Stormwater management is a critical part of your development project and has never been as important as it is today. Just ask your local council. The rules have tightened, the consequences of getting it wrong land on you, and the tank is the part of the answer that has to be sized correctly before anything goes in the ground.
Why development creates a stormwater problem
More development means more infrastructure, and more infrastructure means more impervious surfaces like concrete, asphalt and roofing. Hard surfaces like these allow little or no stormwater infiltration into the ground. Impermeable structures replace the vegetation and natural surfaces that usually soak up the rain and, as a result, increase stormwater flow into drains. The rain falling on a site after it is built is the same rain that fell on it before. What changes is where that rain goes. Ground that used to absorb it now sheds it, and it sheds it quickly. There are practical ways to manage impermeable surfaces, and the tank is usually central to them.
What that does to council systems
Council stormwater systems can be inundated without careful management, with a greater risk of flooding and erosion of waterways and coastal environments. A network is sized on assumptions about how much water will reach it and how fast. Every new hard surface that discharges straight to a drain moves the real figures away from those assumptions, and it does so one property at a time, which is exactly why the obligation lands on individual developments rather than somewhere upstream. This is why council regulations surrounding stormwater management have never been so stringent.
How a detention tank works
Our detention tanks remain empty except for during periods of rain. When it rains, the tank collects the stormwater and then gradually releases it at a council-specified rate into the local system. The goal is to discharge water from the tank without causing inundation and associated problems. Or, to be more precise, minimising the chances of inundation, because managing stormwater is one thing and managing nature is quite another. Note what the tank does and does not do. It does not reduce the volume of rain that fell on the site. It changes the rate at which the network has to deal with that volume, and rate is the variable that causes the trouble. This is where detention and retention part company.
Meeting your obligations on site
One of our stormwater detention tanks will help you meet your obligations safely and efficiently. So not only will you have the best stormwater management on your property, but you'll also reduce the pressure on the council stormwater system. All over New Zealand, and particularly in the larger centres, councils rely on effective stormwater management on a project-by-project basis. That reliance is deliberate rather than lazy. A network cannot be enlarged quickly enough to absorb every new roof and driveway being added to it, so the mitigation has to happen at the source. Promax detention tanks are up to the task.
Every council writes its own rules
Different councils will have diverse requirements for stormwater management. It's a bit like gaining resource consents for water storage tanks, where local authorities all over the country have their own rules. We must never assume that what applies in one place will apply in another. Council stormwater management plans will set out regulations that apply to a specific region, so liaising with the council early will help you stay updated with their expectations. It is the cheapest call in the project. Discovering at inspection that the tank was sized against the wrong rule is not a problem you can solve on site.
Sizing the tank
We have a range of devices and calculators that will help you determine the right size for your stormwater tank. This can be a potentially tricky calculation, but with our experience and knowledge, we can simplify things for you and ensure you meet your obligations. The inputs are specific to your site and to the rule your council applies, which is why a figure that worked on the last project does not simply transfer to this one. Rather than carry a number across and hope, run it through the stormwater detention calculator and let us check the result with you.
Talk to us before you specify
As you'd expect, Promax will work with you to take the stress and hassle out of this particular issue on your development project, from confirming the size through to getting the tank on site. It's just one of the ways we can guide you through the process of managing stormwater on your particular project, and it costs nothing to start the conversation early. Contact us for further information and advice to help you make the right decision, or call Promax on 0800 77 66 29.