Stormwater

Kāpiti Coast district's stormwater network is made up of over 8000 stormwater pipelines, with a total length of more than 210km and over 3300 access manholes.

Open waterways

All open waterways maintained by council are managed with an electronic database that automatically generates a maintenance inspection schedule. The frequency of inspection and clearing is based on the level of risk that flooding could cause in the area, as well as past experience and the weather.

In general, urban drains have more potential to cause damage in flood events, so they are inspected more frequently than rural ones. The impact of weed growth in and around waterways is affected by seasonal weather conditions, so the frequency of inspection varies between monthly, three monthly, six monthly and yearly.

Council inspects and maintains 45km of open waterways, which includes 118 sections of open drains. It also inspects and clears stormwater flap gates, which prevent backflow, throughout the district.

Controlling vegetation

Clearing vegetation from drains and stream beds reduces the risk of flooding. Two methods used for vegetation control are hand-cleaning and mechanical excavation.

Weed-spraying is not carried out because of concerns about the environmental impact on waterways.

Mowing around waterways is carried out on a regular basis.

Maintenance

All stormwater pipe inlets and outlets are inspected and cleaned quarterly, as well as after heavy rainfall. Areas with high levels of sediment, such as the Waikanae hill catchment inlets, are inspected and cleared monthly.

Beach outlets are inspected and cleared monthly with the exception of Paraparaumu Beach between the Waikanae River and the Wharemauku Stream. These are inspected and cleared on a weekly basis to prevent sand build-up which blocks the pipes and could cause flooding to residential properties.

Many public stormwater enquiries are received every day, including information requests on floodzones, land contours and house flood risk. Many of these need further investigation including site visits or other research, and often result in physical works being carried out.

Council responds to storm damage with network improvements

Flooding

Assessment of flood damage is carried out by council, on a case by case basis, to determine if a stormwater network contributed to the flooding so the necessary maintenance can be carried out.

We've developed detailed maps of where we think stormwater will go when there's a 1 in 10 year storm event or when there's that really big 1 in 100 year flood. To view these maps and supporting information, go here.

To find out how to be prepared should flooding occur, go here.

Strategy

Storms and elevated groundwater levels in 2003/04 increased community interest and raised important issues about overall links between urban growth management and stormwater.

The Council responded by bringing forward the stormwater review with its focus on high level issues including:

analysis of long-term climate change impacts and implications for levels of service choices;
assessment of implications for existing stormwater infrastructure capacity standards;
assessment of the implications for, and relationship with, development management;
reviewing the prioritisation methodology to give greater emphasis to groundwater issues;
reviewing site specific concerns.

Climate change implications for stormwater reticulation and stop banks are potentially very significant and include an increased frequency and/or volume of system flooding; increased peak flows in streams and related erosion; groundwater level changes; saltwater intrusion in coastal zones; changing floodplains and greater likelihood of damage to properties and infrastructure.

Stormwater and you

The Council's programme of stormwater work doesn’t involve works on privately owned properties or buildings themselves. And, although Greater Wellington Regional Council oversees the maintenance of a lot of our rivers and streams, we also count on people taking responsibility for their own homes and sections by clearing hazards as they crop up. Here’s a quick list of things that you can do to try to prevent and reduce damage to your section or home next time a storm blows through Kāpiti:

1. Create on-site water storage on your property. Store excess water during a heavy rain event by diverting it into a storage tank so that already under-capacity pipes aren’t overwhelmed by too much water at once. Once the storm has passed, you can let the excess water out once your water pipe is clear.

2. Maintain (and fix) your downpipes between extreme weather events. If you notice leaves, twigs, or garbage blocking a gutter, spout, or downpipe on your property, take a moment to clear it out and bin it before it becomes a real problem during the next heavy rainfall.

3. Do regular tree maintenance on your property. By keeping a regular check on the trees on your property, you can spot if roots have begun to grow too close to pipes or if their dropped leaves have blocked a drain. Rake up excess leaves as they fall, and watch for roots encroaching on pipes.

Discarded litter is a contributing factor to flooding during storm events as it can clog sumps so if you notice litter on the ground pick up and bin it, or if sumps are clogged, give us a call on 0800 486 486 and we’ll sort it out.

For any enquiries about stormwater, please contact us.