Week 9: Design - Treatment Systems Pt II

Question 1

Permeable pavements are suitable for:

Answer 1

• Small to medium catchments
• Lightly trafficked area
• No sharp acceleration or turning forces
• Low sediment and contaminant areas
• Not for AEP events, secondary flow management should be provided

Suitable for carparks, driveways, street-side parking, residential

Question 2

What is PICP?

Answer 2

Permeable Interlocking Concrete Pavement

Question 3

What are the main elements of a permeable pavement device?

Answer 3

1. Overflow drainage
2. Surfacing (permeable or porous)
3. Edge restraints
4. Bedding layer
5. Basecourse (permeable)
6. Perforated underdrain
7. Basecourse enclosed with permeable geotextile
8. Optional - impermeable liner
9. Sub-grade (underlying soils)
10. Jointing material

Question 4

What are the different types of permeable pavements?

Answer 4

• Permeable pavers
• Resin locked aggregate
• Pervious concrete
• Permeable interlocking concrete pavers

Question 5

What are the different types of drainage in permeable pavements?

Answer 5

• Full infiltration
• Partial infiltration
• No infiltration

Question 6

Describe passive permeable pavement treatment.

Answer 6

No design.
- Catchment is only the pervious area
- Surrounding surfaces drain away
- Full infiltration

Question 7

Describe active permeable pavement treatment.

Answer 7

Designed system
- Pervious surface acts to collect and filter stormwater from adjacent area.
- Total catchment ratio to pervious area is 2:1 (max).

Question 8

Outline the hydrologic sizing process for permeable pavements.

Answer 8

1. Determine the hydrologic flow for retention/detention water quality volume. (90th %ile? 95th %ile?)
2. Design for detention requirement.
3. Determine retention/infiltration.
4. Underdrain layout, inflow, individual conveyance capacity, number of pipes.
5. Excess runoff

Question 9

What are some sediment and debris cleaning options?

(For permeable pavements)

Answer 9

Small paver installations:
- Top up jointing sand after 1year, every 10 years thereafter
- Regular cleaning of organic sediment. Blowing is sufficient
- General clean, moss removal with rotation head cleaner

Large paver installations:
- Top up jointing sand after 1 year, 7 years thereafter
- Once per year general clean, moss removal with rotating head cleaner
- Inspect infiltration rate every 10 years.
- Hydrovac

Question 10

What are the general benefits of green roofs?

Answer 10

• Retention for storm events
• Reductions of runoff
• Peak flow reduction
• Outflow delay
• Peak flow delay
• No further roof runoff treatment required

Question 11

What determines green roof suitability?

Answer 11

Roof type
- Ventilation (ventilated vs. unventilated)
- Insulation (insulated, double insulated, non-insulated, inverted)
These factors affect
- vapour pressure/moisture build-up
- Load capacity

Roof should also have slope
Designed for detention and retention

Question 12

What are the main elements of green roofs?

Answer 12

• Plants
• Growing medium
• Filter cloth
• Drainage layer
• Root barrier
• Waterproof membrane

Question 13

What are different types of vegetation strata?

(Growing medium in green roofs)

Answer 13

• Bulk materials
• Substrate panels
• Water storage layers
• Vegetation mats

Question 14

What are some important properties/characteristics of vegetation strata?

(In green roofs)

Answer 14

Organic matter
- Combustile/fire considerations
- Decomposition & compaction

Structural/compaction requirements
- Bulk/aggregate
- Substrate panels
- Shear reinforcement

Hydrologic
- Water holding capacity

• Permeability
• Air content

Characteristics
- pH
- Salinity
- Nutrients
- Density

Question 15

What are different types of drainage materials?

(In green roofs)

Answer 15

• Aggregates
• Recycled aggregates
• Drainage matting
• Drainage panels
• Drainage substrate panels

Question 16

What are the key drainage and substrate characteristics?

(In green roofs)

Answer 16

• pH
• Salinity
• Permeability
• PSD
• Structural and weatherability considerations

Question 17

What are some key considerations in plant selection?

(in green roofs)

Answer 17

• Lack of shade
• Roofs are often more exposed to wind
• Drought tolerant
• Low maintenance required
• Greater temperature extremes due to thin substrate
• Low organic matter and nutrient requirements
• Short depth for roots
• Evergreen
• Ground cover (as opposed to taller plants)
• Non-invasive/weed-like

Question 18

What are the key design elements of green roofs?

Answer 18

• Water collection
• Public access
• Fire safety
• Protect edges from roots and water
• Ecological diversity

Question 19

What factors determine suitable location for rain tanks?

Answer 19

• Stable flat soils, no ponding
• Hard surface (suitable for weight of full tank)
• No overhanging branches. Good maintenance access
• No tree roots
• Avoid direct sunlight (sun causes algae/microbial growth)

Question 20

What are the steps for sizing a rain tank for detention only?

Answer 20

1. Tank height
2. Average discharge rate
3. Orifice diameter

Question 21

What are the steps for sizing a rain tank for retention + detention?

Answer 21

1. Allocate runoff
2. Tank diameter and area
3. Orifice height
4. Detention storage height
5. Average discharge flow rate
6. Orifice diameter