the 1970s, the Engineering and Water Supply Department chose an area at the top of the park, adjacent to Lower North East Road, to build a water treatment works. Based partly on seismic refraction traverses, a ridge underlain by dolomite and quartzite was deemed to be stable enough for construction. The site was also selected because of its hydraulic advantages; all other sites would have required the construction of a major pumping station. The exact placement of the site was made so that it could not be seen from the metropolitan area. It has a design flow of 313 megalitres (ML) per day with a maximum capacity of 344 ML. The plant was commissioned in 1980 and uses filtration and sedimentation techniques to clean water from the Mannum to Adelaide pipeline. It was the second plant in Adelaide, after the opening of the Hope Valley plant in 1977. Most of the water is piped directly from the River Murray, but some is sourced from Millbrook Reservoir. The plant was intended to serve 70,000 homes in the outer northeastern suburbs of Adelaide, specifically those north of the River Torrens. The total construction cost was $14.5 million, including changes to the existing pipeline. As of 2005, the plant filters approximately 20% of Adelaide's water supply. A small hydroelectric plant began operating in adjacent Hope Valley in 2003, using the head of water as it flows down Anstey Hill. The plant is designed to supply 7,000 megawatt hours per year. Roads Lower North East Road runs around Anstey Hill and up the escarpment of the Burnside-Eden Fault Zone. It connects the suburbs—formerly villages—of Hope Valley and Houghton. Three roads were surveyed and built to connect the same locations. The first was a private road constructed by George Anstey in 1841—although officially surveyed in 1844—to reach his estate, as a mostly straight-line extension of Grand Junction Road. It followed the base of a gully, before rising steeply up Anstey Hill. From 1842 to 1846, Anstey constructed a replacement private road with a devil's elbow (double hairpin bend) that followed the land's contours more closely. As Chairman of Roads for the District of Yatala, Anstey allocated most of the district's funding to his road, leading to a public outcry that forced him from office in 1851. This ungravelled road became known as Anstey Hill Road and remained in use for 20 years. New Road, later