| Physical description: | STRUCTURES
bridge across Clarence River - double deck road/rail bridge with Bascule span, 1932, RNE
timber viaduct south of station, 1915
As early as 1910 the Chief Commissioner of the New South Wales Railways wrote to the Public Works Department pointing out the necessity of a bridge over the Clarence River at Grafton and, although plans were prepared for a tentative six-span design by the Public Works Department, they were shelved with the outbreak of the First World War, so train ferries and vehicular punts continued to be used. Various sites had been looked at for the bridge, including Susan Island, Mountain View, and the present location, known as Wilsons Hill. Before actual working drawings were commenced a complete reinvestigation was made of the most efficient form of pier and method of sinking, etc. A solid pier in one unit was finally decided on for piers Nos 2,3 & 4 to be sunk to rock by means of rectangular steel caissons, and for the pier in the southern bank of clay an open excavation was chosen. Five spans were decided on and the bascule span was the Scherzer rolling type, a swing span and vertical lift span having been earlier ruled out. The amended design of the railway bridge was approved & working drawings were begun by the Railway & Tramway Department early in 1921. However, when the drawings were well advanced in December, 1922, the Minister for Works asked the Railways Commissioners to prepare new designs and estimates for a bridge to carry vehicular traffic as well. Alternative schemes were considered but putting a roadway above the railway was found to be not only the cheapest arrangement but also allowed all the previous calculations to be used. The original departmental estimate for the bridge was 400,000 pounds and when tenders were called in June, 1927, with a stipulation that only Australian steel be used throughout, only two were received, one for 488,000 pounds and the other for 497,000 pounds, so the department decided to do the work itself and in the event did it for less than its own estimate -- a far cry from modern construction estimates. Preliminary work was started in August and in the same year tenders were accepted from the Clyde Engineering Company Ltd for the manufacture and supply of steelwork for the caissons (22,000 pounds) and for the superstructure (144,500 pounds). In June, 1928, the first big pontoon for use in the work was launched at Grafton and in July the first rivet was driven by Minister for Works and Railways. In October the excavations for the first pier on the southern bank of the river were completed and filling with concrete began. Building the remaining piers proved to be the most arduous and difficult part of the undertaking but in May, 1930, the first span was floated into position and the last span early in 1932. All the bridge members were built at Granville, sent up by train, then assembled on site. The most fascinating feature of the bridge is the bascule, which was electrically operated by two 35 horsepower (26kW) motors powered by the Nymboida hydro-electric scheme. The span is of the Rall (combined rotating and travelling) type, weighs 800 tons and is carried on two large steel rollers each about 5 ft (1.5m) in diameter and 2 ft (0.6m) in width, which rolled on a steel track. The rollers moved away from the opening simultaneously with the upward rotation of the span, so that with the maximum angular movement of 80 degrees the rollers had moved back 12 ft 6 ins (3.8m) from their original position. This left an opening of 70 ft (21.3m) and with 40 ft (12.2m) of water in the channel vessels of up to 2,500 tons could pass through. The whole lifting operation took 2 minutes and occurred 4-5 times a week. As finally built the bridge consists of five steel truss spans of from 212 ft 6 ins (74m) to 245 ft (75m) in length, with the bascule span of 76 ft (23.2m) and two approach spans, being 66 ft (20m) long for the railway and 100 ft (30.5m) long for the roadway. The total length of the bridge is 1,500 ft (457m) and it spans 1,300 (396m) of water. CONSTRUCTION OF THE DAM (continued) During construction of the dam extensive use was made of electricity on site, and production line techniques for the quarrying of stone blocks were used for the first time. SUMMARY OF THE SPECIFICATIONS OF THE DAM Date of construction: 1902 - 1907 Masonry in wall and spillway: 148,000 cu. yds (113,220 cu. m) Length of dam: 811 ft (247.2m) Length of bywash: 684.5 ft (208.6m) Width at base: 156 ft (47.6m) Width at crest: 16.5 ft (5m) Greatest depth of water: 150 ft (45.7m) Full supply level: 950 ft above sea level (289.5m) Area of lake: 2,104 acres (851.5 ha) Capacity: 20,743 million gallons (94,298 million litres) The water from Cataract Dam is discharged as required into the Cataract River downstream to Broughton's Pass. There it is diverted by another weir into Cataract Tunnel, 2 miles 93.2 km) long, the first structure of the Upper Canal by which it is conveyed to Prospect Reservoir. Also to be included in this classification is the CATARACT DAM OFFICIAL QUARTERS, situated close to the dam wall at the northern end. This single storey Federation house was built in 1910 for the use of Water Board staff during construction of the dam. It is built of ashlar masonry quarried on the site and features a verandah at the front with white painted timber posts with curved brackets and gabled entrance way. When built the house contained a board room, offices, four bedrooms and a kitchen. Over the years it provided accommodation for inspecting officers and important visitors. Today it is still used by the Water Board and can now provide sleeping accommodation for 12 people. The gardens around the house are landscaped and the garden beds edged with sandstone. Also made of sandstone is a detached garage and two amenity blocks. Surrounding the garden is a castellated sandstone fence with decorative entrance posts. A further three sandstone cottages are located nearly as well as a brick cottage. The Cataract Dam site is a very popular tourist attraction. The public area surrounding the dam is beautifully maintained by the Water Board and a large picnic area, shelter sheds, fireplaces and playground area are provided. There are also attractive gardens and bushwalks. BOUNDARY AND CURTILAGE Classification to include Dam Wall, Official Quarters and grounds defined by line from dam wall trig (9029-II-N GR 975060) to road junction at entrance to picnic area (GR 981066) around vehicle track to landing area (GR983060) and line projected back to dam wall trig. Architectural Style: Scherzer rolling type bascule span bridge. Building Material: Steel
A 6-truss steel bridge linking South Grafton to Grafton. It has the distinction of being a double-deck bridge, the road being on top of the trusses, and having a double-deck bascule span for ships to pass through.
Its design was the crowning achievement of the distinguished bridge engineer J W Roberts.
Drawings in PH 1711 (3 rolls). |