Green Infrastructure Coalition, A project of the Environment Council of RI
Green Infrastructure Coalition

Stormwater and Climate Change

Image Credit: Woonasquatucket River Watershed Council

Woonasquatucket River floodwater backing up behind the Valley Street bridge in Providence on March, 31 2010.

As Rhode Island experiences more intense storms resulting from climate change, we must reduce the causes of climate change at the same time we mitigate the effects of heavy rains and storm surge to our 400 plus miles of ocean-facing and bay coastline. Locations in the floodplains and at the mouths of rivers naturally flood. Flooding damage is magnified as the impervious, hard surfaces of the urban and suburban landscapes prohibit water from soaking into the earth. Dry lawns, driveways, roofs, streets and highways pour stormwater into swollen rivers that are met, in hurricanes and nor’easters, by rising water of bay and ocean.

Mitigating the Flow at the Source

Many sources increase flow downstream, starting with the wash from roof drains flowing onto driveways. Urban parking lots paved curb to curb dump gallons of water into the street sewers. Green infrastructure — in the form of residential rain gardens, neighborhood green spaces, and parking lot buffers at the thousands of sources around Rhode Island — absorbs significant stormwater.

In 2012, Environment Council of RI identified urban climate adaptation as a focus area. With support from the National Wildlife Federation and the RI Foundation, ECRI brought together a working group to explore climate challenges in urban under-served communities. The project’s final report, “Exploring Climate Change Resilience Strategies in Rhode Island Urban Under-served Communities,” recommended, “Remove pavement and increase greenery where possible: Promote green space, permeable surfaces, and trees in all planning for future land use and roads in urban centers. De-pave vacant lots whenever possible.”

Gray and Green are Complementary

In Newport and Providence stormwater was designed to flow into septic sewer and overflow into nearby water. The problem in Providence was mitigated but not totally fixed by an $1.3 billion project to build gray infrastructure — pipes leading to massive tunnels to store stormwater until it could be treated and discharged into the Bay. Bay water quality has benefitted from diverting the overflows to treatment. The Narragansett Bay Commission CSO Abatement Project.

However, Green Infrastructure, where appropriate reduces the size for massive gray projects, and the green projects cost less with good environmental results. Cost-Benefit Resources | Green Infrastructure | US EPA. Trees mitigate urban temperatures with shade while storing water and cycling it. Shrubs and landscaped areas increase neighborhood cohesion while holding the soil against flood erosion.

Community Effectiveness

Municipal planners, environmental organizations, and citizens work together for coordinated reduction of stormwater. This process advocated and implemented by the Green Infrastructure Coalition has social, environmental, economic benefits as we plan for resilience following climate changed weather.

Students working in the summer of 2015 with Clean Water Action developed strategies for working at the neighborhood scale to identify opportunities for green infrastructure.

The National Wildlife Federation has developed a guide for helping community planning for climate resilience.

Cool Cities

The sun sinks into asphalt, concrete, and brick creating heat islands, and along with other factors makes cities much warmer than farm or forest. Heat illness and mortality increase when cities do not cool down at night and when air pollutants collect at night. As heat increases so does the use of air conditioning, demanding more electricity and producing more greenhouse gases that contribute to climate change.

Using trees in stormwater-mitigation landscapes provide shade to mitigate the heat island effect as they prevent the rays of the sun from absorption in the brick and cement. Instead, during the growing season when the heat island effect adversely affects life, the sun’s energy hits foliage where it is used for photosynthesis rather than heating brick and asphalt. Obviously in cities where buildings are taller than trees, the rise above 2 or 3 stories will continue to absorb energy.

Air pollution can be trapped at night in local inversions caused by overheated pavement and buildings. The production of surface-level ozone is also enhanced by high temperatures of heat island effect (EPA: Reducing Urban Heat Islands: Compendium of Strategies Trees and Vegetation).

Coastlines on the Edge — Where Storm Water Meets Storm Surge

An estimated 3-5 feet increase in sea level will occur by 2100. Increasingly here in Rhode Island we are witnessing the impacts of accelerated sea level rise as extreme high tides inundate our low lying neighborhoods and roads. Along the coast where large river systems empty into the sea, flooding magnifies when stormwater run-off from a large river watershed funnels an intense rain event to meet the high tide or storm surge from the sea. Coastal resilience efforts can help reduce the impacts of flooding and erosion, and also can enhance and restore natural systems as part of the defense.

Nature’s green infrastructure at the coast includes salt marsh, oyster reefs, dunes, barrier beaches, and maritime forests. These natural shoreline features attenuate—moderate-- waves and decrease erosion and flooding. Today we are seeing efforts to replicate natural systems through nature-based infrastructure, where a combination of natural and engineered features are designed to mimic nature with the goal of reducing coastal flooding risks and enhancing ecosystem services.

Knowledge of the combined effects of coastal hazards and local stormwater dynamics, both for today and for the future’s rising sea level and increased storm intensity, is key to understanding what areas are appropriate for green infrastructure or gray infrastructure, and which techniques would be most effective along the coastline. Given the confluence of land and sea at the coast, it is critical to implement objectives of reducing stormwater volume and contamination from uplands and agreeing where coastal inundation and impacts will occur.

Expertise from both upland and coastal disciplines must be at the policy, planning, and permitting tables. Developing resilience means acknowledging the power of water: retreating where the land will not stand up to the sea, designing buildings with inevitable sea level rise and storm surges understood, spending public money on the basis of knowledge of where the tides will rise and not where the funded projects will wash away, and protecting private interests from the folly of ignorance.