Our built environments, including infrastructure and man-made elements, along with the residents of it are interconnected with the natural ecological systems that occupy the same spaces. A demographic shift is occurring as a growing proportion of the population moves into urban areas (McDonald, 2008). Close to 80% of the US population currently resides in urbanized areas (Pickett, Cadenasso, Grove, Boone, Groffman, Irwin, Kaushal, Marshall, McGrath, Nilon, Pouyat, Szlavecz, Troy, Warren, 2011), it is important to study urban environments and the ecological footprint they entail. Few, if any, ecological systems still remain unscathed by anthropogenic influences (Palmer, 2004). Future ecological perspectives must recognize humans as a major influence/factor within functioning ecological systems that still manage to meet the needs of those that exist within them. A city that is meeting the environmental goals of sustainable development is a city that meets the environmental requirements of those that inhabit it, while still reducing environmental costs (McGranahan & Satterthwaite, 2002). Urbanization has the following effect on the surrounding hydrologic cycle:

Urbanizations’ Altercations of The Hydrologic Cycle:

• Increase impervious surfaces
• Connectivity of storm drains and impervious surfaces
• Connectivity of storm drains and impervious surfaces
• Stormwater volume & velocity
• Waste Energy &Waste Matter
• Municipal &Industrial Discharge
• Nutrients, Metals, Pesticides, Oil, & other Contaminants

Hydrologic Response From Urbanization:

• Hydrology - Increase in erosive flow, volume, velocity, peak flow, decrease in time to peak flow
• Water Chemistry - Increase in Nutrients (N+P), Toxicants, Temp
• Channel Morphology - Increase in channel Width, Depth, Decrease in complexity
• Organic Matter - Decrease in retention (related to decrease in nutrient uptake)
• Fish/Invertebrates -Decrease in sensitive fishes and invertebrates, Increase in tolerant species
• Algae - Increase Eutrophic Diatoms, Decrease in Oligotrophic Diatoms

Where do we go from here?

Increasing permeable surfaces and naturally functioning retention areas are a functional solution to the hydrologic responses above.  These examples are both feasible and functional in many scenarios.

Bioretention Benefits

Bio retention of water prior to its release into native soil or the current existing storm water management allows for a reduction in many of the hydrologic stressors listed above. The intended goal of a bio-retention area is to reduce run-off volume and aide in nutrient reduction (via nutrient retainment/uptake). As stated by the Virginia Water Resources Research Center, “Bioretention creates a good environment for runoff reduction, filtration, biological uptake, and microbial activity, and provides high pollutant removal. Bioretention can become an attractive landscaping feature with high amenity value and community acceptance.” Bio-retention pits are a feasible, green solution that can help produce a natural functioning hydrologic cycle within man-made environments.

A few considerations/limitations:

• Water table: Bio-retention pits should always be separated from the ground water prevent intersection with the filter bed.
• Site topography: ideal slope remains between 1 and 5 %
• Space availability: this an adaptive characteristic. Typically the bio-retention surface area is between 3 and 6% of the drainage area.
• Utilities: above and below ground. Vegetation, digging, and drainage considerations.

(from Virginia Water Resources Research Center)

Permeable Concrete/Pavement Benefits

Permeable pavements all offer a reduction in stormwater peak flows, total volume and pollutant concentrations (EPA). In addition, permeable pavement slows the filtration process of stormwater, which allows for sedimentation to occur. As much as 80 percent total suspended solids reductions have been achieved using permeable pavement (EPA). Leadership in Energy and Environmental Design (LEED) and Green Globes offer credits for projects capable of achieving such high standards (EPA). Because permeable pavements provide more traction than many typical pavement surfaces(rougher surface), they offer increased pedestrian and vehicle safety, making them especially attractive for municipal green infrastructure and low impact development projects (EPA).

Key Siting and Maintenance Issues With Pervious Concrete:

• Load bearing roads need to have special considerations
• Do not install in areas where hazardous materials are loaded, unloaded, or stored.
• Avoid high sediment loading
• Divert runoff from disturbed areas until stabilized
• Do not use sand for snow or ice treatment.
• Periodic maintenance to remove fine sediments from paver surface

(EPA)

Sources:

McDonald, R. (2008) Global urbanization: can ecologists identify a sustainable way forward? The Ecological Society of America. 99-104.

Nechyba, Thomas J. and Walsh, Randle P. “Urban Sprawl”, The Journal of Economic Perspectives , Vol. 18, No. 4 (Autumn, 2004), pp. 177-200

McGranahan and Satterthwaite, “The Environmental Dimensions of Sustainable Development for Cities”, Geography, 2002.

“EPA - Stormwater Menu of BMPs.” U.S. EPA ColdFusion Server. N.p., n.d. Web. 6 Apr. 2013. Stable URL: http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=browse&Rbutton=detail&bmp=135

“BIORETENTION.” Virginia Water Resources Research Center | Virginia Tech . N.p., n.d. Web. 6 Apr. 2013. Stable URL: http://vwrrc.vt.edu/swc/NonPBMPSpecsMarch11/VASWMBMPSpec9BIORETENTION.html

“USGBC-LI Blog.” USGBC-LI Blog. N.p., n.d. Web. 5 Apr. 2013. Stable URL: http://usgbc-li.blogspot.com

SEALE, SHELLEY. “Urban Patchwork | Growing food and community in the city. | Austin, TX.” Urban Patchwork | Growing food and community in the city. | Austin, TX. N.p., n.d. Web. 5 Apr. 2013. Stable URL: http://Urbanpatchwork.org

Pickett STA, Cadenasso ML, Grove JM, Boone CG, Groffman PM, Irwin E, Kaushal SS, Marshall V, McGrath BP, Nilon CH, Pouyat RV, Szlavecz K, Troy A, Warren P. (2011). Urban ecological systems: Scientific foundations and a decade of progress. Journal of Environmental Management. 92, 331-362

Palmer et. al. (May, 2004) Ecology for a Crowded Plant, Vol. 304, pp. 1251-1252