New Zealand; Rain Garden Owner's Manual - North Shore City Council

8/3/2019 New Zealand; Rain Garden Owner's Manual - North Shore City Council

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Rain Garden

Owners Manual

Property Address

Street name and number:

Suburb:

Note: This manual should be handed over to the

new owner whenever the property is sold.

www.northshorecity.govt.nz


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Rain Garden Data(To be completed by the rain garden installer or property owner as appropriate)

Note: This information is required by the Council for entry into the On-site Stormwater

Management Devices database.

Table Of Contents

1. Introduction 1

2. Purpose of Rain Garden 1

3. Rain Garden Operation 2

4. Operation and Maintenance Requirements 3

5. Contacts 4

Annexures

1. Rain Garden Drawings

2. Rain Garden Location Plan

3. Proprietary Products Operating and Service Instructions

Property address: Street name & number

Suburb

Date of completion

Resource consent number

Building consent number

Rain Garden Details

Impermeable area roofs (m2)

Impermeable area paving (m2)

Permeable area (m2)

Surface area of rain garden (m2)

Nominal depth of rain garden (mm)

Kerb outlet yes / no


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Hard surfaces created as part of urbandevelopment generate increasedstormwater runoff and pollutant loadswhich are ultimately discharged via thepiped stormwater network into streamsand the sea. The increased flow ofstormwater can overload the downstreamnetwork causing flooding. Increasedstream flows accelerate the erosionof stream banks resulting in damage

to adjacent properties and the releaseof sediment which is later depositeddownstream or in the sea causing harmto the stream and marine environment.

Rain gardens capture stormwaterrunoff from the roof and/or pavedareas of the house. The water is filteredas it percolates through the soil andplants and it is then released slowlyto the stormwater outfall via an underdrain. Overall stormwater volumes are

reduced by way of evapotranspirationand infiltration. The combination offiltering, reduction in the total volume ofstormwater runoff from the property andthe attenuation (reduction) of the peakflows contributes significantly towardsthe protection of streams from erosion,reducing the amount of contaminants andsediment washed into the rivers and seaand alleviation of flooding in downstream

catchments.It is accepted that rain gardens willoverflow in sustained, heavy rainfallevents. However, periodic flooding is anatural process and would occur evenin the absence of development. Streamsare able to tolerate these infrequent,high flows as they have a chance torecover and stabilise between events.The greatest benefits of rain gardens areexperienced during the high frequency,

1. Introduction

3. Rain Garden Operation

2. Purpose of Rain Garden

The purpose of this document is toprovide the property owner withinstructions and advice on how tooperate and maintain the rain gardeninstalled on their property. One copy ofthis document should be kept in a handylocation in the house and a second copyshould be provided to the Council forrecord purposes.

The rain garden forms an intrinsic part ofthe stormwater drainage system for the

property and has been installed as part

of an approved resource and / or buildingconsent.

In terms of North Shore City Councilsstormwater bylaw, the property owneris responsible for the continuingoperation and maintenance of theprivate stormwater system serving theirproperty.

The rain garden may not be r emoved or altered

in any way without obtaining a resource

consent and building consent from the Council.

normal rainfall events that happenthroughout the year and which wouldnot cause significantly increased runoff

in the absence of development and itsassociated impervious surfaces.

Rain gardens are basin-like, denselyplanted gardens which serve astormwater management function byfiltering stormwater slowly through avegetated soil layer into a drain locatedbeneath the soil, within a layer of freedraining stone. This is known as theunderdrain.

Rain gardens are designed to capture allthe stormwater runoff from small stormsand the initial stormwater flow fromlarger storms.

Further details of the rain graden systemare provided in the annexures.

Stormwater runoff from intense rainfallevents initially ponds in the rain gardento a maximum depth of between 150mmand 200mm and then drains slowly

through the underlying soil over aperiod of a few hours to a maximum ofone day. Sediments and their attachedcontaminants are retained by filtering.

Dissolved contaminants such as zincand copper are retained by adsorption tothe solid material in the soil. Some watervolume reduction is achieved throughevapotranspiration from the plants inthe rain garden and infiltration into thesurrounding soil. Water reaching thebase of the rain garden is interceptedby the subsoil drain which is connectedto the approved stormwater outfall forthe property; usually the Councils pipedstormwater network.

A large diameter overflow pipe or cesspitlocated about 200mm above the top ofthe rain garden allows excess rainwaterto safely drain away when the rate orquantity of rainfall exceeds the amountwhich can filter through the rain garden.This overflow is also connected to the

approved stormwater outfall for theproperty.


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4. Operation and MaintenanceRequirements

Property owners should periodicallyinspect their propertys plumbing anddrainage system for leaks and faults.Similarly the rain garden requires periodicinspection and maintenance. Mostactions are relatively simple to performand may easily be carried out by the

property owner. The following table setsout the recommended inspection andmaintenance actions for a typical raingarden. Your system may not be providedwith all of the components listed andmay have additional features not coveredbelow.

Component Recommended Actions Frequency

Soil moisturecontent

During dry periods the underdrain may cause thesoil to dry out. Plants should be watered as andwhen necessary like any normal garden. Thisis particularly important with new rain gardenswhere the planting is still establishing.

Regularlyduring dryperiods

Overflow & outletpipes

Inspect for clogging and remove any debris andrubbish. There should be no water ponding in therain garden within 12 to 24 hours after a storm.

Monthly

Weeds Inspect and remove weeds. 3 to 6 monthly

Plants Inspect, prune, thin and replace as required. 3 to 6 monthly

S ediment Inspec t r ain gar den for fine s edi ment buil d up. If a crust has formed, remove it and re-work the toplayer of soil.

3 to 6 monthly

Er osion Inspec t rain gar den for er osion caused by stronginflows. Repair as necessary.

3 to 6 monthly

Mulch Mulch suppresses weeds and retains moisture.Inspect and replace as necessary. Excess mulchmay need to be removed every few years.

Annually

Note: The maintenance frequency suggested above is the recommended minimum. After stormsadditional inspections may be warranted.

5. Contacts

Installer Name: Tel:

Company: Fax:

Address: Mobile:

A/H Tel:

Email:

Plumber Name: Tel:

Company: Fax:

Address: Mobile:

A/H Tel:

Email:

Nursery Name: Tel:

Company: Fax:

Address: Mobile:

A/H Tel:

Email:


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Notes: Notes:


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ANNEXURE 1

Rain Garden DrawingsNote: This drawing is for a typical raingarden installation. Some rain gardensmay differ from that shown.

The rain garden installer or propertyowner, as appropriate, should attach adrawing specific to the approved raingarden installation for the property.

Runoff from drivewayand paving areas

Provision forexcess overflow

Planting and mulch

Overflow outletconnected to outlet pipe

Perforated pipe(underdrain)

Outlet pipeto stormwater

outfall

Planting Soil

Gravel

Grass

Sand Bed(optional)


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ANNEXURE 2

Rain Garden Location PlanNote: The rain garden installer or propertyowner, as appropriate, should attach adrawing indicating the location of the raingarden and associated systems on theproperty. The level of detail provided shouldbe sufficient for future property owners andinspectors to locate the various componentsof the rain garden with a minimum ofinconvenience.

Example:

Brown Road

House

RainGarden

Courtyard

Driveway


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ANNEXURE 3

Proprietary ProductsOperating and ServiceInstructionsNote: The rain garden installer or propertyowner, as appropriate, should attach anyrelevant product brochures, manualsor service instructions relevant to thespecific rain garden installation on theproperty. This may, for example, includeadvice on suitable plant species for therain garden and appropriate maintenanceactions.


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Rain Garden

Need help?

For more information please contact the

ActionLine (09) 486 8600 or

www.northshorecity.govt.nz

IS WT 0000 11/07

Documents

New Zealand; Rain Garden Owner's Manual - North Shore City Council