5.10 Impacts of Urbanization, 5.13 Methods to Reduce Urban Runoff

Urbanization

Removing of vegetation to convert natural landscape to city (urban)

Cons of Urbanization

Replaces soil, vegetation, wetlands with impervious surfaces (concrete, asphalt, cement) which don’t allow water to infiltrate into the ground, CO2 emissions (cement production, construction machinery, deforestation, landfills needed)

What does population growth in coast cities lead to

Salt water intrusion

What causes salt water intrusion

Excessive groundwater withdrawal and sea level rise

Excessive groundwater withdrawal

Near coast, lowering water table pressure, allowing saltwater to seep into groundwater

Sea level rise

Due to warming of ocean (thermal expansion) and melting of ice caps (increasing ocean volume) can contaminate fresh groundwater with salt

Trends in population

People move from rural to urban areas for jobs, entertainment, cultural attractions causing urban areas to be more densely population, minimizing driving distance and land use

What population has the highest growth currently?

Suburban population

What’s the overall trend in the US and other nations

Movement away from less dense rural (country) areas and towards more urban (city) areas

Suburbs

Less dense areas surrounding urban areas (Lake Forest, Irvine)

Urban Sprawl

Population movement out of dense, urban centers to less dense suburban areas surrounding the city

What causes urban sprawl

Cheaper property in suburbs than in cities (larger homes for same price), easier commutes to work entertainment and cultural attractions, domino effect, fewer residents in cities lead to declin in tax revenue (fewer city services), residents leave and businesses follow, abandoned homes + businesses create blight so more people leave, expanded highway system (car transportation is easier), inc. in driving increases tax revenue (more highways), highways make it easier to community from suburbs into urban areas

Blight

Unsightly, rundown infrastructure

Environment Impacts of Urban Sprawl

Heat Islands and Urban Runoff

Heat islands

A lack of tree coverage, inc energy consumption, more reflective surfaces, allowing saltwater to lead to increases temps. In urban areas

Urban runoff

Use of impermeable spaces create 5x more runoff than a woodland area of the same size; reduce infiltration

Environmental consequences of urban runoff

Decrease infiltration (groundwater recharge) and rain washes pollutants into storm drawings & into local surface waters

Pollutants and effects

Salt (plant and insect death), sediment (turbidity), fertilizer (eutrophication), pesticides (kill non target species), oil and gasoline (suffocate fish/kill aq. Insects)

Solutions to reduce urban runoff

Permeable pavement, rain garden, public transit, compact buildings

Permeable pavement

Designed to allow storm water to infiltrate and recharge ground water

Pros of Permeable pavement

Decreases runoff, dec. pollutants carried into storm drains and into local surface water, dec. likelihood of flooding during heavy rainfall

Cons of Permeable pavement

More costly than traditional pavement

Pros of Rain Garden

Dec. runoff by allowing it to soak into garden soil surrounding storm drain, Dec. likelihood of flooding during heavy rainfall, creates habitat for pollinators, sense of place and stores CO2

Public transit

Creating more public transit (trains, buses) to Dec. the amount of car lanes on the streets, more cars = more pollutants to runoff into storm drains and local waters (motor oil, gasoline, tire pieces, antifreeze), more cars = more lands and parking lots (impervious surfaces) and more storm water runoff, public transit Dec. urban runoff, pollutants on road, CO2 emission and traffic

Building up, not out (Compact cities)

Building vertically Dec. impervious surfaces, can be combined with green roof or rooftop gardens, green roof also equesters CO2 and filters air pollutants

SMART Growth Designs

Smart Growth (Compact cities) is urban planning that focuses on improved walk ability and mass transit options to avoid urban sprawl