Blue Green Infrastrucutre

• as response to cholera - “the great stink”

• either combines sewer system orseparate sewer system

• but also negative aspects:

  • changes in hydrological cycle: higher surface runoff, less infiltration, less transpiration

  • changes in groundwater and surface water levels

  • urban heat island effects

  • downstream flooding risk

  • decrease of water quality (pollutants, visual quality, thermal pollution(algal blooms)

planned network of natural and semi-natural areas that utilise natural processes to improve water quality and manage water quantitiy

two types:

1. natural water features: ponds, rivers, lakes, wetlands

2. man-made features: greend buildings, streets and places -> compromisind a number of individual components: green buildings, streets and spaces

• Riparian buffer: zone close to lake or river, biological filter, hold large amounts of water, reduce erosion, increase wildlife diversity

• swales: open conveyance channles -> slow down runoff (enable sediments and pollutants to settle), reduce peak flow and give pretreatment

• bioretention basins: detain and treat stormwater -> temporarily store stormwater, runoff is filtered through vegetation and later released at controlled rate

• green roofs:

  • Pro: treat stormwater through bioretention, reduce annual stormwater runoff by 50-60%, capture 85% of some nutirent pollutants, filter air pollutans, reduce heat island effects (up to 60°C)

  • Con: energy-intensive, source of pollutants, carbon footprint from construction

• Combined: storm- and wastewater in one pipe network; all water is treated as wastewater before being discharegd into water body

  • Pro:

    • only one network

    • stormwater, which also carries pollutants gets treated

  • Con:

    • pipes can get extremely large

    • stormwater overflow releases untreates wastewater into water bodies

    • wastewater treatment plant clens “clean stormwater” -> high energy costs

• Seperate: seperate network, wastewater egts treatment, stormwater is directly released into water body

  • Pro:

    • no sewage overflow

    • less water for wastewater treatment plant

  • Con:

    • twice the network length

    • stormwater gets no treatment

    • water saving leading to low flow and odour and corrosion of pipes

• disconecting downspouts of buildings from sewer system —> redirection of water towards permeable areas, rain barrels or cicsterns

• rain barrels hold up to 150-200l (suited for single family house with garden)

• cicsterns hold up to 1000-3500l (suited for large buildings)

• reduced flood risk

• pollutant reduction

• waterway quality

• enhanced water conservation

• increased groundwater recharge (increased base flow)

• reduces heat island effect

• improved habitats (providing parks, urban forests, wetlands and vegetated swales)

• carbon sequestration

• encourage physical activity, improving (mental) health, promote social interaction

• healthier air

• provide space for partial self-sustaining life style

• multiple stakeholders

• more space is needed than grey infrastrucutre needs -> higher cost

• diffiyult to quantify benefits

• many BGI approaches require long time to reach full benefit

• initial high costs

• higher risk due to lack of experience

• Who should pay? benefactors hard to spread over multiple grous, administrative boundaries and jurisdictions

• Lock-in of traditional practices (“Why change what we have?”)

• unfamilarity with multifunctional space

• poor maintenance (insufficient resources and skilled workers)

• well suited for small rain events but large storms will overwhelm BGI