shores of the lake was expanded, and sculptures and monuments were built. The completion of the central basin placed a waterway between Parliament House and the War Memorial and a landscaped boulevard was built along the land axis. A new National Library was constructed within the Parliamentary Triangle, followed by the High Court of Australia, the National Gallery and finally a new Parliament House in 1988. In 2001, the National Museum was built on the former lakeside site of the Royal Canberra Hospital. On average, the population of Canberra increased by more than 50% every five years between 1955 and 1975 as the development of the capital became more concerted. To accommodate the influx of residents, the NCDC oversaw the release of new residential land though the creation of new town centres: Woden opened in 1964, followed by Belconnen in 1966, Weston Creek in 1969 and Tuggeranong in 1973. The NCDC was disbanded in 1988, its planning authority transferred to the newly created ACT government and the new National Capital Authority, which was established to oversee Commonwealth interests in development of the national capital. Canberra has continued to grow with the further release of residential land in Gungahlin in the 1990s. 20th century development outside of Canberra A significant priority for the establishment of Canberra was the construction of water storage facilities. Cotter Dam was the first dam built on the Cotter River; construction on this concrete gravity dam started in 1912 and finished in 1915. Its height was raised to in 1951. Chlorination of Canberra's water began at Cotter Dam in 1955; operations were moved to the Mount Stromlo Water Treatment Plant in . Two additional dams were built on the Cotter: the Bendora Dam, a double-curvature, concrete-arch structure, was completed in 1961; and the Corin Dam, an earth and rock-fill embankment dam, was built in 1968. In 1979 Googong Dam was built on the Queanbeyan River in New South Wales. Transport into and out of the ACT was an early development priority. In 1931 the Federal Highway linking the ACT to Goulburn was completed, and in 1936 an airfield was constructed at Duntroon. On 1940 Australia's chief military officer and three senior ministers in the Menzies Government, James Fairbairn, Geoffrey Street and Henry Somer Gullett, were killed when their plane crashed on the southern approach to Canberra. A branch from the Bombala railway line was built from Queanbeyan