Erosion at beach outfall

Press, 20 July 1977, Page 6

Erosion at beach outfall

Some Christchurch Drain-1 age Board members are wor-; tied about the possible damage arising from beach eros-!; ion at a sea outfall from the I future northern treatment! works. “The amount of beach ero- ■ Sion at the moment is as, dramatic is I have ever seen,' it,” said Mr C. H. Russell. He said that a large proportion of a feasibility study on i the proposed ocean outfall, would have to be referred to I board engineers and back to! consultants before any final 1 action. The report said that out-1 fall construction south of j; Spencer Park was feasible,,, and no exceptional problems!, in design and construction, were foreseen. For a 1700 m outfall, the! estimated cost is 53.9 M; for a 4000 m outfall, the cost is! put at 56.6 M. According to Morris and

iWilson, consulting engineers, ja buried pipeline would be (necessary through the beach land surf zone for environ- • mental and structural reaisons. The surf zone extends ifor about 500 m, and a pipeline exposed to severe sea bed changes in that distance would not remain sound for : long. Beyond the 500 m mark, the consultants considered the sea bottom stable enough for the (pipeline to be in the open. ‘ The report itself said that further studies should be made before a final design (was made, Mr H. W. Thompson said that he was conicerned about beach-scouring effects during nor’westers. (Deep potholes and trenches 'were common. ( Mr R. S. Leach said that lit was “a complete fallacy” (to conclude the sea bottom I was stable because of the ! beach’s nature.