to divert the floodwaters of the Bremer River into vineyards before discharging the water into adjacent Ramsar listed Wetlands of international importance. Built in the 1890s on the Bleasdale property near Langhorne Creek in South Australia, the first of these diversion weirs (c. 15 feet wide by 12 feet deep) was constructed of four massive sawn Redgum logs embedded in masonry piers in the banks of the Bremer River secured to a concrete platform.

Diverting the water of the Bremer River was essential for the European settlers to obtain productive food crops and to stimulate the burgeoning economy of the region because of its semi-arid nature and unreliable rainfall (390 mm average annual rainfall of which only 110 mm is received in the November – March period).

Description

The floodgates are simple and strong precisely shaped Redgum planks that are dropped into grooves in the stone piers. Individual logs can be removed or replaced to control the level and thus the volume of water entering the vineyard. They bear testament to the capacity of the settlers to utilize existing resources in a sustainable manner upon which has been built one of South-Eastern Australia’s premier viticulture regions. Vineyard managers still use these structures to divert floodwaters for passive irrigation today and to prevent saline groundwater upwelling into the irrigation area as the floods move through the district.

There is no formal management of the diversion process, which relies on communication between adjoining landholders to enable water to flow between irrigated blocks. Generational ownership of the properties has ensured continuity of these traditional practices. Legislation in South Australia has acknowledged the outstanding contribution of these diversion weirs to modern productivity in an environmentally sustainable manner. Diversion weirs and levee banks have been mapped and licensed for contemporary use under the Water Allocation Plan for the Eastern Mt Lofty Ranges.

Along with irrigation water, the diversion of floodwaters ensures that the aquifers are recharged and the adjacent iconic Redgum swamps and Lake Alexandrina receive environmental water.

The Bleasdale Vineyards flood gate is still operational today which is a testament to the simple yet effective design and operation of the structure. Over the years there have been incidences where the quality of received floodwaters has been impacted by upstream activities including mining and urbanisation.

Water Heritage

The floodplains of the Angas and Bremer Rivers are part of the traditional homelands of the Ngarrindjeri people who flourished on the abundant native foods of the area for many thousands of years prior to European settlement. South Australia is the driest state in the driest inhabited continent on Earth. The semi-arid nature of the agricultural land and the lack of reliable rainfall has made sustainable irrigation a challenging enterprise since European settlement (1836). Mr. JD Cave a new settler in reported various dryland agricultural pursuits were attempted around Langhorne Creek but it was described as ‘large tracts of the country bearing small crops owing to lack of moisture’ although ‘an immense body of water was yearly running away’ in 1859 at an irrigation meeting.

Early structures focused on the standard practice of damming the Bremer River and its neighbouring Angas River to enable irrigation and better utilisation of the land. The local residents concluded that dams were inappropriate infrastructure because of the need to keep the rivers running in their original courses across the relatively flat landscape, which was innovative thinking that retained the iconic Redgum swamps as natural resources for timber and helped the control of groundwater rise across the region.

Wooden diversion gates on the rivers and between properties were seen as fit-for-purpose, allowing everyone to share the water resource and collect the silt from the river to fill depressions and create suitable topography for establishing irrigated crops, including grapevines for wine and dried fruit. The use of diversion weirs as opposed to dams also enabled irrigators to selectively harvest water of the best quality, letting any pollution released from the new townships in the Adelaide hills to bypass the vineyards.

The first diversion channel was built on the Bleasdale property in the 1860s to drain water from the Bremer River to a depression, which was both irrigated and filled with silt to create flat land. The floodwaters were relatively uncontrolled through this channel and the debris carried with the water caused substantial infrastructure damage, resulting in the construction of the first wooden diversion weir that could be operated to regulate flow and control inputs.

Successful installation and operation of many of these diversion weirs embedded in levee banks over the next few decades was the foundation of viticulture in the region and facilitated the formation of the Langhorne Creek Grape Vendors’ Association in 1929. Certainty of fruit supply enabled wineries to also develop and in ‘bad’ years, currant grapes that were grown for drying could be sold for distillation at Bleasdale winery thus providing secure income for the rural community.

The construction of such simple yet sound irrigation infrastructure in the form of these wooden diversion weirs has sustained the environmental assets of the region that would have been destroyed otherwise. Water that has been used for irrigation or is diverted away from crops, drains into the Redgum swamps in the region and into Lake Alexandrina, which are part of the Ramsar-listed Coorong and Lakes Alexandrina and Albert Wetland of international importance.

During the Millennium Drought (2000-2010), the majority of the Redgums along the lower River Murray that also feeds into Lake Alexandrina were in poor health (75% in Health Class 1 or 2) due to the legacy of building large storages and over extraction of water across the Murray-Darling Basin. By stark contrast, more than 80% of the Redgums in the Angas Bremer Irrigation Management Zone were in the top two health classes (Class 4 or 5), having been sustained by regular and appropriate flooding.

The redgums would likely have been lost, or substantially degraded if the initial plans for damming the Angas and Bremer Rivers had been implemented in the 1800s. The development instead of a series of diversion weirs is a testament to the irrigation excellence and positive outcomes of using simple technology at Langhorne Creek for sustaining irrigation and environmental assets for more than 100 years.

The recently published (2015/16) Irrigation Annual Report of the Angas Bremer Water Management Committee reported that the district had 7,011 ha of irrigated crops of which 5,658 ha were wine grapes. The average district water use across all crop types was 2.99 ML/ha and 2.88 ML/ha for wine grapes.