What is a stormwater catchment management plan (CMP)?
A stormwater catchment is an area of land where rain flows into a common river, lake, or other body of water.
New Plymouth District has 13 urban stormwater catchments, and developing a management plan for each of them is the first and most urgent task defined in the Stormwater Roadmap.
The scope of our CMPs is restricted to the urban portions of the catchments (these are the areas managed by NPDC) and to the issues caused by the runoff from local rainfall.
The CMPs capture the current state of the urban stormwater network for each catchment and where the challenges are, and identify the opportunities to address these challenges. They are primarily focused on stormwater and its effects on flood risk, people and the environment, but also integrate other aspects when appropriate, like where there is significant inflow to and overflow from the wastewater network.
In some catchments like Waiwhakaiho and Waitara, the control of flooding risk caused by the rivers is managed by Taranaki Regional Council.
Stormwater issues involve more than the existing piped network. Understanding the causes of flooding requires understanding the natural water flows across a landscape, the role of manga (streams and creeks) and awa (rivers), and the role of the built environment. Māori have a valuable role in this understanding through matauranga (knowledge) and kaitiakitanga (guardianship), as do local residents, and businesses who have experienced stormwater issues.
The proposals in the CMPs to address stormwater issues try to incorporate a holistic approach, based on the comprehensive understanding that the CMPs provide. They may range from upgrades to the piped network, to restoration of streams and wetlands, or managing land development to prevent specific issues in a given area.
We are starting in Waitara due to its significant and ongoing issues with stormwater and flooding. Expected publishing dates for the CMPs are:
There are four main reasons for ponding and flooding.
The majority of homes and commercial buildings in Waitara have minimal risk of flooding. We’ve identified 115 properties that would flood in a one per cent AEP storm (water at or above the floorboards) and another 429 that are at some degree of risk; that comprises about 13 per cent of habitable dwellings (homes and businesses) in Waitara.
We are working to lessen the flooding hazard where possible, such as in eastern Waitara with stormwater infrastructure improvements and the reopening of Tangaroa Stream to reduce the risk of flooding during heavy rainfall. We’re also investigating where existing infrastructure, such as roadside swales, aren’t working as well as they should and what can be done to improve them.
While we can’t build our way out of the fundamental problems of flat land and buildings located in areas of natural flow paths, we can use this information to make better plans for future housing and commercial developments, stormwater improvements, and emergency response during a flood. Part of this work includes developing a digital stormwater model, on which we can run different scenarios of rainfall to see where problems will arise in Waitara. This will help us ID priority areas for stormwater improvements.
Kerb and channel aren’t the solution for many areas in Waitara. For instance, they won’t fix the problem of water running off roads and down driveways, or of excess water not draining away because the land is flat. But as funding becomes available, we will establish kerb and channel in areas that will benefit from them.
We know that a warming world is driving more intense rainfall and that these events are occurring more often. However, this catchment management plan is based on identifying properties at risk during a one per cent AEP flood.
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Page last updated: 09:30am Thu 27 March 2025