8 Nov 2017

A multimillion-dollar package of work aimed at lessening the impacts of Heathcote River flooding has got the backing of the Christchurch City Council’s Infrastructure, Transport and Environment (ITE) Committee.

After considering a staff report, the Committee today decided to recommend the Council push ahead with work on a number of floodplain management projects that will help reduce the risk of over 200 homes near the Heathcote River flooding.

The Heathcote RiverThose projects include:

  • Completing the design and construction of four new storage basins in the Upper Heathcote area.  The storage basins will store flood waters during the peak of a storm and slowly release them after water levels downstream have dropped. Construction of all four will be under way or completed in 2018.
  • Dredging the Heathcote River to remove silt that has built up in the river over the years and deepening the channel so it can handle bigger flows of water. It is estimated about 60,000 cubic metres of material needs to be removed from the river channel.
  • Investigating the technical feasibility of building low stopbanks upstream of Hansen Park to reduce the risk of frequent underfloor flooding in the most vulnerable areas.

The Committee has also recommended the Council use the Flood Intervention Policy to help property owners whose very low lying homes frequently flood and are unlikely to gain enough benefit from the proposed flood mitigation works.

“Between 25 and 35 houses along the Heathcote River have been identified as flooding multiple times since the earthquakes – some of them as many as four times,’’ says Council Land Drainage Manager Keith Davison.

“To provide relief to those worst affected property owners, we have recommended the Council use the Flood Intervention Policy. The Committee has taken our advice on board and will be recommending that course of action to the Council,’’ Mr Davison says.

The Flood Intervention Policy was put in place in December 2015 to help property owners whose homes frequently flood since the earthquakes and are unlikely to benefit in a timely manner from planned flood mitigation works.

That help can take the form of localised drainage works or housing raising, although in some cases, as with the Heathcote, the Council might offer to purchase the property.

Preliminary estimates put the cost of implementing the Heathcote floodplain management projects at about $72 million.

The low stopbanks are not included in those costings.

Of the $72 million, about $28 million is already budgeted for in the Council’s Annual Plan. The remainder will require funding through the Council's Long Term Plan and its Land Drainage Recovery Programme.

The full Council will consider the Committee’s recommendations when it meets on 23 November.