 At the time it was intended to deliver water from the Upper Nepean Scheme via the Upper Canal to the reservoir.The quintessential feature of the scheme was the diversion of the Nepean River below its junction with the Avon and Cordeaux Rivers.The Pheasant's Nest weir, near the township of Wilton, diverts the water through a 7 km long tunnel to the Cataract River at Broughton's Pass, near the township of Appin, where a similar weir diverts the flow of the four rivers through a 58 km system of tunnels, aqueducts and open channels to Prospect Creek upon which the earthen dam wall is located.