Stormwater networks

Most of the storm water network is underground, which services approximately 42,000 connections. The storm water network is made up of approximately
  • 653,000 meters of storm water mains pipes. 
  • Diameters range from 0.75m to 2.4 meters. 
  • With lengths ranging from 0.5m to 680 meters.
Some of the existing pipes are over 90 years old. The network pipe system is constructed of a range of materials like, plastic, ceramic, cast iron, concrete, aluminium and steel which provides drainage for private connections and runoff from roads all over the city.​

Inflow and Infiltration

Infiltration and inflow refers to stormwater that has flowed into the wastewater network. It is very important that stormwater is not directed into the wastewater system, and that wastewater is not directed into the stormwater system as this can result in overloading of the wastewater system or untreated wastewater entering the environment. This can significantly affect public health, the system, and the environment.

One of the main ways to make sure this doesn’t happen is too.
  • Raised Gully Traps 
  • Plant trees or shrubs away from pipelines.
  • Locate pipe before digging or installing fence posts.
  • Regularly check for soggy or patchy spots in the lawn (maybe sign of broken pipe)
  • Make sure roof water is piped to stormwater and not to the gully trap.​

Stormwater Education

By disposing of everyday items correctly we can help to protect the environment. You can help by disposing of materials correctly to prevent blockages. Blockages can create stormwater overflows, flooding and damage to the stormwater network, which can cause pollution of the ​environment.

Hamilton City has placed an embossed image of the Giant Kokopu onto stormwater catch pits to help remind us that the water entering these discharges straight to our waterways. 

In 2008 school students in Hamilton were asked to write a story about our Kokopu with the author of the winning story getting to name the fish. As a result, Hamilton’s Kokopu is now called Rusty. 

Some everyday items that should not enter the stormwater system are listed below. You can help by disposing of these items in an appropriate way. 
  • Oils and greases
  • Rubbish
  • Baby wipes/disposable nappies
  • Hygiene products
  • Cleaning products/chemicals/paints
  • Food scraps
  • Paper and plastics
  • Paint rinse water

Stormwater Safety

Stormwater systems, whether they are open drains above the ground or pipes located underground are dangerous. They are designed to capture stormwater and can flood quickly and without warning. Stormwater is not treated and runs directly to receiving waterways and the Waikato river.


Manhole covers weigh up to 50KG eg (a motorcycle). When the drains get over full, manhole covers can sometimes be lifted and thrown by the pressure of water below. That means a person wading through floodwater risks falling into an open manhole full of water. Then, as the water begins to subside, it can rush in like a whirlpool, sucking you in.


A grate is a lump of cast iron weighing approximately over 50kg. If it dropped on you, it can cause serious crushing injuries. Don’t go lifting stormwater grates or lids, even if you can see a lost ball or other item just below. One slip could cause serious harm.

Don’t play in stormwater outlets

Stormwater drains can also be home to some pests like mice, rats, possums, cockroaches, flies and spiders. 

Also remember flowing stormwater and hidden debris can suddenly knock you off your feet and sweep you away, possibly into receiving waterways and the fast moving Waikato River.

For various reasons pollutants (such as sewage, chemicals, or runoff) sometimes enter into the storm water system, which can be toxic to human and animal health and can result in serious harm or even death.

If an animal or person gets caught in a stormwater drain or flash flood, phone emergency services immediately on 111.
Page reviewed: 12 Jan 2016 2:34pm