Last week, members of the Council's Land Drainage Recovery Team presented an update on Heathcote River flood mitigation work to Heathcote community and residents groups and the Hagley/Ferrymead Community Board.

We thought you might be interested in hearing what was discussed around flood mitigation work that's happening, and what's being planned.

What's being looked at?

The Land Drainage Recovery Programme, or LDRP, aims to reduce flood risk across the city to at least pre-earthquake levels.

The programme recognises the lower Heathcote and Heathcote Valley as priority areas for flood risk investigations and mitigation works.

We are fast tracking investigations and mitigation works, with a big commitment of funding and resource, but it will take many years to implement the flood mitigation works.

Flooding has always been an issue along the Heathcote River. Previous investigations into Heathcote River flooding have seen the development of floodplain management strategies, and these have led to:

• Planning rules, such as the District Plan, high hazard and flood ponding management areas

• The Woolston Cut

• Storage basins in the upper Heathcote to mitigate development

Although flooding has long been a problem, Christchurch's land drainage issues post-earthquakes are hugely challenging - so much has changed with land subsidence and damage to waterways and land drainage infrastructure.

The LDRP team is looking at the change in flood risk, considering things like land damage, tectonic shift and changing streambed slopes that have increased the flood risk to properties and homes.

Much work has gone into a condition assessment, to understand the damage to the city’s land drainage network. The city-wide assessment is nearly complete, and from this, further maintenance works, in addition to those already underway, are being prioritised.

Investigations underway for the Heathcote River include concept design for repairs to banks and structures to repair earthquake damage, while also providing greater resilience and improving habitat. We are also working to upgrade the Heathcote River flood model, adding in more detail to get a better understanding of flooding issues, and how best to mitigate them.

We are looking at the benefits identified in previous floodplain management strategies, particularly storage in the upper Heathcote, and looking at how to fast-track the most beneficial ones.

Essentially, we need to do thorough investigations to understand the risk, prioritise those most at risk, and develop sensible area-wide solutions that offer the most benefit, to the most people.

What's being done?

We are now starting to see implementation of LDRP recommendations in the Heathcote catchment.

Two new basins are being constructed on Sparks Road to increase flood storage.

The Council has also purchased land in Hendersons Basin for additional flood storage. This significant area of land – 37ha – will allow for storage facilities to be constructed to help reduce increased post-quake flood risk in the upper and middle reaches of the Heathcote River.

Click here for more information on Eastman Wetlands, Matuku waterway and Bells Creek mitigation work.

Maintenance works planned over the coming months in the main river channel include:

• A scheduled bank cut, including any vegetation within the channel, will be started next month  (this was delayed this year due to spawning restrictions in the Resource Consent)

• We are seeking authorisation to remove the minor earth/grass slumps in the mid-reaches of the Heathcote River prior to October (special authorisation is required for works before October due to spawning restrictions in the Resource Consent)

• We are reviewing weed harvester scheduling to see if can optimise use across three rivers, and/or what the cost and benefits are of a second harvester.

Maintenance – what can you do?

• Ensure rubbish is not dumped into drains

• Please report any maintenance issues or flooding concerns to Council by calling 941 8999, or using the Council’s Snap Send Solve app.

When the city is in line for heavy or sustained rainfall, please keep an eye on the Council’s Facebook page for any weather developments, flood warnings and precautions.

Our aim, wherever possible, is to reduce flood risk through area-wide mitigation schemes. Where this can’t be done, the Council will offer assistance to property owners whose homes are at risk from flooding during regular rainfall events, where the earthquakes have worsened this risk, and the home will not benefit from timely, area-wide engineering works to reduce the risk.

Flockton is the first area where this policy has been applied, having been through a long process of investigation and flood mitigation design, and understanding which properties will benefit from timely, area-wide mitigations, and which won’t.

In other high priority flood risk areas like the Heathcote catchment, once the LDRP has completed flood risk investigations, if there are still properties at high risk that won’t benefit from timely area-wide mitigation, the Council will offer the same assistance to these property owners.

Find out more infomation on this policy here.

Flood risk and flood mitigation are complex issues. We are focused on quick wins, such as storage in the Upper Heathcote, bank works and maintenance, while working on thorough investigations, and sensible, area-wide solutions that offer the most protection, to the most people.

There’s been a lot of talk about floor levels lately and a lot of confusion about the height your floor needs to be to protect your home from flooding.

Check out Newsline for some answers to some of the questions we have been hearing, and a video with the Council’s General Manager Consenting & Compliance, Peter Sparrow, where he lays out the basics around floor level heights.