Stormwater Flashcards
The objective of a stormwater drainage system is:
- regulate the storm surface run-off rate of flow and volume
- control groundwater levels - protect the quality of both
Remedial or mitigation works often need to be completed on stormwater drainage systems to:
ensure the agreed level of service are maintained and adverse effect on the environment are no more than minor.
What are potential adverse effects for a stormwater drainage system?
- flood damage
- surface and channel erosion and sedimentation
- water pollution
- loss of bio-diversity
- damage to aquatic ecosystems
What are some minimum levels of service for a stormwater drainage system?
- safeguard people and property
- surface water from an event shall not enter buildings
- disposal constructed to convey surface to an appropriate outfall
- flood mitigation rules
Other minimum levels of service considerations:
- future sea level rise
- climate change
- land settlement
- future development
Stormwater drainage systems require consent to discharge from
the district council and consent from the Canterbury Regional Council (Environmental Canterbury)
Discharge consent needed for both…
construction and operation
Common methods to estimate flood flows:
- rational method (Q=CIA)
- modified SCS method (auckland)
- hydrological and hydraulic models
Freeboard provides contingency against:
- flood level estimation methods
- future climate change
- system failure
Why treat stormwater?
- receiving environment protection
- public health
- recreational values
- aesthetics
What contaminants are in residential stormwater?
- metals
- nitrogen
What contaminants are in rural/bush stormwater?
- nitrogen
What contaminants are in road stormwater?
- metals
- phosphorus
- suspended solids
What contaminants are in industrial stormwater?
- metals
- phosphorus
- suspended solids
- chemicals
What is first flush?
The first third of rainfall event which has the highest concentration of contaminants. Focus treatment on first flush contaminant removal.
What are some contaminant management approaches?
- planning controls
- at source treatment
- end of pipe treatment
- community education
What is at source treatment of contaminants? + examples
Treatment on site prior to discharge to network
- “LID devices” - rain gardens, green roofs, biofiltration trenches
- Proprietary device sized for site (sand filter/ catchpit filter)
Examples of end of pipe contaminant treatment:
- wetlands, wet and dry ponds
- large proprietary device (sand filter, downstream defender)
Explain community education as a contaminant management approach.
- changes behaviour
- promotes “ownership”
- can be critical to success
Choice of contaminant treatment approach considerations:
- site constraints
- financing
- consenting authority requirements
- ongoing responsibility and maintenance
What information is needed for stormwater system design?
- site infiltration characteristics
- source of contamination
- catchment areas imp + perv
- topographical survey
- existing services
- existing drainage/ treatment
General rules of erosion and sediment control:
- minimise disturbed area
- divert clean flows around the site
- provide a buffer to watercourses
- restore disturbance asap/ cover temporarily
- minimise erosion
- prevent sediment exiting site
