Residential Stormwater Drainage

There is no such thing as “not possible” when it comes to residential stormwater management. Despite our extensive commercial stormwater experience and portfolio, no job is too small! Drainage NZ specialise in a large range of residential stormwater drainage applications including:

Onehunga soak holes
Charged stormwater systems
Residential water/rain tanks with first flush diverters (supply and installation)
Soak holes / Soak garden drainage.
Onsite stormwater management.
Residential treatment devices.
Surface water management and solutions
Flooding management and solutions.
Stormwater pumped solutions and chambers
Installation of channels and cesspits

ONEHUNGA SOAKHOLES

Soakage areas have limited stormwater reticulation, and are primarily located in parts of Ellerslie, Penrose, Onehunga, Mt Eden, Epsom, Mt Roskill and Mt Albert. Public soakage devices are provided for runoff from roadways in these areas, but individual property owners must construct and maintain their own soakage devices for runoff from private properties. The soakage devices allow stormwater to percolate into the ground, and generally consist of either boreholes into fractured rock or large holes filled with scoria.

Experience has shown that soakage devices have a high failure rate, often caused by dirty stormwater clogging the surfaces that the stormwater soaks into. This Manual addresses this problem in three ways. Firstly, if the total paved area on the site exceeds 20 m2 then runoff from these areas must be treated before it enters the soakage device, and worksheets are included for sizing pre-treatment devices. Secondly, all runoff from roof areas must pass through a settling device. Thirdly, guidelines are given to assist with the operation and maintenance of all these devices.

Finding sufficient space for soakage devices can be difficult, especially if soils have a low capacity for soakage. To assist with situations such as these, the Manual includes a methodology for sizing rainwater tanks. The rainwater tanks provide a temporary storage space for rainwater, and allow a reduction in the size of soakage systems. If a permanent storage space is also included in the rainwater tanks, they can be used to supply some of the water required for household use. The rainwater tanks must have an orifice on the outlet, and this must be sized to be compatible with the soakage system.

Drainage NZ can provide the following solutions:

Nominal Soakhole: Installed beneath a grassed area–This example has an inspection well topped off with an alloy toby box.
Onehunga Soakhole: Installed beneath a grassed area, with manhole visible
Filter-strip Soakhole
Rain-garden: one example is receiving stormwater from a car parking area.
Rockbore Soakhole Installed beneath the pavement of a high density development.

Circumstances that Require Resource Consents
In general, soakage systems in Auckland City require resource consents in the following situations:

1. Properties with greater than 60% cover by impervious surfaces require a resource consent.
2. Properties larger than 1000m2 require a resource consent.
3. Industrial and trade processes require a resource consent.
4. Some soakage bores may require resource consents.
5. All stormwater systems in Auckland must comply with the Development and Connection Standards

For more information please down the Auckland Soak hole Design Manual

Water Harvesting and Rain / Water tanks

Rainwater harvesting is the gathering and storing of rainwater. Rainwater which is collected from a clean impervious surface in open country is one of the purest forms of natural water. Rainwater harvesting systems provide a source of soft, high quality water and utilises a source which would otherwise be wasted. The system will reduce the usage of other sources and will be cost effective, with the metering of water becoming more common around New Zealand.

Rooftop catchment: This form of harvesting rainwater is very common in New Zealand and is also becoming popular in the Auckland area. It is a simple process where rainwater is collected in a storage tank at the edge of a roof. The amount and quality of water collected will depend on the size and type of roof. The best quality water will be collected from roofs constructed with galvanised corrugated iron, aluminium, copper, tiles and slates. Roofs and guttering should be cleaned regularly to remove dust, leaves, and bird droppings, to ensure that the best quality of water is maintained. Consideration needs to be given to the quantity of water a household may require. This can be calculated on a yearly basis with the allowance for seasonal variations. Yearly rainfall tables are available. These can be used in conjunction with the roof catchment area to determine the annual water harvest. Storage tanks needs to be large enough to hold all water collected during the heavy rain periods for use through an dry months.

Surface Water Catchment and Management
Water flowing over the ground’s surface before collection is referred to a “surface water”. The catchment area for surface water is the point where water is drawn for processing. The catchment area is generally plentiful in water which often will require manmade structures to create a dam. The dividing line between two catchment areas is called the “watershed”. A range of mountains forms the watershed with a catchment area on either side.

Drainage NZ have extensive experience in overland, lowland and underground water management including:

Installation of Wingwalls and rip-rap’s
Supply and installation of driveway cesspits, channels and treatment devices
Subsoil drainage design and installation

Whether it’s a large or small drainage job, Drainage NZ will ensure the job is done right and to your 100% satisfaction! All our solutions come with extended warranties and certification. Drainage NZ have 10 million dollar public liability insurance and are master drainlayers giving you the assurance and confidence you need, knowing you have the right drainlayers on the job.

For more information or an obligation free consultation please call 0800 Drainlayer.