The Napier City Council provides and maintains a stormwater disposal system for the city with the aim of minimising the effects of flooding. The system consists of open drains, stormwater mains and pump stations with about three quarters of the city reliant on pumped systems for stormwater drainage.
The council sets and maintains standards for stormwater reticulation and appropriate levels of flood protection for the city. The system is maintained to ensure a minimum of downtime and a full 24 hour, seven day a week emergency capability.
Napier city's stormwater drainage system can be divided into 15 catchment areas. Of these, 12 areas are each served by a pumping station. There are four catchment areas which are exclusively rural, six exclusively urban and the balance are of varying ratios of urban and rural.
The urban catchments are the responsibility of the Napier City Council which maintains drains and pumping systems that serve the urban area or those parts of the drains within the urban area. The majority of the other catchments fall under the jurisdiction of the Heretaunga Plains Flood Control Scheme maintained by the Hawke's Bay Regional Council, except for those in Bay View, which are under city council control.
The urban stormwater system is being continually upgraded. The current design standard requires the system to be designed to cater for the type of storm the city might expect to experience once in every 10 years in such a way that only limited surface ponding results. Increasing infill and greenfield developments have added more buildings, driveways, roads and sealed surfaces within the city boundaries, resulting in greater volumes of water running off the hard, impermeable surfaces and putting pressure on the existing stormwater and pumping systems. Up until 1996, the system was based upon a two year return period, meaning the city had a 50 per cent chance of stormwater ponding in the streets each year. There is now about a 10 per cent chance of similar ponding in any one year, known as a 10 year return standard.
It is a huge and very expensive task that will take decades to increase the stormwater system's capacity from the old design standard to the new design standard. The Council has been allocating funding for this purpose ever since the new standard was introduced.
During floods, priority is given to pump station operations, in particular cleaning the screens free of weed to allow the pumps to operate to their peak capacity.