Urban development substantially changes a landscape by replacing absorbent soil, grass, and vegetation with buildings, roadways, sidewalks, and parking lots constructed from non-absorbent materials. The upshot is that it causes major issues for engineers, environmental scientists, and urban planners who need to then figure out how to implement solutions when it comes to stormwater drainage.
Understanding Stormwater Run-Off
Prior to urbanization, stormwater is readily absorbed into the ground through a process called infiltration. However, paving over large tracts of land with impervious surfaces prevents natural infiltration. Now when it rains, water cannot soak into the ground and runs off the hardened surfaces (known as run-off), collecting pollutants before entering natural waterways or storm drainage systems.
In urban areas, stormwater run-off contributes massively to water pollution. As it travels over streets, parking lots, construction sites, and industrial zones, stormwater picks up sediment, chemicals, litter, fertilizers, oil/grease residues, and bacteria that drain directly into lakes, rivers, and oceans. It is this contaminated water run-off that causes a plethora of problems when it comes to water quality and aquatic ecosystems.
Managing Increased Volumes of Stormwater
Urbanization causes a substantial increase in the volume of stormwater an area must accommodate due to:
- Less infiltration and more run-off occurring across paved surfaces.
- Larger portions of land covered by impervious surfaces.
- Development occurring in low-lying areas and floodplains.
- Construction of efficient roadway drainage systems that consolidate stormwater from large contributing areas.
According to Global Gutter Systems, to prevent localized flooding, engineers must design stormwater infrastructure capable of conveying greater run-off volumes at faster rates compared to natural terrain. Underground storm sewer networks, open channels, detention basins, drainage gutter systems, and other measures provide collection points and transport capacity.
Slowing Down Run-Off with Green Infrastructure
While storm sewer networks efficiently drain urban landscapes, they also quickly shoot contaminated stormwater into receiving waters. Cities mitigate this by integrating “green infrastructure” systems that help to slow down, spread out, and filter run-off.
Green infrastructure uses soil, plants, porous pavements, rain gardens, green roofs, constructed wetlands, and stormwater tree trenches to mimic natural hydrology. These distributed practices capture and store stormwater, allowing it to slowly infiltrate, evaporate, or be taken up by plants and soil.
We can design green infrastructure practices into streets, parking lots, sidewalks, medians, buildings, parks, schools, municipal properties, and abandoned lots. Distributed throughout an urban area, they collectively store hundreds of thousands of gallons of water and prevent it from rushing into water bodies.
Protecting Local Waterways
Careful stormwater management protects the health of rivers, lakes, wetlands, and coastal areas located downstream from cities. Contaminated run-off entering water bodies degrades said water quality while damaging aquatic ecosystems in many ways.
Through stormwater management methods such as using green infrastructure, cities can substantially reduce the amount of pollution collectively flowing into nearby water resources during wet weather.
Coordinating Stormwater Planning
To manage urban stormwater, there needs to be coordinating planning across city departments, infrastructure agencies, parks, transit districts, utilities, and landholders. Stormwater master plans help to identify priority areas, set pollutant reduction requirements, and establish long-term budgets for capital projects, operation, and maintenance.
Cities also implement stormwater regulations on new developments. These include rules about paving/soil disturbance limits, requiring infiltration or detention systems, banning certain high-polluting activities, and controlling illegal discharges into storm drains. Local permitting, inspections, and enforcement ensure sites adhere to stormwater plans.
Going forward, stormwater systems need to withstand more intense rainfall and flooding because of climate change. Rising sea levels cause coastal flooding during storms, which damage infrastructure. Creating climate resilience means things like upgrading conveyance capacity, leveraging green infrastructure, enacting higher development standards, and improving emergency preparedness.
Expanding cities can grow sustainably with careful planning. Following stormwater management principles allows development to progress while protecting precious water resources.