On May 24^th, the Spreydon Heathcote Community Board hosted an information session on the Land Drainage Recovery Programme (LDRP) for our area.  Keith Davison and Peter Christensen presented to the group.  A very informative, well attended session gave specific insight into the challenges and scope of river damage following the earthquakes.  It was soon obvious that solutions will take time and funding to resolve, and will be very expensive.  The LDRP is setting in place short / medium and long-term strategies in its plans.

The goal of LDRP is to return flood risk to pre-earthquake levels, trying to find ways and solutions to prevent flooding.   Historically the Heathcote River has always flooded.  Several floodplain management strategies have been instigated over the years: Woolston Cut & Upper Heathcote flood plain ponding. Following the earthquakes there was a change in flood risk – areas.  Some had uplifted or subsided changing the way the water flowed across the Christchurch area.

What is the LDRP doing?

Assessment:

• Re-assessing the whole city and starting again. The river flows are not behaving as they used to because of changed ground and water levels.
• The LDRP is using detailed measurements to identify earthquake damage – the technical input data represents the ground topography and gives a new profile of the land
• Understanding the new way the land drains is challenging
• 100 different investigations were begun to determine options and solutions
• The effects of climate change and sea level rising need to be taken into account
• Expert opinions were sought from scientists in NZ and overseas esp The Netherlands

Investigations:

• Developing concept designs for repairs to banks and structures. Assessment of the banks from the confluence with the Cashmere Stream to Ensors Rd is currently underway.
• Upgrading the topography technical data of the Heathcote
• Conducting flood level surveys adjacent to the Heathcote river to determine properties at-risk to flooding
• Investigate options for flood mitigation in mid-lower Heathcote. This will be complex and difficult. LDRP will need to sort through the range of issues and solutions to get the best possible result.
• Develop further storage in the Upper Heathcote basin – Sparks Rd. Two new basins have been constructed. Further land in the area has been bought to increase water storage and reduce the risk of down-stream flooding.

Upcoming maintenance work

• All schedules are being reviewed to maximise spawning along the river: trout, whitebait.
• Scheduled bank cut, including vegetation within the channel after June 1^st 2016
• Seek authorisation to remove minor slumps prior to October (have been on hold due to spawning restrictions)
• Review weed harvesting schedule to optimise use of equipment.

What can we do?

• Ensure that rubbish is not dropped into drains
• Report any maintenance issues to the Council
  • Call 941-8999
  • Snap send solve app
  • If you are concerned about rising water levels, phone 941-8999 and ask for the Civil Defence Duty Officer to report your concerns

Conclusions

• The issues are complex
• Short-term solutions underway: Upper Heathcote storage, bank works & maintenance
• Longer-term floodplain management options being developed

Waste Water system

• Water has been getting in to the sewer system in heavy rain times. To help prevent this happening, the valves to keep the flows separate have been changed to non-return rubber valves, which will be much more reliable.
• Vented manhole covers have also been inserted to prevent the manhole covers popping open when large amounts of water are flowing. More work is on-going to stop storm water getting in to waste water during heavy rain events
• 50% of stormwater enters sewers from private properties (our houses)
• There will continue to be adaption to the changes as the river finds its new equilibrium

Thanks to the Community board for arranging this very informative session.  It is easy to underestimate the difficulties post-earthquake that changes to the ground and river areas create.  The LCRA will keep you posted on other information sessions as they are held.