Stormwater

Question 1

What are the topics of stormwater?

Answer 1

• Consent to discharge
• LOS
• Flood mitigation/drainage
• Stormwater treatment
• Erosion and sediment control

Question 2

What is the objective of stormwater drainage systems?

Answer 2

To regulate surface runoff rate of flow and volume.
Control ground water levels.
Effects on environ are no more than minor.

Question 3

What are the potential adverse effects of stormwater?

Answer 3

• Flood damage
• Surface and channel erosion and sedimentation
• Water pollution
• Loss of biodiversity
• Damage to aquatic ecosystems.

Question 4

What are the minimum level of services? (building act)

Answer 4

• Safeguard property
• Surface water has 2% prob of entering building from event
• Sufficient drainage (no blockages etc)

Question 5

Minimum level of services relating to flood mitigation?

Answer 5

• Min 0.5 freeboard above the 50 - 100 year return period for predicted flood level for all habitable floors
• Defined secondary overload flowpaths
• Pip network designed for 5 - 10 year return period flood.

Question 6

Considerations for minimum level of service?

Answer 6

• Future sea level rise
• Climate change
• Land settlement
• Future dev

Question 7

Do you need a consent to discharge water?

Answer 7

Yes

Question 8

What methods are used to estimate flood flows?

Answer 8

• Rational Method
• Modified SCS method
• Hydrological and hydraulic models

Question 9

What is a freeboard?

Answer 9

Distance between flood level and floor of structure.

Question 10

What is the rational method?

Answer 10

Empirical procedure for determining runoff from small catchments.
Q = CIA

Question 11

Why treat stormwater?

Answer 11

• Public health
• Environmental protection
• Recreational values (fisheries)
• Aesthetics

Question 12

What have a first flush?

Answer 12

The first third contains the highest conc of contamination.

Question 13

That are the four things in the contaminant treatment train?

Answer 13

Planning controls
At-source treatment
End of pipe treatment
Community education

Question 14

What are examples of at source treatment methods?

Answer 14

Rain gardens, green roofs, bio-filtration trenches.
Sand filter, catchpit filter.
Rain watertanks, minimal impervious area, soakage.

Question 15

What are examples of end o pipe treatment methods?

Answer 15

Wetlands, wet and dry ponds.

Sandfilter, downstream defender.

Question 16

What are examples of community education?

Answer 16

Signs.

Done by changing behaviour, promotes ownership.

Question 17

Whats bad about soils being very pervious?

Answer 17

Not good for treatment, that is why soakage devices are good because they retain the water, treat it and discharge it.

Question 18

How do you choose an appropriate approach?

Answer 18

• Site constraints
• Finance
• Consents
• Maintenance and responsibility

Question 19

What information is needed when designing a system?

Answer 19

• Infiltration (not > 75 mm/hr)
• Source of contam
• Catchment area
• Topo survey
• Current services
• Current drainage/treatment.

Question 20

What are the general rules for erosion and sediment control?

Answer 20

• Minimise disturbed area
• Divert clean flows around site
• Buffers to watercourses
• Restore asap (cover temp)
• Minimise erosion (drains etc)