New Zealand Construction Regulations

Installation and Maintenance of Stormwater Handling Systems

Overview of Stormwater Handling Systems

• Stormwater is the runoff of water from urban surfaces, such as roofs and driveways, from rainfall or melting snow
• It needs to be managed to prevent flooding, erosion, and pollution of waterways
• Stormwater drains and handling systems are designed to control the flow of stormwater and prevent damage to buildings and property

Legislation, Standards, and Codes

Building Act 2004

• Provides for the regulation of building work, licensing regime for building practitioners, and performance standards for buildings
• Ensures that buildings are safe, healthy, and sustainable

Health and Safety at Work Act 2015

• Places obligations and responsibilities on everyone in a workplace to take care of their own health and safety, and the health and safety of others
• Applies to people conducting a business or undertaking, officers, workers, and visitors

Plumbers, Gasfitters, and Drainlayers Act 2006

• Ensures the competency of plumbers, gasfitters, and drainlayers to protect the health and safety of the public
• Establishes the Plumbers, Gasfitters and Drainlayers Board to regulate the industry

Plumbers, Gasfitters, and Drainlayers Regulations 2010

• Describes legal requirements and pathways to gaining registration as a drainlayer
• Sets down fees and examination details for registration

Resource Management Act 1991

• Covers sustainable management of natural and physical resources
• Ensures protection of the environment and sustainability for future generations

AS/NZS 3500.3:2015 Plumbing and Drainage – Stormwater

• Sets requirements for materials, design, installation, and testing of roof, surface, and subsoil drainage systems
• Complies with the New Zealand Building Code as an alternative solution

Stormwater Collection Systems

Surface Water Collection

• Involves collecting surface water from roofs and driveways
• Includes design, installation, and maintenance of surface water collection systems

Sizing Stormwater Drains

• Factors to consider: rainfall intensity, catchment area, runoff coefficient, and drain size
• Calculations involve determining rainfall volume, flow rate, and drain size

Installation of Surface Water Collection Systems

• Involves positioning and installing collection systems, including channels and grates, slot drains, and intake and outfall structures
• Requires testing and commissioning of systems

Intake and Outfall Structures

Intake Structures

• Involves designing and installing intake structures, including stormwater intakes and natural watercourses
• Ensures that intake structures can handle flow rates and velocities

Outfall Structures

• Involves designing and installing outfall structures, including stormwater outfalls and territorial authority stormwater systems
• Ensures that outfall structures can handle flow rates and velocities

Subsoil Drainage

Types of Soil and Subsoil Drainage

• Involves understanding types of soil and their permeability
• Includes designing and installing subsoil drainage systems, including branch subsoil drains and water tables

Design and Installation of Subsoil Drainage Systems

• Involves designing and installing subsoil drainage systems, including spacing for branch subsoil drains and diverting groundwater

Sumps and Maintenance

Types of Sumps

• Includes type-one surface water sumps and type-two sumps
• Involves understanding sump design, installation, and maintenance requirements

Maintenance of Stormwater Handling Systems

• Involves regular maintenance of surface water collection systems, sumps, subsoil drainage systems, and intake and outfall structures
• Ensures that systems are functioning as designed and do not cause pollution or damage to property### New Zealand Building Code Clause E1 Surface Water

• The primary document for installing stormwater drainage in New Zealand is the New Zealand Building Code Clause E1 Surface Water. • NZBC Clause E1 consists of three main parts: Code requirements, Verification Method E1/VM1, and Acceptable Solution E1/AS1.

Verification Method E1/VM1

• E1/VM1 describes how to determine the volume of water arriving on a building site from an upstream area. • It includes allowance for a secondary flow path and for surface water disposal to a soak pit. • Suitably qualified people (as per paragraph 1.0.7 of E1/VM1) must carry out E1/VM1 Surface Water.

Acceptable Solution E1/AS1

• E1/AS1 includes requirements for drainage materials, construction requirements, and sizing of drains, downpipes, and roof gutters. • It is limited to buildings and site work with a catchment area of no more than 0.25 hectares, and those that meet specific conditions.

Surface Water Collection Systems

• Surface water collection systems include pre-made channels and grates, kerb and channels, or half-round tiles. • These systems are intended to collect and direct surface water flow.

Surface Water Drainage

• Surface water drains are intended to carry surface water to an outfall, and are normally laid below ground level. • The design of a surface water control system must consider location, environmental requirements, permeability of surface materials, rainfall intensity, and duration.

Sizing Stormwater Drains

• Stormwater drains must be sized appropriately to handle variable flow rates. • Sizing factors include minimum drain size (85mm), catchment area, and rainfall intensity. • Drains may become pressurized during high rainfall, causing water to flow back out of sump gratings.

Storms and Drains

• E1/AS1 Surface Water requires drains to be capable of handling the rainfall from storms. • Drains must be of sufficient size and gradient to handle the rainfall from a storm with a 10% probability of occurring annually.

Rainfall Intensity

• Rainfall intensity varies across different areas of New Zealand. • A listing of rainfall intensities can be obtained from the NZBC E1 Surface Water. • Calculating rainfall volume involves multiplying the catchment area by the rainfall intensity.

Modified Catchment Areas

• The modified catchment area is a number that relates to the true catchment area and rainfall intensity. • It is calculated by multiplying the true catchment area by rainfall intensity, and then by 0.01.

Drain Size, Ground Contours, and Gradient

• When designing a surface water or stormwater system, the minimum gradients allowed should be identified. • Ground contours affect the rate of run-off of a particular collection area. • Slope corrections for run-off coefficients are used in calculations for sizing of stormwater handling systems.

Run-off Coefficients

• Run-off coefficients represent the effects of infiltration, storage, evaporation, natural retention, and interception on rainwater run-off. • They are used in the calculation of surface water run-off and assume saturated ground conditions.

Installation and Positioning

• Manufacturers provide installation requirements or guidelines, including recommended embedment and minimum cover requirements. • Surface water collection systems must be installed exactly as designed, and any departure from the approved plan leaves the drainlayer liable for any problems. • The system must be positioned with consideration for secondary flow paths to prevent flooding of buildings.### Surface Water Collection Systems

• To install a surface water collection system, excavate a trench and compact 50 mm of sand for the base.
• Lay the system according to the manufacturer's instructions, with a gradient of approximately 1:70.
• Discharge the system to a stormwater sump to collect silt and debris.
• Surround the system with concrete if it is subject to vehicle traffic.

Channel and Grate Systems

• Channel and grate systems require a concrete haunching or embedment.
• The system discharges to a yard sump, which is the demarcation point where drainlaying work begins.

Slot Drains

• A slot drain has a narrow opening at the top with slits to allow water to flow in.
• The drain then discharges into a 90 mm stormwater pipe.
• The slot drain grating may be installed level, while the drain itself can be fitted with a fall.
• Some slot drains can provide drainage at a level threshold, but must still keep external moisture out of the building.

Drain Leakage Testing

• Perform a drain leakage test on an installed water drain using a water test, low pressure air test, or high pressure air test.
• If a concrete drain is installed, it must be soaked for 24 hours prior to testing.

Intake and Outfall Structures

• Intake and outfall structures are designed to carry surface water to an appropriate outfall using gravity flow where possible.
• They must avoid the likelihood of blockages, leakage, and damage from loads or ground movements.
• Intakes can include kerb and channel sumps, silt traps, sumps, chambers, and watercourse entry wingwalls.
• Grates or grills remove floating and larger suspended solids, while traps in sumps allow for heavier materials to collect.

Stormwater Outfalls

• A stormwater outfall is the part of the drainage system that receives the water.
• Examples of outfalls include natural watercourses, soak pits, the Territorial Authority stormwater system, and the downstream side of a watercourse culvert.
• Care must be taken when discharging directly to rivers or streams to prevent pollution.

Soak Pits

• Soak pits are used to dispose of surface water by soakage.
• They require a procedure to determine the soak pit requirements for surface water disposal.
• The soakage system and any sub-surface drains need to be higher than the water table.
• A soak pit must be enclosed in filter cloth or geotextile materials to prevent soil infiltration.

Retention and Detention Tanks

• Retention and detention tanks are large-capacity underground tanks that control the flow of stormwater run-off.
• Retention tanks store stormwater for household use or for the garden during periods of water restrictions.
• Detention tanks slow the flow of stormwater to prevent overloading of the disposal system.
• Both types of tanks may be made of pre-cast reinforced concrete, corrosion-resistant metals, or high-density polyethylene.

Watercourse Drainage

• Watercourses are open drains that occur naturally as depressions in the ground.
• They may be piped to improve the surrounding land or to pass under roads.
• The secondary flow path must be allowed for when designing a building.
• Piped watercourses are the responsibility of the landowner and may require a Building Consent and a Resource Consent.

Design and Materials

• A piped watercourse has seven parts: bedding, pipe installation, intake structure, outfall structure, haunching, sub-soil drainage, and backfill and finished surface.
• The type of pipe used depends on the diameter needed, its location, and the gradient it will be laid to.
• The design of a piped watercourse is usually done by an engineer.
• The diameter of the pipe is calculated by mapping the catchment area above the drain and adding any other flows.