The science of ‘aquitards’

The Press - - Front Page - Colin Wil­lis­croft

Can­ter­bury’s aquifers may have made Christchurch the worst place in the world for earth­quake liq­ue­fac­tion.

Flooded fields have some wor­ried the site of the new Red­cliffs School was a bad choice but the Ed­u­ca­tion Min­istry says re­cent rain is not re­spon­si­ble.

Much of Red­cliffs Park was un­der wa­ter this week, ap­pear­ing to sup­port con­cerns from neigh­bour­ing res­i­dents about reg­u­lar flood­ing at the re­serve and sur­round­ing streets and roads.

The min­istry said the park’s flooded state was not be­cause of re­cent rain, but was caused by work hap­pen­ing on the site.

Min­istry ed­u­ca­tion in­fra­struc­ture ser­vice head Kim Shan­non said a waste­water main was be­ing in­stalled be­fore work to build the school be­gan next year.

Part of the work in­volved ‘‘de­wa­ter­ing’’ – or low­er­ing the ground­wa­ter ta­ble – by pump­ing ground­wa­ter into a sed­i­ment tank, then dis­charg­ing it to nearby play­ing fields, she said. That al­lowed the waste­water main to be in­stalled. Once that was done, de-wa­ter­ing equip­ment would be re­moved and the ground­wa­ter would re­turn to its usual level.

Shan­non said the work was ap­proved by En­vi­ron­ment Can­ter­bury (ECan) and was ex­pected to be com­pleted by De­cem­ber 14. Fur­ther de-wa­ter­ing may be needed when build­ing foun­da­tions were in­stalled.

She said the wa­ter was spread across the park, rather than pumped into the nearby Avon-Heath­cote Es­tu­ary, to min­imise the po­ten­tial for sed­i­ment build up in the es­tu­ary and other linked wa­ter­ways.

The process com­plied with Christchurch City Coun­cil and ECan re­quire­ments.

De-wa­ter­ing was re­lated only to the con­struc­tion of the new school, and had no im­pact on fu­ture flood man­age­ment of the site.

IAIN McGRE­GOR/STUFF

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