Kapiti Coast Drainage Channel Assessments

By working with the community and the Kapiti Coast District Council Cardno has helped the Council to manage its stormwater network so flood risks are minimised.

Since 2015, severe weather events have flooded 800 locations on the Kapiti Coast and at least 25 per cent of coastal properties face a flood risk from a one-in-one-hundred-year event.  

As much of the stormwater network comprises, or relies upon, the functioning of open stormwater channels, the Kapiti Coast District Council engaged Cardno to assist with resource consenting for maintenance of the extensive stormwater network.   

Many of the stormwater channels in the area are relics of farm drains created in the early 1900s to convert marsh and swamp land to pasture. Modelling confirmed increased capacity of these channels and identified that removal of accumulated sediment and in-stream vegetation was needed to adequately convey flow.  

The drainage system extends from farmland through industrial and residential areas and into wetland environments, resulting in different issues for each section. Some sections of the drainage system are used by the public as a food source, while others are located on land dedicated to scientific reserve.  

Cardno prepared an application to the regional council for the necessary resource consents and to provide the requisite environmental services. Cardno also successfully consulted with the regional council, iwi, Department of Conservation, and affected parties. Issues covered in the consultation and the application for resources included: ecology and fish passage, sediment discharge, flood hazards, cultural and heritage effects, and landscape and natural character effects.   

Services provided by Cardno’s Environment and Water team included planning, freshwater ecology, assessing sediment for potential contamination, landscaping and hydrology.