Cattai Creek bridge should have been built three metres higher, says Glenorie resident Peter Roach.
"The bridge the other day went under [water] by a metre and a half to two metres and the water lay there for three to five days," Mr Roach said.
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He is "baffled" why The Hills Council replaced the wooden bridge with a bridge less than a metre higher.
"I've been living here for 30 years and the whole thing is a disaster," Mr Roach said.
The bridge was replaced in 2008 by the council — part of a state government scheme to replace ageing timber bridges on regional roads.
The RTA provided $475,000, which the council matched, and funded an investigation into design options, including larger bridges.
A council spokeswoman said raising the bridge height and improving road links would cost $11 million.
"This bridge was chosen because it minimises the hydraulic impact on the creek system while maximising improvements to the level of service . . . from flooding about five times a year, to about one to two times," she said.
Hills SES local controller Evelyn Lester said: "It's usually our last road to go under.
"Blue Gum Road in Kenthurst and McClymonts Road at Maraylya go first."
The council will replace two timber bridges on Pitt Town Road, near the boundary of Kenthurst and Maraylya.