Work is under way in Christchurch to restore stopbanks damaged in the earthquake ahead of higher than usual tides.
Mayor Bob Parker says the spring tide forecast for this weekend will result in a tidal level of 10.3 metres, 20 cm higher than a normal high tide.
Mr Parker says some of the stopbanks have collapsed inwards into streams.
He says they will be repaired and increased to about 10.9 metres as a precautionary measure.
Mr Parker says they are focussing on low-lying areas such as Bexley, New Brighton, Avondale and Horseshoe Lake.
He says in the four areas where heavy machinery can't get access, volunteers are sandbagging the rivers.