Two kinds of flooding
Flooding in a river city can come from different sources, and the remedies differ. One kind is stormwater flooding, when heavy rain falls faster than drains, sewers and soil can take it away. Water collects in streets, basements and low spots. The other kind is tidal or river flooding, when water from the river, the tide or a storm surge moves onto land.
Green infrastructure is aimed mainly at the first kind. It can help with rainfall, but it is not a barrier against high water from a river, and planners usually treat the two problems with separate tools. The background on tidal rivers and low-lying land is explained in the article on the tidal floodplain.
What green infrastructure means
In stormwater management, green infrastructure refers to practices that use soil, plants and natural processes to absorb, slow, store and clean rainwater near where it falls. This is in contrast to “gray” infrastructure, such as pipes, pumps and tanks, which collect water and move it away.
The two work together. Green measures do not replace pipes, but they can reduce the volume and speed of water reaching the pipes, which may lessen the burden on the system during moderate storms.
Why it matters in older cities
In built-up areas, much of the ground is covered by roofs, pavement and compacted soil that rain cannot soak into. Rain runs off quickly into storm drains. Many older cities, including parts of Camden according to public information about regional sewer systems, are served by combined sewers that carry both stormwater and wastewater in the same pipe. In heavy rain these systems can reach capacity and release a mixture of stormwater and untreated sewage to nearby waterways at designated outfall points. Reducing the amount of rain entering the system is one way to ease this problem. The broader topic of river health is covered under water quality, and the particulars of any local system should be checked with the responsible utility.
Common tools
Rain gardens and bioswales. A rain garden is a shallow planted depression that collects runoff from a roof or pavement and lets it soak into the ground. A bioswale is a longer, channel-like version, often placed along a street or parking lot. They use plants and engineered soil to slow water and filter some pollutants.
Street trees and tree pits. Trees intercept some rainfall on their leaves and take up water through their roots. Trees planted in larger, well-designed soil volumes can absorb more runoff and tend to live longer than trees in cramped sidewalk cutouts. Trees also provide shade, which can reduce heat on hot days, although the amount of benefit depends on species, size and location.
Permeable pavement. Surfaces such as porous asphalt, pervious concrete or open-jointed pavers allow water to pass through to a stone layer below. They are used in parking areas, alleys and low-traffic streets. They need periodic maintenance to prevent clogging, and they are not suitable everywhere.
Green roofs. A layer of growing medium and plants on a roof absorbs some rainfall and slows runoff. They add weight and cost and require maintenance.
Rain barrels and cisterns. These store roof water for later use, such as watering plants, and reduce immediate runoff.
Downspout disconnection. Redirecting roof drains from the sewer to a lawn or garden can be a simple way to keep water out of pipes, where conditions allow.
Restored wetlands and shorelines. Along tidal rivers, marshes and vegetated edges can buffer wave energy and absorb some water. Their effectiveness depends on size, location and the severity of the event.
What these tools can and cannot do
Green infrastructure is useful, but expectations should be realistic.
- It is generally most effective for frequent, smaller storms and less so for extreme downpours that overwhelm any system.
- Performance depends on soil type, groundwater levels and design. In areas with high water tables or clay soils, infiltration is limited.
- If the site has contaminated soil, designers usually avoid designs that push water through it. This is a particular consideration on former industrial land, as discussed in the article on brownfield redevelopment.
- Maintenance matters. Plants die, inlets clog and trash accumulates. A project without a maintenance plan and a responsible party often declines.
- It does not stop river or tidal flooding. Other measures, including elevation of buildings, flood barriers, drainage upgrades, pump stations and land-use rules in flood-prone areas, address those risks.
Resilience as a broader concept
Flood resilience means reducing the harm from flooding and recovering quickly when it occurs. It involves more than structures. Elements can include:
- Mapping flood risk and sharing that information with residents.
- Rules for building in flood-prone areas, such as elevation requirements.
- Protecting critical facilities such as power and water systems.
- Emergency alerts and evacuation planning.
- Support for residents who have limited resources to prepare or repair.
Flood insurance and floodplain mapping are handled through federal and state programs, and property owners should consult official sources for their own situation. Climate projections generally point toward higher sea levels and more intense rainfall events in the region, though estimates vary, so planners often build in margins of uncertainty.
Benefits beyond water
Planners often favor green infrastructure partly because it can deliver other benefits at the same time. Vegetation can improve the look of a street, create habitat, shade sidewalks and make blocks more pleasant to walk. It can also offer a use for vacant land. Some cities pair stormwater measures with parks and public space, so a single site serves recreation and drainage. Whether these side benefits are realized depends on design and upkeep.
There are also concerns. Greener, improved areas can become more expensive to live in, a pattern some call green gentrification. Residents may also worry about standing water, pests or maintenance costs. Early conversation with neighbors helps, as described in the article on community participation.
Finding current information
Stormwater rules, grant programs and local projects change. Residents can check with the municipal public works office, the local sewer authority and the state environmental agency for current plans, maps and assistance. This article is a general explanation, not engineering advice or a flood-risk assessment for any property.