Seawater Intrusion

Table of Contents

Introduction

Causes of Seawater Intrusion

"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."

"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." - https://phys.org/news/2021-06-coastal-overtopping-world.html

Asia

Dangers of Seawater Intrusion

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.


Salt Front


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."

Countries Most Prone to Urban Flooding

Sea Level Rise 

"By 2100 in the USA, coastal population growth and sea level rise could put between 4 and 13 million people at risk of inundation"

Dangers of Seawater Intrusion

Damaged Ecosystems

Ghost Forests

These are caused by sea level rise bringing salt water into forest that are no adapted for the salinity. The forests die, releasing methane and other green house gasses as they turn to marshlands.


"Drowned trees in what scientists call "ghost forests" increased the amount of carbon dioxide released by these ecosystems by about 25%, according to a study."


"Before conducting the new study, Martinez said some researchers thought the dead trees were acting as straws to suck up greenhouses gases from the soil. When the tree dies, remaining water is flushed out of the leaves, which they thought would allow greenhouse gases to diffuse up the tree.


But their research showed that higher tree stems hold less greenhouse gases than they thought.


She added that they are still unsure how greenhouse gas emissions differ between tree species and how to advise land managers on mitigation efforts. Some researchers have suggested implementing "living shorelines" made from plants and rocks to buffer saltwater surges.


"It's a hard question to answer because snags can become a new habitat for other animals," Martinez said. "We're hoping to get a better idea of how greenhouse gases change as the trees are dying and also get better estimates of live tree stem emissions." 

" In the United States, ghost forests are most common along the Atlantic coast, from Canada to North Carolina, as well as in Louisiana.


Yet as ominous as these eerie ecosystems appear, Kirwan’s research has shown that they are not a sign of impending doom. Instead, ghost forests actually offer evidence that the natural world is responding to climate change, and resiliently transforming to survive sea level rise. By sacrificing a strand of trees along the coast, the newly-formed marshland can protect the forest and other land further inland.


Salt marshes are one of the most productive ecosystems on the planet, and they are effective buffers, protecting inland regions from storm surge. “This creation of ghost forests is a sign that marshes are being preserved,” Kirwan says. “They are migrating.”


It’s unclear when ghost forests were first scientifically described, but research started ramping up in the 1980s. And yet, scientists are only just now beginning to understand the complex effects they have on the environment. According to the Virginia Institute research, for instance, carbon sequestration rates may be higher in ghost forests than in the original forest, because the wet soil and healthy marsh ecology replaces the dry forest floor.


However, other research has shown that among the most likely plant species to colonize marshlands are the phragmites, a group of perennial grasses. Phragmites sequester less carbon than trees, meaning coastal deforestation could instead lead to more carbon dioxide in the atmosphere.


There are many questions begging for answers: how plants and animals are affected by ghost forests, the impacts of coastal deforestation and how long these types of marshlands will be able to protect inland areas from flooding."


"...New marshland should be able to buffer against some sea level rise, but may not be able to keep this up for long." 

"Ghost forests are expanding along the East Coast due to a combination of drought conditions and tropical storms. Trees in wetland areas are dying at increasing rates because they are exposed to saltwater more often; a flood or storm surge that may have occurred once in 100 years in the past may now occur once every 20 years or more. This consistent exposure to saltwater can damage the roots of trees, keeping them from absorbing the freshwater and nutrients they need to grow and thrive."


"... Runoff from agriculture and wastewater ditches can also create pathways for saltwater to intrude upon wetlands and forests, contributing to their decline. This information is key for changing how agricultural workers, environmental managers, regional climate mitigation planners and others interact with one another and the environment that supports us all."

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.

Water Salination

Seawater Intrusion

Impact on Agriculture

"Organized farming fed the first cities 4,000 years ago. The Tigris and Euphrates rivers made it possible to grow wheat on the arid Mesopotamian plains, but the dry climate eventually defeated human engineering. Irrigation brought water to fields faster than it could drain out. As salt-rich groundwater rose and surface water evaporated, mineral salts built up in the soils. Farmers switched to more salt-tolerant grains like barley, but the harder they farmed, the less they harvested. After about 2,000 years, the once-fertile land of southern Mesopotamia was barren." - Smithsonian Environmental Research Center: In Ancient Mesopotamia 

Unsafe Drinking Water

Water sources including wells and stepwells are already suffering from groundwater salination. In certain areas, underground water is totally unsafe to drink due to the toxic levels of ground water contamination.

Stepwells for example have been used for drinking and bathing for thousands of years, but in certain locations, abuse of water or chemicals in the ground water can make the water in certain stepwells unsafe for human use.

Solutions

Living Shorelines

For centuries humans have destroyed natural coastlines in order to create hard coastline. However modern understanding of how the elements interact with these shows that we can boost biodiversity and soften nature's blows on our infrastructure when we opt for softer, living shoreline infrastructure.

Mangroves

These specialized forests full of salt-tolerant plants helps protects coastlines from erosion and storm intrusion slowing the destruction of coastal farmland and coastal communities.

How Mangrove Forests Protect The Coast

12 second video of a tank demonstration showing how mangroves absorb and neutralize wave energy before it hits dry land.

Oyster Reefs

These can exist in or near the mouths of rivers, in bays and wetland, as well as the shallower areas along coastlines and island. They protect against coastal erosion, sea level rise and inundation. They sequester carbon, clean polluted water, reduce ocean acidification, and provide important habitat for many species.

Coral Reefs

These tend to lie farther out to sea, and help slow the impact of incoming waves and storms before they reach our shorelines.

Tree Planting

Establishing and protecting riparian borders can be a very powerful tool to protect water quality, mitigate flooding, control erosion, increase biodiversity, create wildlife corridors, protect ground water, and even improve water respiration to provide vital rain for crops.

Pollution Major storms and floods can damage buildings, overload sewers, farms, and chemical storage facilities. Waste is picked up from damaged buildings, road ways, and tipped bins sending a huge array of unknown chemicals, bacteria, and other microbes into people's drinking water, soil, and air.

Increased Illegal Sewage Releases

Sea Walls

Floating Buildings?

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."

 - https://phys.org/news/2021-06-retreat-war-climate.html 

Careful Choice in Relocation/Building Site Choices

There is some information about this topic on our Buy Out Programs page.

Coastal Defenses

Man-Made Defenses

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.

Mangroves

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.

Upgrade & Redesign Seawalls

Protect Waterways from Seawater 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." - 

Sustainable Drainage Systems (SUDS)

SUDs passively reduce flooding down stream by slowing the flow of water, letting it spread out in safe places so that it can better infiltrate the soil. This has many benefits from reducing erosion and siltation, to recharging ground water and making the landscape more resilient against droughts, fires and heatwaves. 

Recharging ground water also means salt water intrusion can be reduced along coastal areas, while guaranteeing safe ground water for future generations.

Click the SUDs button to learn more about these systems.

Beavers are a keystone species that naturally lives throughout the northern hemisphere in North America, Europe and northern Asia from Russia down to at least Mongolia. These natural engineers were perhaps the first major designers of SUDs, and can provide many of the same benefits without requiring paychecks. Click the Beaver button to learn more about how to help these animals return to the places that need them, or to find out which organizations near you might help remove and rehome some that are causing unwanted flooding.

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.

Examples of Green Spaces

Green spaces can perform a number of services, and incorporating green spaces in flood prevention plans can even boost their success and biodiversity.

Greenbelts and greenways are strips of green areas connecting communities while tamping down excessive urban sprawl. These spaces reduce air pollution, provide connectivity for wildlife, and if properly designed can provide connectivity to humans instead of forcing everyone to drive in private vehicles. Greenbelts can absorb flood water, but this may result in people having to take alternative routes such as roads until the waters recede.

Wetlands are vital for many migratory and stationary species. Seasonal rains can turn deserts, grasslands, and other biomes into vibrant space for pollinators as well as other species who feed on them. Flooding may negatively impact tourism, but should be less likely to destroy homes unless indigenous communities or park rangers live in the area.

Wetlands

Wetlands are natures sponges, and have been under threat from farmers and urban developers draining these natural resources. By restoring wetlands we both buffer land and communities from storms and floods, but we'll also restore biodiversity for millions of species who rely on wetlands to reproduce, eat, and find refuge year round or on their migration routes.

Tools

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.

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 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.

Finance & Facilitate Systems to Recycle Water

"Recycling greywater frees up more finished water for other uses, expanding supply and decreasing the need to discharge into receiving waters. Receiving water quality limitations may increase due to more frequent droughts. Therefore, to limit wastewater discharges, use of reclaimed water in homes and businesses should be encouraged." - https://www.epa.gov/arc-x/climate-impacts-water-utilities#tab-3

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." - https://www.epa.gov/arc-x/climate-impacts-water-utilities#tab-3

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.

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.

Model and Reduce Agricultural & Irrigation Water Demand

"Agriculture represents the second largest user of water in the United States in terms of withdrawals. In order to forecast and plan for future water supply needs, agricultural (irrigation) demand must be projected, particularly in drought-prone areas. For example, to reduce agricultural water demand, utilities can work with farmers to adopt advanced micro-irrigation technology (e.g., drip irrigation)." - https://www.epa.gov/arc-x/climate-impacts-water-utilities#tab-3

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.

Resources

Groups

Africa

Madagascar

Asia

Cambodia

Europe

United Kingdom

The Wildfowl and Wetlands Trust "We conserve, restore and create wetlands, and inspire everyone to value the amazing things healthy wetlands can do for us."

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.

To learn about our policies, read our A 10-Point Platform on Climate Change."

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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.

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Grants & Funding

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North America

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