Module 4 - Water Sensitive Urban Design Flashcards
What is WSUD?
Using the way we design and develop our urban
spaces to manage our effects on the water cycle, and
thereby providing better places for people to live, work
and play.
What are the key principles of Water sensitive urban design?
Key principles:
Protecting and enhancing waterways (including WQ)
Restoring the urban water balance
Conserving water resources
Integrating stormwater treatment so that it offers
multiple beneficial usesIntegrating water into the landscape
Reducing peak flows and runoff
Easy and cost effective implementation
WSUD Motivation?
The importance of our rivers, lakes and sea in our urban environments Flooding damage Erosion damage Pollution effects Rising costs under climate change Opportunities to retrofit Opportunities in new development Creating multi-functional urban areas
Barriers to implementation of WSUD
Regulatory framework barriers
Assessment and costing: Quantifying intangible benefits
Marketing and acceptance
Technology and design and complexity integrating into landscape-scale water management systems
Key components to Enabling WSUD
- Socio-political capital
- Implementation benefits from having a bridging
organisation leading it - Trusted and reliable science
- Binding targets
- Accountability for achieving the stated outcomes and dedicating to steering the process so it gets there
- Strategic funding
- Demonstration projects and training
- Market receptivity
Examples of WSUD
- Water-efficient appliances to reduce potable water use
- Greywater reuse as an alternate source of water
- Detention of stormwater
- Reuse, storage and infiltration of stormwater
- Use of vegetation for stormwater treatment purposes
- Water efficient landscaping
- Minimising the ecological footprint of water supply, wastewater and stormwater projects
- Localised wastewater treatment and reuse systems
- Provision of stormwater or other recycled urban waters to supplement ‘environmental flows’
- Flexible institutional arrangements to cope with increased uncertainty and variability in climate
- A focus on longer term planning
- Diversity of water sources
Wet pond functions
- Water quality treatment
Via sedimentation – retention time in pond allows settling to occur
Via plant action – facilitates sedimentation, biological uptake of nutrients, metals binding - Water quantity (flow) control
Peak flow attenuation - Erosion control
Factors influencing pond performance
- Inflow volume
- Inflow quality (e.g. sediment load/concentration)
- Inflow rate
- Particle size distribution
- Pond shape (e.g. length to width ratio)
- Forebay design (e.g. removal of coarser sediments; flow distribution into main pond)
- Inlet and outlet locations (e.g. short-circuiting potential)
- Pond bathymetry
- Vegetation (e.g. treatment contribution)
- Temperature
- Surface wind effects
Pond Sizing by volume regulations
Auckland: Capture 1/3rd of 24 hour duration, 50% AEP event
Christchurch: Capture volume of 2% AEP event of critical duration for receiving waterway (e.g. 36 hour event for Heathcote catchment)
NZTA: Capture 90th percentile rain event
Pond Sizing by sediment settling velocities
Sediment settling velocities can be calculated using Stoke’s Law or Weber’s Law
Design decisions: pond shape
Consider: Amenity, topography
minimum length to width ratio of 3:1 (4:1 is better)
If pond flow path is long, avoid flow fast velocities
Increased pond volume = increased performance
Rectangular shape most efficient (circular worst)
Design decisions: inlet and outlet configuration
Considerations: short-circuiting, topography
Distributing inflow across pond width enhances hydraulic efficiency
lengthen flow path by offsetting inlet and outlet locations
Consider natural flow cells created by inlet location and pond shape
Outlet using slot or orifice to control water release rate
Design decisions: baffles
baffles to lengthen flow path. check flow velocities to
ensure sediment is not resuspended
Subsurface baffles improves hydraulic efficiency significantly
Further design guidance for Wet ponds
Maximum flow velocity to avoid resuspension: 0.25 m/s during 10% AEP storm
Minimum forebay depth: 1 m to help reduce velocities
Keep side slopes shallow for safety and maintenance access
Can also use pond edges for vegetated zones
Incorporate ability to drawdown water level for maintenance
Initial locational checks for raingarden Christchurch
Check depth to seasonally high water table (October)
30 mm/hr < infiltration use underdrain
