Green Defense
Enhancing Coastal Resilience Using Green Infrastructure
As wet weather becomes an increasing problem in the coastal communities of Georgia, we look to green infrastructure as a resilient approach to managing the impacts. Green infrastructure is resilience based in nature.
How we build and where we build is important
Coastal Georgia's Green Infrastructure & Stormwater Management
Green infrastructure encompasses policies and practices that reduce stormwater and flooding impacts from the built environment and land development. It also focuses on protecting natural areas and working lands from development in the first place. This strategy works to preserve existing natural conditions, restore ecological functions to an area, or build with elements that utilize natural features.
Why do we need green infrastructure?
Residents of coastal Georgia are well acquainted with the frustration and devastation that storms and flooding bring.
As storms and hurricanes become more prevalent in the region, so do the economic impacts.
Dune erosion impacts coastal homes.
Wind causes mass destruction, leaving residents to deal with the economic responsibility.
Preparation for incoming storms has become an annual effort.
In our coastal communities, issues include not only flooding on the coast but also rivers. The study presented here focuses on "community resilience," why this concept should be built into human populations through green infrastructure, concentrating on protecting human life and property from external hazards. Scroll on to see the effects of wind and flooding with and without green infrastructure.
The Study
To understand the benefits that green infrastructure would have, researchers utilized computer software to model future storms with and without green infrastructure. A Geographic Information System (GIS) was used to gather, manage, and visualize spatial data. A FEMA tool called Hazus was used to estimate risk based on various storm levels. These tools were used to answer a simple question:
How much damage could be avoided with the use of green infrastructure?
Two pilot areas were studied to demonstrate the efficacy of green infrastructure practices in Southeast Georgia: Liberty County/Hinesville and Tybee Island. To capture a range of possible current and future conditions, a total of 118 wind and flood scenarios were modeled in these two Georgia communities.
Study Location: Tybee Island Coast
The City of Tybee Island, with a population of 3,000, is located adjacent to the City of Savannah and encompasses the entire island.
Tybee is a quaint barrier island that serves as a popular vacation destination, offering sandy beaches and historical attractions.
At this study location both coastal flooding and wind impacts were considered.
Impacts with and without an 8 foot sand dune were simulated to show potential destruction from flooding.
Hurricane wind impact on buildings was simulated with and without shutters to show the benefit of requiring shutters on new buildings.
Future scenarios included impacts from changes to storm intensity, sea level rise, and future development.
In a future category 1 hurricane, it is predicted that 1,685 buildings will be impacted by storm surge, at a cost of $76,394,392.
By implementing green infrastructure, which modeled a continuous 8 foot dune, the flooding was reduced as can be seen in the following images.
Future Coastal Flood Risk
In the above scenario, 426 buildings were saved with the implementation of green infrastructure on Tybee Island.
This is a savings of $41,955,782
Study Location: Hinesville/Liberty County
The Upper Newport River watershed encompasses a portion of the City of Hinesville. Within the watershed, a subset of streams were studied; Mills Creek, Peacock Canal, and Alligator Creek.
The historic City of Hinesville is the seat of Liberty County. It is one of the fastest growing cities in Southeast Georgia, and has a population of 33,000.
Extreme rainfall events cause rivers to flood.
At this study location, future rainfall models were created to show riverine flooding impacts with and without green infrastructure.
A reduction in impervious surface was mimicked as well as a reduction of input to riverine flooding.
In a future 1% annual chance rainfall event, it is predicted that 551 buildings will be impacted by flooding, at a cost of $20,709,060
When including the construction of future buildout in this scenario, the impacted buildings increase to 768 and a cost of $33,112,177
Future Riverine Flooding
In the above scenario, 87 buildings were saved with the implementation of green infrastructure by reducing impervious surface area.
This is a savings of $4,276,654
Predictions for the Future
With the intensity of storms and the resulting devastation that we have already witnessed, it's hard to imagine the situation becoming worse. However, research predicts the following to be seen in coming years
More intense hurricanes
Longer hurricane seasons
Poleward migration of hurricanes
Increased frequency
More rapidly intensifying storms
Slower moving storms
Less coastline protection
Floodplain expansion
As we move forward with these realities in mind, how can home and property owners protect their assets?
Including green infrastructure in communities has many benefits:
Increased property values
Increased water supply
Lower ambient temperatures
More walkable communities
Reduced water treatment costs
Cost savings
Improved air quality
Increased community resilience
Increased biodiversity
Habitat improvement and connectivity
Healthier communities
Improved water quality
Reduced flooding
Rain Barrels are inexpensive and easy to implement for small scale drainage areas. These containers intercept, divert, and store rainfall for later use.
By repurposing this water, stormwater runoff is reduced and demand on public water supply is also lessened.
Rain water harvesting tanks are a larger-scale version of rain barrels.
Reduction of demand on public water supply helps to protect groundwater aquifers from drawdown and seawater intrusion.
Dunes along the coast of Tybee Island are fenced off in an effort to protect them. These mounds of sand help absorb the impact of storms.
Restoration of plants in dunes helps to stabilize the sand; preventing erosion.
Dune crossovers allow vehicles emergency access to the beach while keeping the 8 foot dune intact.
A bioretention basin directs stormwater into a depression.
These landscaped excavations capture and temporarily store runoff until it can evaporate or infiltrate into the surrounding soil.
This reduces stormwater runoff and is less expensive than traditional drainage systems.
Permeable pavement is an alternative to traditional impervious paving surfaces.
It provides measurable reductions in stormwater runoff rates, volumes and pollutant loads by allowing water to pass through the surface into an underlying gravel base layer where it is temporarily stored and allowed to infiltrate into surrounding soil.
This reduces the need for larger and more costly stormwater management practices.
Storm shutters reduce the risk of broken windows during storms.
They can also save money on home insurance.
Current construction patterns in Hinesville and nationwide build right up to the edge of the floodplain boundary.
This does not take into consideration that floodplain boundaries will expand.
Because of this, floodplain management is important in addition to green infrastructure.
Wetland Conservation is an important component of protecting our landscape.
The coast of Georgia comprises a vast array of wetlands , boasting 368,000 acres of estuarine tidal marsh.
These marshlands provide a great buffer against flooding and erosion.
The Georgia Coastal Marshlands Protection Act states,
"This system is costly, if not impossible to reconstruct or rehabilitate once adversely affected."
Because of this, it is important to conserve our preexisting green infrastructure.
Low Impact Development (LID) is a planning and design approach to manage stormwater runoff, emphasizing on-site natural features that protect water quality.
Click the points in the map for local examples of low impact development
How does this apply to me?
Planning Tools
This tool and application were developed by partners at Georgia Tech and the Coastal Regional Commission. It generates a printable environmental quality summary report for user-defined areas in Coastal Georgia.
The map includes environmental features, accentuating green infrastructure, and Developments of Regional Impact submitted to the Georgia Department of Community Affairs.
