1. A risk based framework for managing stormwater
inputs to estuaries, using ecological condition triggers
Jocelyn Dela-Cruz, Anthony Pik, Paul Wearne, Tony Weber, Peter Scanes and Tim Pritchard

2. No state wide planning policy on WSUD
Councils have set their own policies and stormwater management targets
44 Councils
13 Policies
Butler, R. (2015)

4. 6 District Plans:

5. 8 Regional Plans:

6. Lake Illawarra exceed trigger value 5.3 8.1 2.1 3.9 4.3 3.8 2.5 2.4
2.2
1.4
4.4
3.9
9.6
2.5
3.5
2.1
4.3
2.4
3.8
exceed
trigger
value
Data from WCC (2015)

7. http://www. illawarramercury. com

8. Stormwater water quality targets (Landcom)
How do we accommodate urban development while protecting the community’s values and uses of the lake?
Stormwater water quality targets (Landcom)
40-45% reduction in TN load post development
55-65% reduction in TP load post development
80-85% reductions in TSS load post development
Neutral or Beneficial Effect (NorBE)
works in theory
‘no net increase’ in practice

10. Risk-based Framework for Considering Waterway Health Outcomes in Land Use Planning Decisions
Risk Evaluation
Risk Analysis
Establish Context, and Identify Risks
Land use scenario
Risk assessment
Effects Based Assessment
Waterway
Objectives
Communication and Consultation
Monitoring and Review
Strategic Impact Assessment
Are the risks acceptable? NO
YES
Risk treatment
Land use settings
Detailed design and implementation plans

11. determine sustainable load
Effects Based Assessment
Landcom, no net increase
Catchment Model
Photos: D. Wiecek, OEH
determine sustainable load
determine impact
Hydrodynamic/Hydraulic Model
Ecological Response Model
(meeting objectives)
Littleboy et al., 2009; Proceedings of the 18th World IMACS/MODSIM Congress
Sanderson and Coade, 2010; Environmental Modelling and Software 25(6),

12. no controls no net increase Chl a (µg/L) current Landcom
trigger
SUSTAINABLE LOAD
TN (kg/y)

13. e.g. urban residential (15 dwellings/ha)
Forest
(Greenfield)
Rural
Agricultural
(Brownfield)
Re-development
(from 10 d/ha)
TN stormwater load reduction
Landcom
Net Present Value of Basin ($k/ha)

14. Landcom (improvement)
sustainable load
no net increase (runoff)
no net increase (improvement)
TN (kg/ha/y)
Greenfield
Landcom (runoff)
Landcom (improvement)
TN (kg/ha/y)
Re-development

15. Benefit Map
maintain or improve
improve
maintain

16. Infrastructure planning and offsets:
e.g. WSUD capability
high
low

17. Planning of Green-Blue Grid, co-benefits
River Styles - Recovery Potential

18. TN (kg/ha/y)
water clarity
Micro-algae
flushing

19. River Styles - Fragility Proximity
Environmental Assets
Macrophytes (EECS)
Protected wetlands
Key Fish Habitats
Shorebird Habitats

20. RISK = X LIKELIHOOD (TN per hectare, flushing, fragility, river order)
CONSEQUENCE (micro-algae, water clarity, aquatic assets)
RISK = X

21. ACTION 5.4.1 – protect sensitive estuaries and coastal lakes
This work has led to:
ACTION – protect sensitive estuaries and coastal lakes
ACTION – implement a risk-based decision framework for managing water quality and waterway health in Lake Illawarra
ACTION – implement a risk-based decision framework for managing water quality and health for all estuaries and lakes where development is planned, with priority given to sensitive estuaries and lakes

24. TAKE HOME MESSAGE
Not all waterways are the same, use an effects based assessment
Not all development scenarios are the same, waterway health improvements are more attainable under Brownfield and Re-development scenarios
Stormwater management should be commensurate with level of risk, not a one-size-fits-all approach