Parramatta council and OSDs

There is a house we're interested in putting in an offer. There are a few grates at the backyard for the OSD. Is anyone familiar with Parramatta council whether these grates/OSD can be covered? We are wanting to build a floating deck to cover the grates, certain sections of the deck will have hinges/trap door to allow access to these grates. We are wondering if there would be any issues in building over the OSD system. It appears all new developments in the Parramatta council requires an OSD, so almost every house we've inspected have them in the backyard or driveway.

Thanks

 

What do you think that the OSD does & the purpose of the grate? Where will the water go once the pit exceeds the capacity?

When you answer these, you will be better informed.

 

Not all development need OSD in Parramatta. OSD is needed when your hard surfaces exceed a certain sqm. I think 230sqm.

Ask vendor to provide you with old DA. It must be a DA condition to not obstruct the OSD area. OSD area flood, and therefore flood warning sign is needed.

legally you cant, but many people do it illegally. It is all fine until your neighbour lodges a complaint to Council.

 

From what I can see, once it reaches a certain level it will then be drained into the main stormwater pipes.

 

From what I've read, all dual occ in Parramatta council requires an OSD whether it is needed or not. It is definitely not in a flood zone, almost every Duplex we've inspected have an OSD (Those built in the last 3 years).

So I guess, most of the ones we've inspected would have hard surfaces larger than 230sqm.

 

No, OSD is designed to reduce the rate of discharge to the council stormwater system. It doesn't stop the flow until it's full, water levels increase during a rain event and it continuously discharges.

 

The purpose of OSD is to reduce the flow of stormwater, so it does not cause flooding or erosion in low-level areas. Regardless of your property is flood affected or not. You need OSD if hard surfaces increase over 230sqm. All duplex need OSD is because the Parramatta council only allows duplex on land rather than 600sqm with 0.5 FSR. So the hard surfaces will be over 300sqm (roof, driveway, carport, paved area, alfresco, decking etc) therefore OSD is needed.

Water level will increase in extreme weather conditions and water overflow from the grate. In Parramatta area, you see lots of duplex with OSD basin located in the front (next to the driveway). OSD basin in front look ugly and very little you can do about it. You may see flood sign posted on the OSD basin area.

 

Thanks, the OSD covers a large area, can a floating deck still be built on top it it, but not covering the grates?

 

More likely answer is no but check the title for positive covenant and DA condition may impose a restriction. Some information from Parramatta Council's policy

OSD systems are structures intended to control site discharges over the entire life of the development. To guarantee the system's continued operation, it needs to be protected from alteration and regularly maintained.

Prior to any occupation certificate being issued, the OSD system and associated floodways and flowpaths need to be legally protected. This is achieved by applying a restriction on the use of the land and a positive covenant over the lot in favour of
Council.

The OSD system is an integral part of the development and the effectiveness of OSD system in controlling run-off from developed sites is a function of its maintenance.

The proponent must ensure that the tank can be readily inspected & maintained by
considering the following:

a) The invert of the basin should be well graded to prevent permanent ponding.
b) The orifice plate is to be screened.
c) The basin should be located in a position such that it can be easily inspected
and accessed for cleaning.
d) The basin is to be protected by a restriction and positive covenant requiring the
owners to carry out periodical maintenance.