The St Clair Sea-wall
The calm, settled weather of Dunedin's autumn has made Maurice Davis grind his teeth. Each passing day brings southerly storms closer, and with them the likelihood that reconstruction of the St Clair sea-wall will begin smack in the middle of the annual tempest. Jo Register backgrounds the massive $5 million project.
Architects impression of the final seawall and Esplanade redevelopment looking south toward St Clair Hot Salt Water Pool. (click to enlarge)
As Managing Director of Duffill Watts Davis Ltd, and Dunedin City Council's engineering consultant for the St Clair sea-wall construction project, Maurice Davis FIPENZ has been frustrated by a five-month delay in obtaining the necessary resource consents. "We could have been working during this good weather. It would have been great." They were five more months tacked onto years of increasingly urgent need to upgrade the dilapidated wall. The first sea-wall – "Smith's wall" – was built in 1866; the present one was constructed in part in 1912/13, and extended between 1933 and 1938. There have been several inundations, as the different structures for taming the tide have crumbled, allowing seawater to flood several blocks inland into what is now a densely built residential area.
COP Outcome development and evaluation
Significant deterioration was apparent by the 1980s, and reports commissioned by the Council in 1985, 1995 and 1999 all recommended remedial works, ranging from significant repair to complete replacement to prevent flooding, and improve coastal protection and public access to the beach. Meanwhile, fill behind the wall washed away causing the St Clair Esplanade road to slump visibly several times, stairs leading down to the beach collapsed completely, and the beach and adjoining dune were being scoured away by wave energy reflected off the old flat barrier. At the southern end of the beach, the sea-wall surrounding the recently renovated St Clair Hot Salt Water Pool was also providing less and less adequate protection from the sea.
"When the wall was first built there wasn't a lot of knowledge about good sea-wall practice," says Mr Davis. Remedial work has been carried out after each problem has emerged, but without the benefit of the technology and understanding that are now available.
This case study is reproduced with permission from e.nz magazine. Subscriptions to e.nz are discounted for schools and TENZ members.
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