This week, Roy decided he really wanted to check out a bridge. Roy loves bridges. There is just something about them which grabs his attention. Whether it is a stone bridge, metal, wooden, big, small, they just fascinate him. So, he was looking for an interesting bridge to visit, which was close to home. When he found one at Bobbin Head in Kuringai Chase National Park he was stunned. He must have driven over the Cockle Creek Bridge hundreds of times, but he never knew it was particularly significant!
If you would like to visit the bridge over Cockle Creek, it is located in Bobbin Head, not far from Hornsby. To get there you can enter from Bobbin Head Road in North Turrumurra or from Kuringai Chase Road in Mount Colah (enter from the Old Pacific Highway into Yirra Road, then turn into Belmont Parade and from there into Kuringai Chase Road). While you are at the park, why not go for a bushwalk, enjoy a meal or take in the mangroves!
The bridge over Cockle Creek at Bobbin Head is very significant, though the reason why seems to be little known. Certainly, Roy and I had no idea the bridge was the first of its kind in Sydney, or that it was heritage listed by the RTA. This bridge, which while it’s a nice bridge doesn’t appear particularly exciting, was the first pre-stressed concrete bridge to be built in Sydney. So what is a pre-stressed concrete bridge and why is it important? Pre-stressed concrete is a way of making concrete which overcomes its natural weakness. Concrete which is normally reinforced, with metal bars, cannot be used to make a long spans because it’s weak over such a long distance. Pre-stressed concrete has pre-tensioned ‘tendons’ put in it, which are usually cables. The cables are pre-tensioned and then the concrete is poured over them and this gives much greater strength. Following the success of the Cockle Creek bridge this method of bridge construction became popular in Sydney.
Why go to such effort for a small bridge in an out of the way place like Bobbin Head? At the time the bridge was built, 1956, Bobbin Head was a popular pleasure ground. There was a swimming pool, play equipment, a miniature train, restaurant, boat sheds amongst other attractions and people loved to visit. Bobbin Head was named a National Park in 1894 and from this time onwards the area was popular with visitors. The problem though was that Cockle Creek ran through the pleasure ground area, so a bridge had to be built to enable people to come from both directions, and to utilise both sides of the pleasure ground. The first attempt was made in 1902 and 1903 when a causeway was built, but this was washed away in 1915. A new bridge was the built of timber but by 1925 the bridge and a wharf had been washed away. A temporary bridge was built, and then a proper one was constructed in 1930. Yet again, it was washed away in 1942. Storms were a real problem when it came to building a lasting bridge. It was important that people could pass under the bridge in boats, as this was one of the main pastimes, but the bridges just didn’t seem to be strong enough to survive the storms which hit the area. Then, in 1956, a new type of bridge was trialled, the pre-stressed concrete one. It’s still there today.