Coastal Overtopping

Table of Contents

Introduction

"Low-lying coastal regions host nearly 10% of the world's population. In addition to ongoing erosion and rising sea levels, these areas and their unique ecosystems are facing destructive hazards, including episodic flooding due to overtopping of natural/artificial protection, as in the case of Hurricane Katrina, which hit the United States in 2005, Cyclone Xynthia in Europe in 2010, and Typhoon Haiyan in Asia in 2013 (the largest tropical cyclone ever measured). These episodic events are expected to become more severe and more frequent due to global warming, while the consequences will also increase due to increased anthropogenic pressure, such as coastal and infrastructure development, rapid urbanization. Although the magnitude and frequency of these events remain uncertain, scientists believe that countries in the tropics will be particularly affected."  - An Acceleration of Coastal Overtopping Around the World

"The combination of tides and episodes of large waves is the main contributor to episodes of coastal overflow," says Rafaël Almar, a researcher in coastal dynamics at IRD, and the coordinator of the study. "We identified hot-spots, where the increase in risks of overtopping is higher, such as in the Gulf of Mexico, the Southern Mediterranean, West Africa, Madagascar and the Baltic Sea."

"The scientists also performed an initial global assessment of the potential coastal overtopping over the 21st century, by taking into account different sea-level rise scenarios. Results show that the number of overtopping hours could increase with a faster pace than the average rate of sea-level rise. "The frequency of overtopping is accelerating exponentially and will be clearly perceptible as early as 2050, regardless of the climate scenario. By the end of the century, the intensity of the acceleration will depend on the future trajectories of greenhouse gas emissions and therefore the rise in sea-level. In the case of a high emissions scenario, the number of overtopping hours globally could increase fifty-fold compared with current levels," Rafaël Almar warns. "As we go along the 21st century, more and more regions will be exposed to overtopping and consequent coastal flooding, especially in the tropics, north-western United States, Scandinavia, and the Far East of Russia."

Further studies will be needed on the local and regional levels to flesh out these global projections, which provide a solid basis for proposing effective adaptation measures in the hotspots identified." - An Acceleration of Coastal Overtopping Around the World

Dangers of Coastal Overtopping

Flooding

Perhaps the most obvious impact of coastal overtopping is the flooding which brings property damage, and poses various dangers to communities.

Sunny Day Flooding

This happens when there is no rain or storms, but can be caused by king tides. Thanks to climate change, these once-rare occurrences, are becoming yearly, monthly, or even weekly for coastal communities around the world.

Sea Water Intrusion

This happens with waterways, as tides bring seawater further past the mouth of these waterways, killing freshwater species, and causing other problems. Thanks to sea level rise, this problem is getting worse, and to the point that some coastal communities which traditionally relied on their local waterways for freshwater, are now finding their drinking water contaminated by sea salt.

Seawater intrusion is also an issue when seawater makes its way into aquifers. This can happen via waterways, or via coastal overtopping.

Solutions

Managed Retreat

"... the purposeful movement of people, buildings and other assets from areas vulnerable to hazards—has often been considered a last resort. But Siders said it can be a powerful tool for expanding the range of possible solutions to cope with rising sea levels, flooding and other climate change effects when used proactively or in combination with other measures."  - Managed Retreat: A Must in the War Against Climate Change 

Buy Out Programs

Buyout programs can help residents with limited financial assets safely move to safer locations, while the acquired land can be used for coastal defenses and carbon sequestration.

Indicators

When considering our options, including managed retreat we need to be aware of the resources and warning signs that may indicate it is time to leave an area or start mitigation practices.

Ghost Forests

Communities will need to decide which areas they allow to become ghost forests and which will need to be protected by seawalls or other options. Communities may choose to allow ghost forests to turn into salt marshes, while picking new places for replacement trees to be planted. Strategic tree planting, especially along water ways can help recreate riparian buffers that will minimize erosion, sedimentation, pollution, and flooding higher in the watershed, which could allow for better protection along new coastlines.

Salination of soil and Aquifers

"Sea-level rise, in combination with increased groundwater pumping can increase saltwater intrusion in groundwater aquifers. Saltwater intrusion into groundwater aquifers can increase treatment costs for drinking water facilities or render groundwater wells unusable.


As the sea levels rise, the “salt front” (location of the freshwater-saltwater line) may progress further upstream. This encroachment may be further exacerbated by drought, reduced rainfall or changes in water use and demand. Saltwater intrusion can result in the need for water utilities to increase treatment, relocate water intakes, or development of alternate sources of fresh water.


Saltwater intrusion, through surface or ground water sources, may diminish the availability or quality of source waters for drinking water utilities."

Factors to Consider for Managed Retreat

Create and Enforce Legislation Banning New Developments in Flood Zones

In areas without this type of legislation, many people have been sold home in known flood zones, within 100 year flood zones, and other unsuitable places. These homes are prone to repeated flooding which can push families into a poverty situation where they are unable to sell their homes (because they flood repeatedly) which leaves them without the funds to leave or keep rebuilding. Governments need to offer buy-out programs and work with conservation organizations to clear the badly-placed buildings. The land can function as both wild space and as permeable land to help absorb future flood waters, protecting nearby communities.

Relocation Site Choices

If your plan is to move people and communities, you need to ensure the next place isn't going to be in imminent danger of sea level rise as it runs its course, or any other natural disasters. 

5 Best (and Worst) Places to Build a Home or Village

This 10:33 minute video talks about how different locations can be more dangerous in respect to floods and fires, or advantageous in respect to view, resources, and utility efficiency.

There is more about this topic on the Flooding page.

Coastal Defenses

Preserve Wetlands, Waterways, and Mangroves

Mangroves not only help prevent soil erosion, but help protect communities against hurricanes and other extreme weather. They have unique biodiversity, and serve many functions but are under threat from climate change, and human activities. Wetlands provide vital flood prevention with large spaces for overflow and absorption to take place. The vegetation both helps water sink into the soil and respirate back into the atmosphere. These wild areas also play a massive roll in preserving biodiversity for migrant and native species of fish, birds, and other wildlife. These in turn provide economic opportunities to the communities that preserve those ecosystems, while absorbing pollution so that it can do less harm.

Mangroves

Some places have been washed away so quickly after mangrove removal, that artificial barriers need to be build. Soon after soil has begun to rebuild, which may make mangrove replanting measures more likely to succeed.

Click the Mangrove button to learn more about mangroves or the Trees button to learn about free and affordable tree programs.

Salt Water Intrusion

Install low-head dam for saltwater wedge and freshwater pool separation "Rising sea levels, combined with reductions in freshwater runoff due to drought, will cause the salt water-freshwater boundary to move further upstream in tidal estuaries. Upstream shifts of this boundary can reduce the water quality of surface water resources. Installation of low-head dams across tidal estuaries can prevent this upstream movement." - 

Green Space Expansion

Green space is our greatest natural defense against flooding. These green spaces can be renovated to de-compact the soil and build flood mitigation infrastructure including reservoirs and swales. Ecologically these areas increase biodiversity, and can help expand our range of wildlife corridors which will further protect wildlife against the threats of extinction caused by fractured habitats. Keystone species, particularly beavers should be allowed to colonize these areas, providing flood protection in areas where human/animal interactions can be minimized.

Buy Out Programs

Buyouts help protect our most vulnerable citizens who, especially after many floods and damaging storms may not have the funds to keep rebuilding, nor to move away from dangerous, flood-prone areas. From a fiscal standpoint buyout programs reduce flood risk which reduces government liability and increased poverty which in turn increases strain on public funding.

Pollution

Pollution Sites Must be Maintained and kept far from Places that are expected to experience Flooding based on history or the proposed flood/sea level rise forecasts.

Sewage Facilities Need to be Revamped to Withstand or Work with Nature

Illegal sewage releases are becoming more common thanks to more frequent flooding and larger populations than some of these sewage facilities were designed to serve. Sewage releases during floods threatens water safety, and can spread deadly diseases to rescue workers, flood victims, wildlife, and domestic animals.

Water Management

Finance & Facilitate Systems to Recycle Water

If communities can't move and are already suffering the effects of seawater intrusion on their drinking water supply, then water recycling may help fill the humanitarian gap of access to safe water posed by salination of surface and ground water supplies.

Click the Grey Water button to learn more about recycling gently used water for uses including flushing toilets and watering gardens.

Click the Harvesting Water button and scroll or click in the Table of Contents to navigate down to the Water Recycling section where we have info about Tap to Toilet Water Recycling and Grey Water.

Practice Conjunctive Water Use

"Conjunctive use involves the coordinated, optimal use of both surface water and groundwater, both intra- and inter-annually. Aquifer storage and recovery is a form of conjunctive use. For example, a utility may store some fraction of surface water flows in aquifers during wet years and withdraw this water during dry years when the river flow is low. Depending on whether natural or artificial aquifer recharge is employed, the required infrastructure may include percolation basins and injection wells." - EPA: Climate  Impacts of Water Utilities

Return Land Drained for Grazing to it's Natural State

Reducing the consumption of animal products such as beef, wool, dairy, etc. will help reduce or even reverse our encroachment into wild places that traditionally acted as sponged for rain water. Some of these areas were actively pumped dry to allow grazing at the expense of valuable wetlands and forests, then over time compaction from animal hooves had mad many of these places suffer from increased erosion and soil compaction which stops water from penetrating. This means that fields can become prime causes of pollution and erosion, adding to flooding problems instead of working naturally as undisturbed wild places to do mitigate flooding.

Grazing uses the most land, is less efficient, meaning that "grass-fed" livestock take longer to reach slaughter-size while using more resources, and generally does not provide all of the benefits often touted by the livestock industry. For example carbon sequestration through well managed grazing, even in the best circumstances cannot reach a point of neutrality. The manure ends up directly on the ground where it can wash into water ways without any type of processing to reduce disease risk. Grazing is also the greatest cause of deforestation, which is problematic since trees are vital to water sequestration, fighting erosion, and reducing flood risk.

Ending subsidies to these operations would help prevent further destruction and expansion from this sector, while programs designed to support ranchers as they convert to plant-based agriculture will ensure that these people are supported in their time of need, while food and water security is ensured for everyone.

Click the Alternatives to Livestock button if you are a farmer who wants to find a more planet-friendly alternatives to raising animals or animal feed.

Plant Based Shift

Altering Our Farming Priorities via Diet Shifts, Wiser Distribution of Farming Subsidies to Help Farmers Transition to Sustainable Alternatives Away from Those Causing the Most Water Stress and Pollution How we raise our food is deeply tied to water shortages, flooding, water pollution, and poor land management including deforestation and draining wetlands to create artificial grazing land can add significant, costly complications to these issues. With most of our land used to raise livestock which give a relatively tiny percentage of protein and calories in return, critically rethinking our dietary systems and land use practices could relieve significant amount of room to rehome people, grow enough food for our growing population, AND perhaps even return damaged land to the wild for better flood mitigation. Below are some key issues that can provide the most impactful returns at the least cost to consumers or policy makers.

Click the Plant Based button to learn more about switching to plant-based alternatives.

Vertical Farms

These are perhaps best known for reducing water use in food production, however they can also provide resiliency against major events such as flooding. Crops left soaking in wet soil can become weak, or simply die and rot which threatens us with food insecurity while farmers and farm workers lose valuable income. Vertical farms are best suited for the types of crops eaten by humans: leafy greens, herbs, as well as fruits including berries, tomatoes, and cucumbers. They are not suited for crops commonly fed to livestock such as corn or other grains.

Eliminate Feed Lots, Factory Farms, and Manure Lagoons in Flood Prone Areas

Along water ways or in flood prone areas, these facilities endanger water safety. During major storms, farmers were unable to drain manure lagoons ahead of major storms which caused fecal mater and other contagious materials to flood into people's homes. Factory farm buildings filled with thousands of chickens and pigs were left to flood with the animals un-evacuated, meaning that after the flood waters receded, they were filled with rotting animal corpses, presenting further threat of dangerous diseases to nearby communities. - https://www.npr.org/sections/thesalt/2016/11/04/500701098/manure-happens-especially-when-hog-farms-flood

At the absolute least, any farmers already in these areas or applying for building approval should be required to submit their plan for full animal evacuation in the event of these storms as well as infrastructure to eliminate the risk of flooding manure into waterways or nearby communities. Similarly zoos, dog boarders, and other such facilities should be discouraged in flood-prone areas or areas that may contaminate waterways.

Tools & Apps

Water Pumping

The pumping of water takes a larger amount than many people realize. Pumping ground water for agricultural, industry, or public use, moving it between facilities, etc. all require energy since water is a fairly heavy substance.

Maps & Tools

Maps by Region Check specific State and Country pages to see if there are more specific maps, tools, projects, and groups for specific areas. If you have suggestions, we would love to hear what else we can include. Some states and countries have more detailed watershed, county, and city level maps. Other topic sections such as plastic, agriculture may be worth checking to understand how pollution enters our water ways, and how industries might endanger water sources without proper regulation, mitigation, or clean up systems to protect communities from these threats.

North America

USA

Organizations

Asia

Cambodia

Africa

Madagascar

Europe

United Kingdom

North America

USA

The goal of A2 is to help communities fight back. We do that by providing them organizing support, scientific and technical guidance, and better access to foundation and government funding. Most of all, our work consists of listening to our frontline leaders. Their experience, research, and solidarity guide everything we do, and offer a path toward environmental and social justice.

Supported by outstanding partner organizations with expertise in engineering, hydrology, public health, planning, and the law, A2 leaders have successfully halted developments in climate-vulnerable areas; implemented nature-based hazard mitigation strategies; organized home buyouts; and pushed for clean-ups at superfund sites, toxic landfills, and petrochemical plants.

We support everyone we can, but our special priority is people who have suffered the worst environmental impacts for the longest time; that usually means low-income, Black, Latinx, Native American and other underserved communities.

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