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.
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.
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.
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.
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.
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:
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.
For any enquiries about stormwater, please contact us.