Stormwater Flashcards
1
Q
Design Objectives
A
- to regulate the storm surface run-off rate of flow and volume and to control groundwater levels and protect the quality of both
2
Q
Potential adverse effects of stormwater
A
- flood damage
- surface and channel erosion and sedimentation
- water pollution
- loss of bio-diversity
- damage to aquatic eco-systems
3
Q
Building Act Requirements
A
- safeguard people and property
- surface water from an event having a 2% probability shall not enter buildings
- drainage systems for the disposal of stormwater shall be constructed to convey surface to an appropriate outfall, avoid blockages, avoid damages
4
Q
Common rules relating to flood mitigation
A
- minimum 0.5m freeboard above the X year return period predicted flood level for all inhabitable floors
- defined secondary overland flowpaths
- pipe network must be designed for the Y year return period flood.
5
Q
Considerations
A
- future sea level rise
- climate change (higher intensity storm events rain)
- land settlement
- future development
6
Q
Acceptable Overland Flow Paths
A
- roads
- parks/reserves
- avoid private properties if possible (easily blocked)
7
Q
How to estimate flood flows
A
- Rational Method (Q = CIA commonly used)
- Auckland - Modified SCS method
- Hydrological and Hydraulic models
8
Q
Freeboard
A
provides contingency against:
- flood level estimation methods
- future climate change
- system failure (e.g. blockage)
9
Q
Why treat stormwater?
A
- protection of receiving environment
- public health
- recreational values (e.g. fisheries)
- aesthetics
10
Q
First Flush
A
- highest concentration in first third of rainfall event
- focus treatment on first flush contaminant removal
11
Q
Contaminant Management Approaches
A
- planning controls
- at-source treatment
- end of pipe treatment
- community education
12
Q
At-source treatment
A
treatment on site prior to discharge to network Controls: swales, green roof - minimise impervious area - rain water tanks - soakage
13
Q
End of Pipe
A
one device serves whole catchment
- wetlands, wet and dry ponds
- large proprietary device (e.g. sandfilter, downstream defender)
14
Q
Community Education
A
- changes behaviour
- promotes “ownership”
- can be critical to success
15
Q
Canterbury conditions
A
- soils can be very pervious
- good for discharge but not for treatment
- soakage devices can combine attenuation, treatment and discharge
