8 Jan 2021

The unsung hero of Sydney’s west

For most of us, the modern world provides the convenience of a never-ending supply of clean and safe drinking water whenever we turn on a tap.

However, at the Australian Botanic Garden Mount Annan, the main water supply is principally derived from a very special water canal built in the 1880s, which is on the State Heritage Register.

Sydney water supply — Sydney Water Supply poster circa 8 May 1895. From the collections of the State Library of New South Wales.

The water source

WaterNSW's Upper Canal is a remarkable engineering feat, delivering water from four water supply dams to the south of the Garden (Cataract, Cordeaux, Nepean and Avon) to Prospect Reservoir in Sydney's west.

Currently, 20 per cent of Sydney’s drinking water travels through the Garden on a 64 km journey, dropping a mere 50 m elevation in all but 10 km of the canal’s length.

At times it can supply up to 40 per cent of Sydney's daily demand – an extraordinary feat considering it uses no energy other than the earth's gravity to transport water.

/Sydney-Water-Supply-Prospect-Hill-c1890.jpg.aspx — Sydney Water Supply construction at Prospect Hill circa 1890.

Heritage significance

spillway and canal 1888 Holroyd City Council.jpg — Spillway and canal at Prospect Hill circa 1888

When the canal was was constructed more than 1,000 men were employed on the project and the entire length of the canal was dotted with tented construction camps. It is thought that the sandstone blocks were quarried from Mount Annan using horses - the only mode of transport at that time.

The canal is built from a variety of materials, depending on which stretch of land the water is passing through. Where the ground is soft, the canal is lined with unreinforced concrete slabs. In other sections, sandstone masonry is used, or the canal is cut directly into solid rock.

Interact sandstone and solid rock tunnels allow the canal to pass under the hills of Sydney. Aqueducts allow the canal to cross creeks and gullies – one of which is located in the Garden.

In all, the Upper Canal has one kilometre of aqueducts crossing nine creeks and the Southern railway line, nineteen kilometres of tunnels and 44 kilometres of open canal.

canal hero — Construction of the Upper Canal in Mount Annan.

Did you know? Torpedo nets were placed at Cataract and Cordeaux dams at the beginning of WWII to protect Sydney’s water supply from being destroyed by enemy attack and a small garrison was positioned in the Garden next to the canal to protect it.

Upper Canal 19th century.jpg — The Upper Canal completed in Mount Annan circa 1900.

The Upper Canal

Many of the original iron pipes and mechanisms to control and divert the water's flow - such as stop logs, penstocks, and gate valves - are still in use.

The Garden has sections of sandstone-lined open canal, as well as a beautiful brick-constructed arched aqueduct hidden among an African olive forest, and a tunnel section under the eastern ridge line.

Eastern ridge water canal stone cairn — Original stone cairn in the Garden near the Eastern ridge.

Winding its way through the Garden

The Garden’s irrigation infrastructure draws water from the canal opposite the Australian PlantBank and pumps it uphill some distance to the tank behind the Connections Garden, where it is pressurised and distributed around the Garden.

Our horticulturists endeavour to minimise water consumption, the use of native plants across the Garden make a significant difference to our water usage and security.

To learn more about the heritage and cultural significance of the Garden visit our history page here.