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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