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Natural Flood Protection In The US South

Guest post written by Ha Do, a Dogwood Alliance intern.

While all of the United States is focusing attention and resources to handle and recover the economy from the COVID-19 pandemic, the Atlantic hurricane season is returning to the US South. The season this year is forecasted to be more active than a normal year, so floods are also expected.

The US South is heavily affected by floods.

Among the ten states most likely to flood in the next 100 years, five are in the US South. Every year in the US South, flooding costs lives and billions of dollars. It devastates livelihoods and forces thousands of people to flee their homes. In June 2019, the Arkansas River flooded, which caused damages to homes, agriculture, roads, bridges, and levees focused across Eastern Oklahoma and Western Arkansas and cost more than $3 billion. Five lives were lost. Tropical Storm Imelda in September 2019, which came with 3 feet of rainfall over a three-day period, caused a severe flood in Southeast Texas, costing more than $5 billion in damages and five lost lives.

Flooding in New Orleans, Louisiana

The global pandemic will make dealing with hurricanes and flooding more difficult this year. Moreover, existing challenges from climate change lead to floods with higher intensity and frequency. Our traditional approach to flood prevention, which relies heavily on manmade “gray infrastructure”, also known as constructed infrastructure, such as dams, levees and spillways, is no longer sufficient to deal with the flood risks in the future. Nature-based measures, such as living shorelines, restored wetlands, reforestation projects, rain gardens, and green (vegetative) roofs, therefore, have become a more effective approach to flood risk management.

Why do we need nature-based solutions for flood risk management?

Traditionally, flood management relies mainly on gray infrastructure. However, according to a recent study, these works “have straightened, steepened, and narrowed the river, and [our] research has shown that these changes cause floodwaters to flow higher and faster.” In addition, most of these structures are designed to cope with floods in the “a mid-20th century climate.” They are no longer suitable under existing and changing conditions. However, expanding or upgrading gray infrastructure is an expensive and inefficient option.

In contrast, nature-based solutions are an effective complement or substitute to gray infrastructure because they help reduce flood risks through three main mechanisms. First, restoring ponds and wetlands and connecting floodplains increases flood water storage capacity, preventing or slowing down runoff during heavy rains. Second, other measures, including rain gardens, changing agricultural practices, and increasing soil permeability will help increase the amount of water absorbed into the soil or increase evaporation into the air, thereby reducing runoff water. Third, planting trees and hedgerows, salt marshes, coral and oyster reefs, and restoring meandering rivers are all actions that can slow water flows, thereby mitigating damages caused by fast-flowing floodwaters. These measures, when implemented together, can help prevent flooding in flood-prone areas of the US South.

Not only is it effective in reducing flood risks, nature-based solutions have other advantages.

Nature-based measures are more cost-effective compared to traditional gray infrastructure.

In one study, wetland restoration brought about more than $8 in benefits from flood reduction for every $1 of investment. Similarly, protection of oyster reefs can generate $7 for every $3 of investment. This is far more cost-effective compared to the ratio of gray infrastructure, such as levee construction (a $1 benefit for every $1 invested ratio). Moreover, conserving nature can be about 30 times more cost-effective than building seawalls. Another study indicates that across the US, the annual savings in terms of flood losses avoided would range from $63 to $136 million (2011 dollars, which if adjusted for inflation would be even greater) if more nature-based measures are implemented.

Nature-based solutions are more flexible.

When there is sufficient space, natural solutions, such as shorelines and natural floodplains, can adapt to different levels of river and seawater, while ensuring ecosystem values. Well-designed natural measures will increase adaptiveness and resilience for areas, especially under climate change conditions.

Natural-based solutions also bring along many co-benefits.

These benefits include, but are not limited to, biodiversity conservation, improved water quality, food production, recreation, and carbon storage. Therefore, nature-based measures are thought to be a win-win solution for both conservation and flood prevention.

Considering the technical and cost effectiveness as well as specific natural conditions, such as long coastlines, wetlands, and rich forests in the US South, adopting nature-based solutions is an appropriate and sustainable choice to cope with flood risks and should be strongly promoted in the region.

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Ha Do is an international student from Vietnam who has been actively working to protect water resources and the environment in her home country. Coming to the US to complete her master’s degree in Environmental Management at Duke University, Ha feels connected with the wilderness of the US South and wants to contribute to the communities that she’ll be a part of for the next two years. She has been engaged in various environmental education activities and the arising climate movements in North Carolina. Ha loves travelling and exploring other cultures through their cuisine.

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