Expedition Pass Reservoir - A Happy Accident

 

Expedition Pass Reservoir, ca. 1915

Residents of the Castlemaine region are very fond of  the Expedition Pass Reservoir or 'The Res', as they call it. Drop past on a warm summer's day and cars will be parked everywhere without a thought for safety or risk of parking fines. The swimmers there might be familiar with its history as the original main Castlemaine water storage but not many will know why it lost that function, much less for the reason for me viewing 'The Res' today as a 'happy accident'.

    It all started back in the early 1860's. A reliable source of water was sought for the Bendigo Castlemaine region. Joseph Brady came up with a scheme to impound water at Malmsbury and for that water then to be run along an open channel to storage reservoirs at Big Hill and Golden Point. His scheme was given the go ahead in 1865 and the construction of the reservoir at Malmsbury begun in 1866. The story is told in much greater detail in my book 'The Coliban Main Channel: A Walking Guide' (2023).

    Before this, Castlemaine and Chewton had been serviced by small reservoirs such as Commissioner's Gully Reservoir at Golden Point and Dinah's Flat Reservoir in Chewton. It was hoped that the new larger reservoir at Expedition Pass would provide a more assured supply. From the start, the Pass, made famous for having been traversed by Major Mitchell's expedition, must have appeared a likely location for a reservoir. It's a narrow ravine that funnels water from the slopes of Mount Alexander via Forest Creek to Campbells Creek and then on to the Loddon River near Guildford. So it was surmised that a reservoir here might have a sufficient catchment to augment the supply from the Coliban channel. Construction began in early 1867 and completed by late 1868. 

    However, problems with the siting of the reservoir soon became apparent, rapid siltation for one. It was discovered that by 1872 the capacity of the reservoir had shrunk from 120 million gallons to 100 million gallons. It was predicted that it would be 'obliterated' within 80 years (Metcalfe Heritage Study). 

The blue line marks the pre-existing watercourse used to transport Coliban water to the Expedition Pass Reservoir (1945 aerial map).

Porters Tunnel outlet, ca. 1890

    So, what was the reason for this siltation? The construction of Porters Tunnel, Faraday, around 395 m in length, had been crucial to the scheme. The tunnel had allowed the Coliban water to pass from the drainage basin of the Coliban/Campaspe River to enter that of the Loddon River. The hill above the tunnel might be barely discernable but it's enough to divide the two major catchments, part of a low ridge or saddle which links the Chewton Bushlands range of hills to Mount Alexander. 

    Porters Tunnel was completed early, about the same time as the Expedition Pass Reservoir. However delays in the Coliban Scheme meant that the tunnel sat unused for 6 years. During that time various rain events caused water to build up in this section of the channel. Around 1870 it was decided to release the water through the tunnel. The result was disastrous. There is a drop of over 40m between the outlet of the tunnel and Forest Creek. This allied with the soft nature of the creek banks meant a great load of sand and clay was washed down, scouring the gully, and the accumulated debris deposited in the upper section of the reservoir. This gully leading to Forest Creek was really too steep to be used as an aqueduct. Eventually 24 weirs and waterfalls were constructed in this watercourse to dissipate the energy of the cascading water but by that time the damage had been done.

    In the map below, the low ridge (an area above 1400m) connecting the hills west of Harmony Way with Mount Alexander can be seen (from bottom left to top right). At the time it might have appeared to Joseph Brady, the architect of the Coliban Scheme, to be a stroke of luck that the watershed could be breached so easily but the full price was yet to be paid!    

    

    There were some additional problems with Expedition Pass reservoir. A road linking Golden Point and Faraday passes above the reservoir. Early on it was remarked that this would mean that dung, dust and other refuse would be washed into the reservoir. In those days the water flowing into Castlemaine and Chewton along pipes laid along the roadside was untreated. This became an even greater issue when a school at Faraday was built on higher ground to the near east. The school, being unsewered meant that children in need of the toilet simply dug a hole nearby. When the link between various diseases and polluted water became too strong to ignore, the clamour of discontent grew louder. 

    This and the desire to increase the water pressure in the higher parts of Castlemaine meant that by the end of the century, a new reservoir was called for. It took until 1913 for the Golden Point Reservoir to be constructed in the hills high above the Expedition Pass reservoir. It solved these problems but introduced some others. In its isolated location, no roads or human habitation threatened its water quality and its extra height above sea level solved the water pressure problems of Chewton and Castlemaine. On the debit side the new reservoir was much smaller than Expedition Pass Reservoir, with a negligible catchment; it relied almost exclusively on the inflow provided by the new Golden Point Reservoir race for its supply (see map above).
    An alternative might have been staring everyone in the face. In 1875, the year after water first arrived from the Coliban Channel to the Expedition Pass Reservoir, it was decided to drive a second tunnel through the Range separating the two major drainage basins. This was Coopers Tunnel, at 650 m, longer than Porters Tunnel but more modest in dimensions. The water diverted through this tunnel was originally earmarked for miners and would be distributed along a host of minor races to various diggings. The feeder race these days is generally known as the Poverty Gully Race and was decommissioned only relatively recently. Part of it is still in use, the section leading to the current main Castlemaine water supply, McCay Reservoir, built in 1960 when the the region outgrew the small Coliban storage reservoirs.

Coopers Tunnel outlet

    Here's the interesting point. Why didn't Joseph Brady plan a large reservoir roughly where McCay reservoir is today? Such a reservoir would have been isolated, far from human habitation and other sources of pollution. In addition, it would have been at a higher altitude than Expedition Pass Reservoir, so would have provided more water pressure in Castlemaine and Chewton from the outset. There would have been no problem with siltation and the pipeline to Chewton and Castlemaine would have been shorter in length. A considerable amount of money would have been saved.

    Certainly McCay Reservoir has a very limited catchment but certainly no less than the Golden Point Reservoir. But given the locals' love affair with the Expedition Pass Reservoir, now a major recreational lake, they would probably agree it was indeed a happy accident.        

McCay Reservoir ca. 1960s (looking south-east)