Storm Water Neutrality

If you are about to develop any site large or small you need to take into consideration Storm Water Neutrality. With new standards being introduced and stricter ruling on how you intend to cater for storm water neutrality having an understanding on this topic is becoming more relevant.

For the past 6 months all new developments require a solution for neutral storm water disposal. This means having a team behind you that is familiar with solutions to storm water disposal is crucial to ensuring your development stays on track and has no delays due to standards and expectations set by Councils and Wellington Water.

What methodology are you using?

When a development is considered, there is a focus on the amount of infrastructure and impermeable areas that will be constructed as this will dramatically impact the natural undulation of the land and existing storm water management. It is important to consider what is being constructed as nearly every vulnerable catchment area will have effects on neighbouring properties.

There are generally two existing Storm water management solutions in place for majority of suburbs, Storm water drainage is the predominant solution with drains leading underground resolving the bulk of smaller storms and weather throughout the year. During heavy rainfall events however this drainage cannot manage all the storm water that is formed and so a secondary solution is in place called overland flow paths or more commonly known as stormwater secondary flow paths. Other smaller solutions can be put in place dependent on the site such as ponding areas which can be naturally in place or built to assist with storm water management.

Wellington Water is now requiring all developments show that they are hydrologically neutral meaning that the post development of the stormwater run-off is no different than before the construction of dwellings and impermeable areas. The current accepted solution is a rainwater tank installed in the development to manage excess rainfall when storms come through. However other solutions are accepted when proven to manage excess rainfall for 1 in 10 year floods and 1 in 100 year floods.
Rain water tanks only manage rainfall from your roof catchment which means if you have a large amount of impermeable areas other solutions need to be considered when proving your development caters for 1 in 100 year floods. It is due to the additional need for stormwater management solutions when having large impermeable areas that Councils and Wellington Water ask that when designing your development you minimize your impervious areas so not to require additional solutions and to minimize the risk for flooding.

If you are considering a development make sure you take into account Storm water management during your design stage. Knowing all of the options to manage this is important as not all sites will have the space to have tanks installed on site which will call for more creative methods to manage your storm water run-off.

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