We’ve discussed how excessive runoff can present major hazards to human lives, public health, infrastructure, as well as both local and distant ecosystems. So, this prompts the question of how communities can respond to protect themselves and both the local and downstream environments. It turns out that there are a variety of techniques employed on different scales, ranging from individual homeowners to large urban planning commissions. Of course, one of the first ways to address the problem is to reduce the runoff that must be actively managed.
When left to its own devices, nature manages rainfall and snowmelt by allowing it to be absorbed into the ground, eventually recharging underground aquifers. In undisturbed areas, a healthy, balanced ecosystem can absorb and safely consume excess nutrients. Traveling among trees and over vegetated areas, runoff is slowed, and erosion is minimized. Even heavy amounts of precipitation can be reduced, and damage is minimized.
One clear strategy to managing runoff is to follow and reestablish natural processes, starting with reducing the enormous overload that quickly overwhelms manmade systems.
Rainwater Harvesting
Both businesses and individual homeowners can help reduce stormwater runoff by establishing rainwater harvesting practices on their structures. Water captured directly from rooftops is substantially less polluted than water that’s been mixed from many different sources, and it can be used for any type of graywater purpose. Washing cars and pets, watering gardens, flushing toilets, fire protection, and decorative fountains are all needs that can be supplied with untreated rainwater. Rainwater that’s been appropriately treated on-site can be used for cooking, bathing, laundry, and even drinking.
The advantages of rainwater harvesting include not only reducing stormwater load on existing infrastructure, but it can ease the strain on municipal services that struggle to keep up with the demand for treating stormwater.
Permeable Pavement
Cities and developed areas suffer from an infrastructure that limits the amount of open, undisturbed ground that would normally absorb incoming precipitation. Impermeable pavement, roads, sidewalks, and buildings all prevent water from reaching the soil and contribute to massive amounts of stormwater flowing together. Many cities are experimenting now with installing permeable paving, which are designed to allow water to move through the paving and be absorbed by the soil beneath. Sidewalks, plazas, parking lots, driveways, and low-traffic roads like residential streets are all well-suited for permeable pavement.
The principle of permeable pavement is that stormwater is diverted through small voids in the pavement surface and then filtered through an underlying reservoir filled with aggregate. After basic filtration, the slowed water is allowed to be absorbed by the underlying soil. In cases where the subsoil is not suitable for infiltration, such as heavy clay, the system can be designed to detain and gradually release the water to an alternate conveyance system.
As technology for green infrastructure and climate sensitive urban design improve, options like permeable pavement for heavily trafficked roads are becoming feasible.
Encouraging Natural Areas
Trees, shrubs, ornamental and turf grasses all demand water for survival. Soil that is covered with plant life is more absorbent and less vulnerable to erosion stemming from stormwater runoff. Natural areas in urban environments offer many other benefits, such as recreational opportunities for residents, relaxing and appealing visual elements, and certain hidden benefits like temperature stabilization and pollution reduction. Establishing and maintaining parklands scattered throughout urban developments not only help city planners reduce stormwater runoff but help make the city environment much more appealing for businesses and residents alike.
Carefully designed natural areas within urban settings also provide habitat for many species of wildlife, from pollinator species like bees and butterflies, to turtles, ducks, fish, squirrels, bats, chipmunks, and potentially hundreds of songbirds. Natural areas can provide important stopovers for many migratory birds whose traditional routes may have been threatened or eliminated altogether by encroaching development. Besides helping minimize damage from powerful storms, new and established parklands can offer a literal lifeline to our wild friends.
Wetlands
Wetland areas, which include swamps, marshes, estuaries, bogs, and floodplains, have traditionally been treated as nuisances by city planners intent on expanding their borders or establishing new developments where none existed before. Famously, Tsar Alexander the Great of Russia decided to build a new capital on the Baltic Sea. About 20% of the proposed city land was marshland; a castle was to be constructed in the middle of a giant swamp, and an impassable slough occupied the center of town. While St Petersburg was eventually completed, it has suffered over 300 floods in its 300-year history.
Destruction of wetlands in the US and around the world removes some of the most effective natural flood-control measures available, and many devastating floods along the Mississippi and Missouri Rivers in recent decades have been exacerbated by practices which sever the connection between the rivers and their floodplains.
Floodplains are natural low-lying areas adjacent to rivers which remain dry most of the time, while wetlands are usually found within floodplains and are covered with water seasonally or year-round. When rivers overflow their banks, often due to excessive rainfall far upstream, the water enters the floodplains and wetlands, which can rapidly absorb excess water or filter and store it.
As urbanization has expanded, the demand for riverfront properties have exploded. Factories reliant on the river for water and waste discharge, ever-expanding commercial centers and the ports to serve them, and high-end residential developments marketing the charm of riverfront views. In each of these cases, riverside development is likely tied to destruction of floodplains and the elimination of natural protections.
In order to allow the environment’s natural safeguards to function, urban planners need to protect existing floodplains and wetlands and restore or establish new ones. The severity and frequency of disastrous flooding are increasing even as droughts wreak havoc on water supplies and agriculture. Changes in weather patterns is making events more intense and unpredictable and major floods are part of the result.
Fortunately, artificial wetlands can serve similar functions even in urban areas. They can be constructed in naturally low-lying areas and designed to accept and detain incoming stormwater where it can be naturally filtered and released slowly back into the ecosystem. See the next article for a more detailed discussion of constructed wetlands.
