Halswell River damage minor

Additional restoration work required to the Halswell River as a result of the 22 February 2011 earthquake is estimated to cost $60,000.

Environment Canterbury’s Principal River Engineer Ian Heslop says that the February earthquake caused some deterioration of the Halswell river and drainage network.

“There was some liquefaction and blockage of the drainage network, this was generally in the same areas but to a lesser extent than the September earthquake,” he says.

The 22 February earthquake caused some existing river bank cracking and slumping deterioration in a few areas but there were no instances of significant new slumping and river bed liquefaction appears to be substantially less.

Damage from the September earthquake consisted of blockage to the contributing drainage network due to liquefaction and this caused a significant reduction in drainage flow capacity.

“The September earthquake recovery consisted of an initial $570,000 programme of drain cleaning, river channel dredging and tree clearance, and removal of major slumps,” he says.

The goal was to restore normal drainage and river flows capacity as much as possible in the short term and the initial programme of work has been largely completed.

“In addition a three year programme of works has been approved by the local community and consists of further river channel dredging and widening, tree removal, removal of slump and slop stabilisation over a 20km length of river,

This has an estimated cost of $3 million starting next financial year and is hoped to fully restore the pre-earthquake drainage system flow capacity and bank stability or the Halswell River,” says Mr Heslop.

It is hoped that the additional repairs from the February earthquake can be incorporated into the initial and ongoing three year $3 million restoration programme.