Stormwater harvesting in urban environments Overview of engineering practice

1Results through Experience

Definitions

• Urban stormwater - “net increase in run off and decrease in groundwater recharge resulting from the introduction of impervious surfaces such as roofs and roads within urban development”

• “Urban stormwater” is only available within the urban growth boundary

• Base/dry weather flows in drains & waterways are not considered urban stormwater - no access to base flows will be permitted

2Results through Experience

Current allocation rules for stormwater harvesting

(DSE Sustainable Water Strategy – 2006)• If stormwater is flowing to the sea via a drain, 100% of the

stormwater may be harvested

• If stormwater is flowing to a stream from an existing development up to 50% of existing stormwater can be harvested for use and 50% is reserved for the environment

• If there is a scheme to harvest more than 50% of the resource a study is required to assess implications for the environment

• All stormwater generated from new development is available for harvesting with the aim of the development having no nett impact

3Results through Experience

Who Administers Stormwater Assets?

4

Harvest Source Legislation Responsibility Melbourne Water drain, waterway or waterbody

Section 51, Water Act 1989 Melbourne Water

Council drain for domestic use – single property

Not applicable Council approval only

Council drain for multi- residential or commercial use

Not applicable Council approval only

Council wetland, lake or waterbody for other than domestic use (not supplied by roof runoff)

Section 51, Water Act 1989 Melbourne Water Council approval required

Private drain within private property Not applicable No licence required Roof Runoff Exempt from licensing

requirements Council approval may be required.

The harvesting of water from Melbourne Water’s drains and waterways requires a licence under Section 51 of the Water Act 1989.

Results through Experience

Australian Rainfall

Australian rainfall is low, seasonal and highly variable compared with other continents such as Europe and North America

5Results through Experience

Rainfall patterns

6Results through Experience

Annual rainfall Melbourne

7

Annual Rainfall

300

400

500

600

700

800

900

1000

1855 1865 1875 1885 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005

Year

Rai

nfa

ll (

mm

)

Results through Experience

Rainfall – monthly distribution

8

Low Scenario 1

0

20

40

60

80

100

120

Jan Feb March April May June July Aug Sep Oct Nov Dec

Rai

nfa

ll (

mm

)

1879

1945

2003

1940

1926

1986

1915

1968

1944

1862

1933

Low Scenario 1

Low Scenario 1 covers 38% of years within this range (11/29).

Results through Experience

Typical irrigation demands (Melbourne)

9

0

5

10

15

20

25

30

35

40

45

50

January

Febru

ary

Marc

h

April

May

June

July

August

Septe

mber

Octo

ber

Novem

ber

Decem

ber

ML

Results through Experience

Some thoughts..• Rainfall is cyclical meaning there are peaks and

troughs• The demand for water could also be cyclical e.g.

irrigation• Distribution of “peaks and troughs” in a year can

be more important than the total annual rainfall• Statistical Average Rainfall data can be

misleading • Selection of the rainfall years for further

modelling is a risk – based exercise10Results through Experience

Stormwater Harvesting Scheme Major Components

11Results through Experience

12Results through Experience

Diversion of flows

13Results through Experience

Diversion Structures•divert the pre-determined range of flows for harvesting •while allowing flows outside of this range (larger/by-pass flows and smaller base/environmental flows) to continue via the designated conveyance system

These functions could be delivered by various controlling mechanisms generally falling into the two major categories…

14Results through Experience

15

Flow Diversionsi) Transverse weirii)Side weiriii)Drop structure

Flow Controli) Throttle pipeii) Adjustable Penstockiii) Hydrobrake or similar proprietary deviceiv) Orifice plate/Sutro weir

Results through Experience

Treatment for reuse - Stormwater

16Results through Experience

National Guidelines

17Results through Experience

State guidelines

18Results through Experience

Overview of Treatment Requirements - Stormwater

• Small to medium schemes• No supply to third parties• Unrestricted spray irrigation• Requirements are to achieve:

Disinfection to achieve >2.5 log reduction in viruses, parasites and bacteria

EC < 10 CFU/100 mL Turbidity 10 – 25 NTU

(subject to satisfying disinfection requirements)

http://www.ephc.gov.au/ephc/water_recycling.html

19Results through Experience

20

Storages

Above ground

Underground

21Results through Experience

Example one – for those who love bright colour…

22Results through Experience

and for those who are more traditional with colour…

23Results through Experience

and for those who use concrete and concrete only

24Results through Experience

and the above ground tanks…

25Results through Experience

Distribution system

26Results through Experience

Distribution Pipe Work

• Colour coded pipes (lilac)• Removable handles for hose taps• Signage e.g. “Recycled Water –

Do Not Drink”• Allow flush valves for periodic

flushing of the system

27Results through Experience

Definition of Volumes

28

Volume diverted

Volume collected

Volume utilized

Results through Experience

Operation & Management of Stormwater Harvesting Schemes

29Results through Experience

O&M itemized

• Catchment management• Incident response (oil spillage, pumps failure

etc)• OH&S (e.g. confined space entry

requirements)• Regular inspections• Maintenance of equipment (cleaning)• Monitoring

30Results through Experience

ACKNOWLEDGEMENTSIn preparation of this presentation the author

would like to acknowledge the support and contribution from the following professionals:

•Steve Hosking, Melbourne Water Corporation•Water & Carbon Group•Daryl Stevens, Atura Pty Ltd•Murray Powell, Optimal Stormwater Pty Ltd

Results through Experience31

QUESTIONS TIME…32Results through Experience

THANK YOUResults through Experience