Urban Water Management

Linear systems -> use once and discharge

Drinking water used for all purposes

Inflexible Systems (centralized designs)

Stromwater viewed as waste (not as a resource)

Regulations are sometimes inflexible

Hydrology

• Decrease in perviousness -> reduced infiltration -> increased surface run-off

• “Imperviousness” can be used as a predictor of the urban impact on streams

• Reduced lag time -> floods peak more rapidly

• Higher peak discharges

• Strongly reduced groundwater recharge

Morphology, habitat and aquatic life

• Streamed down cutting or streambank widening

• Channel erosion sediment budget (up)

• Poor instream habitat quality, high water temperatures

Urbanization alters flow regimes by introducing impervious surface to watersheds and influencing hydrologic and metabolic regimes

Changes in hydrologic regimes require adaptions of channel morphology (peak flow vs. base flow)

Urban waters take on large amoount of pollutions from a variety of sources (indistrial discharges, wastewater, stormwater runoff, mobile sources)

However:

• Urban water are increasingly used to improve attractiveness of newly developes cities

• Urban water can provide numerouse positive side effects

Flooding

Water scarcity

Urbanization

Aging Infrastructuree

Competing water uses

Population grwoth

Considering the entire water cycle as one system -> closing the “water loop”

Providing water fit for purposes -> industry, non-potable water

Assessing a portfolio of water sources -> stromwater, greywater

Maximize the benefits from wastewater -> employing innovative technologies to reclaim water, energy, biogas and nutrients

Considering the urban water cycle is closely linked to the watershed -> adaptive mechanisms to climate change (e.g. flood management, drought fighting)

Recognizing the importance and impacts of urban planning

Working conditions in a natural system -> no urbanization

General water mass balance

• Inflow - Outflow = Storage

  • Inflows: Precipitation, groundwater flowing into the catchment area

  • Outflows: evapotranspiration, runoff and grounwater flow exiting the area

• Precipitation - Runoff - Groundwater Recharge - Evapotranspiration = Storage

Conventional devolpment results in

Water sensitve devlopment aims to enhance infiltration, evapotranspiration and capturing and reuse of stormwater in the urban environment

Several terms have been implemented in the last few decades

• Low impact development

• Sustainable (urban) drainage systems

• Water sensitive (design) cities

• Green infrastructures

• Blue - Green Infrastructure

• Sponge City

• …

-> In General the concepts is to “restore” a city’s capacity to absorb, infiltrate, store, purify, drain and manage rainwater and “regulating” the water cycle as much as possible to mimic the natural hydrological cycle

Infiltration

Evapotranspiration

Delayed discharge

Rainwater harvesting

Combinations

Treatment

Runoff Reduction, Reduce Heating/ Cooling Costs

• Rainwater stored in a lightweight engineered soil medium

• Hardy, drought-resistance vegetation

• Reduce runoff by 50 %

• Reduce impervious area

• Reduce “heat island” effect, improve air quality

Evapotranspiration and Infiltration

• The exact amount of rainfal storage (and runoff reduction) will depend upon the depth and porosity of the planting bed

Long dip, usually along road, acts as a channel for stormwater

Prevents water from flowing down impervious surfaces

Vegetation slows water down and filters out toxins?

Conveyance, Treatment, Infiltration

• Roadside swales

• Parking lots

• Low-angle slopes only

• Opportunity for snow storage

Provides storage prior to treatment

Physical adhesion of contaminants within soils (suspended solids)

Evapotranspiration (Root uptake and evaporation)

Biological consumption of organics and pathogens

can involve infiltration or sub-drain connection dependant on soil and other sub-surface conditions

Increased routine time

Treatment, Infiltration

• Parking lot island

• Rain gardens

• Median stripes

Runoff reduction and Water Conservation

• Collect rainwater

• Downspouts directed to tanks or barrels

• Landscaping, car washing, other non-potable uses

Infiltration scenario: increase of Groundwater recharge from 10mm/a to 200 mm/a

Green roof scenario: Increase of Evapotranspiration from 100 mm/a to 300mm/a

Roof runoff quality (20% of urban areas)

Roof runoff suspended solids concentration varies from 3-23 mg/l. For an annual roof of 4800 m3/(ha*a) a load varies between 14 and 110 kg /(ha*a)

Pollutants of concern are dissolved substances (biocides and heavy metals) washed out from roof materials

Street runoff quality (30% of urban areas)

Contributes to solids pollution in urban settings with loads up to 1000 kg/ha*a with traffic as the main source

mixed areas

The loads discharged into the surface water may give and indication for the development of thresholds values in quality standards

An average concentration of 50 mg/l result in an annual area specific load of 240 kg/ha*a

1. The fine fraction (clay + silt) heavily loaded and difficult to remove

2. The coarse mineral fraction (sand + gravel), always low or unloaded and very easy to remove

3. The coarse organic fraction (vegetation waste), significantly loaded and difficult to remove

Sedimentation: settling solid contaminats by reducing the flow velocity (quality)

Filtration: physical straining of course solid contaminats through surface vegetation, adhesion to soil or filtration medium particles (quality)

Microbial breakdown of pathogenes and organics (quality)

Load reduction through evapotranspiration or infiltration. Effective results on widest range of stormwater contaminants (quanity, quality?)

Solutions for centralized and de-centralized application available

Analysis, understanding and modelling processes and fluxes at urban water interface at various spatial scales

Understanding behavior and need of urban waters

Natural (physical) and technical system components need to be analyzed

Challenges related to the scales and dynamics of processes need to be addressed

Clear problem/ task definition

Involvement of all stakeholders with interests in urban water flows and water bodies

Development of integrated system models to provide best possible representation of system’s behavior and as a communication tool