Useful information

Onsite Detention Tanks: Why Do You Need One?

Do you work on a site that’s prone to storms? If so, then an Onsite Detention Tank (known as an OSD for short) is now a requirement for you.

Why? Well, it’s a matter of safety really. OSDs are now compulsory for new or recently-renovated constructions or developments, so it’s important you swot up to ensure you continue to do everything by the book.

What is an OSD used for?

By now you’re probably wondering what an OSD is actually used for. So, we’ll tell you…

Simply put, then, an on-sire storm water detention tank is a means of detaining the storm water from your site to ensure everything you do is controlled in a safe manner.

Are you in the construction industry? If so, then you have a duty of care to understand not just why you’d need to use an OSD, but how to effectively maintain one, as well.

Can rainwater be collected safely, then?

Here in Australia, ever-evolving developments in construction (and the subsequent removal of much of the natural landscape) result in there being insufficient means to collect rainwater safely and effectively.  If you’re a land, company or home owner, this can present itself as flood risk; hard surfaces like pavements, roofs and site drainage mean an increase in not just the volume but the speed of storm water run-off.

So, you look to an OSD system, which can save you money and ensure you’re doing things properly.

Is an OSD cost-effective?

An OSD system can be extremely cost-effective, given that it acts as a preventative measure. Therefore, it can save you spending money later down the line on costly repairs as a result of storm water damage.

On top of this, an OSD system will help you claw back valuable time, which you can use elsewhere on or in your business.

While an above ground OSD system is generally costlier to construct, every site is different and there’s an ideal solution out there for you – be it an above or below ground OSD system.

Should you invest in an OSD system, then?

The answer is ‘yes’. After all, the capacity of storm water drainage systems can be limited.

If you’re in the middle of building a new property, OSDs will form a compulsory part of the planning and development process, and you’ll be pleased to learn they’ll save you money by reducing the risk of flooding.

Are you connecting to or developing a property that connects to a town water supply? If so, you’ll need to install an OSD system.

Properties which link to a town’s water supply include all commercial, industrial and special use (community, educational and recreational) buildings or structures, as well as town houses, villas, home units or other strata subdivisions.

Bear in mind that each lot within a dual occupancy must have its own OSD system, with individual owners being responsible for maintenance.

So, how do OSD systems work?

In short, OSDs provide somewhere for storm water run-off to be temporarily stored. What’s more, on-site storm water detention ensures the rate and volume off run-off can be controlled. This will reduce the risk of overload and ensure you’re operating in a safe and efficient manner.

Am I eligible for an OSD system?

Again, the answer is probably a big, fat ‘yes’ here. If you’re connecting to or developing a property that connects to the town’s water supply, you’ll no doubt need to install an OSD system. You’ll find that many buildings – from schools to town houses and villas – will already have systems like this in place, but it’s always worth checking.

What about the dimensions of an OSD system?

The required size of storage and rate of discharge is location dependent, but you can get in touch with your local council and hydraulic engineer for more information and special requirements.

And what about design requirements?

Your OSD system must be equipped to store run-off caused by a storm event of up to 100 year ARI for the site. It must also control the rate of discharge to ensure the system can handle additional run-off.

With that in mind, if you’re thinking of having an OSD system installed, you must first prepare designs that meet strict requirements. These must be prepared by a qualified professional well ahead of any installation attempt.

What should my OSD system do?

Your OSD system should control the rate of discharge to ensure downstream storm water assets can handle the extra run-off

Do I need approval and how do I get it?

To ensure you can have an OSD system installed, you must first gain approval.

You will need a certification of design by a chartered civil engineer. This will verify that the system has been designed to meet the calculated PSD and SSR. Alongside this, you’ll also need a plan and elevation of the OSD system with all dimensions, and you’ll need to know the location of the system in relation to your site.

Before you proceed, you’ll need a detailed design of the orifice, to include all the necessary dimensions, the maximum storage discharge rate specs, and the percentage of the site area that will drain to the street. This only applies in some cases, though.

To give you an idea of size, the orifice plate must be a minimum 200 mm x 200 mm flat stainless steel plate and 3mm thick. It should also not be less than 40 mm.

What about OSD maintenance?

Before you steam ahead and have an OSD installed, you must be aware that a certain level of maintenance will be required.

In advance of installation, ask yourself the following question:

Does your OSD system discharge directly into a council-owned drainage system?

If the answer to the above question is yes, you must get approval for the design of the tank. To do this, you’ll have to submit a raft of information to your local council, and you must do so well in advance of any construction work.

So, what information will you need? To begin, you’ll require verification that your design meets the calculated PSD and SSR, via a certification of design.

You’ll also need a detailed plan and elevation of OSD systems, along with relevant dimensions. Alongside this, you’ll need to know where you plan to locate your OSD, as well as submit a detailed design of the orifice that will contain it.

In terms of maintenance, you should keep on top of this to prevent potential problems occurring. What this does is ensure that if there’s a storm, the OSD comes to the rescue.

Does your OSD system discharge directly into a council-owned drainage system? If so, you must enter into a formal agreement with us to set out your ongoing responsibilities with regards to regular maintenance. The information must be stored on the title of the land and not lost over time, with the changing ownership of properties.

Where should the OSD be located?

The good news is this type of storage can either be installed above or below ground. It can also be installed in a combination of the two. Now here’s the more serious stuff:

  • It must conform to the current Confined Spaces regulation
  • It must feature step irons if the fall is 1200mm or more
  • Where there is a risk of gas build up or hydrostatic pressure, a release valve should be installed.

So, have you decided by now that an OSD system is for you? If so, do not hesitate to get in touch with our team and we can talk you through the construction process.