Hard Engineering
Table of Contents
Introduction
In the context of coastal defenses, "Hard engineering includes groins, jetties, seawalls, revetments, and breakwaters."
Benefits of Hard Engineering
Erosion Prevention & Land Reclamation
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.
Biodiversity Boosting
"Cracks and crevices between the jetty stones are home to seaweeds, crabs, sea anemones and the like. Most were swept in as larvae by the Gulf currents or came from oyster reefs in a bay. Some were transported from distant seas on ocean-going vessels.
Organisms on Texas jetties live in zones just as they do on natural rocky shores. Some stay above the high tide mark with the periwinkles, some thrive with the barnacles between the tide lines and some remain with the seaweeds below the lowest tides." - Texas Parks & Wildlife Department: Flora Fauna Guide: Jetties
Problems with Hard Engineering
Hard Engineering Can Cause Damage
Hard engineering can often cause increased erosion, or even prevent natural beach regeneration, so it is vital to ensure it is only used where appropriate, with living shoreline options considered first during planning.
"Due to the adverse effects of shore parallel structures, alternatives are strongly encouraged and actively sought by the National Park Service. However, in cases where valuable resources are not feasible to relocate such as cultural landscapes and associated sensitive cultural and historic assets, seawalls, revetments, and bulkheads significantly reduce asset vulnerability. This is the case for seawall repair projects at Ellis Island, a part of the Statue of Liberty National Monument. Other parks such as Golden Gate National Recreation Area, California, are examples of how to manage active coastlines in a highly developed area. Still, hard structures are removed whenever possible to support the National Park Service mission of restoring natural coastal processes. This will likely be the case for Sand Point, Pictured Rocks National Lakeshore which has experienced amplified erosion since instillation of a rock revetment in the mid 1980’s. Planned removal of the structure will restore the beach’s ability to naturally accrete sediment." - National Parks Service: Seawalls, Bulkheads and Revetments
Legal Issues
Bans
"Historically, North Carolina has tried to avoid the problems that can be brought on by the use of hard structures to control erosion. In 1985, the North Carolina Coastal Resources Commission (CRC), a policy-making body for the coastal management program, studied the effects of hard structures on beaches in other states. The CRC concluded that the potential negative effects of such structures could cause irreversible damage to North Carolina’s beaches. As a result, the CRC recommended banning the construction of hard structures to protect buildings at the coast. The ban made exceptions for protecting historic buildings that could not be moved and for maintaining important waterways needed for navigation, such as Oregon Inlet in Dare County.
The regulatory ban on hard structure existed in practice for 15 years before it was upheld in court in a 2000 case. In 2003, the North Carolina General Assembly voted unanimously to formally adopt the hard structures ban as law. The law banned the construction of most new, permanent erosion control structures on the beach but contained the same exceptions as the regulatory ban.
The state’s environmental community has consistently supported this prohibition on these hard structures." - North Carolina Coast: Terminal Groins
Permitting
Permitting can take a lot of time and money, while living shoreline projects might not require the same amount of resources to start or complete.
Types of Hard Engineering
Breakwaters
"A breakwater is an offshore shore-parallel structure that “breaks” waves, reducing the wave energy reaching the beach and fostering sediment accretion between the beach and the breakwater. Made of rock, concrete, or oyster shell, these structures can be floating or fixed on the ocean floor and can be continuous or segmented. Breakwaters can be placed attached to the shoreline as headlands or submerged near the shoreline as sills. Breakwaters allow for the accretion of sediment between the structure and the shoreline, potentially stabilizing wetlands and providing shelter for new intertidal marsh habitat. However, this may impede longshore transportation of material leading to downdrift erosion as well as form intertidal marsh not appropriate for the location, replacing natural sandy beach habitat. Coastal parks hosting historic resources, such as Colonial National Historic Park, can be seen utilizing these techniques to dissipate wave energy and protect inland sites." - National Parks Service: Breakwaters, Headlands, Sills and Reefs
Groins or Groynes
"A groin is built perpendicular to the coast and works similar to the way a jetty works. But groins are usually smaller than jetties and built on straight stretches of beach, not near inlets or channels." - North Carolina Coast: Terminal Groins
Jetties
Submerged Near-Shore Breakwater
Living Breakwaters
Living breakwaters take ecosystems into consideration, and supply wildlife with safe places to hide, nest, and forage. These can be considered a type of living shoreline!
Seawalls
"Shore parallel structures include seawalls, bulkheads, and revetments. These structures are designed to protect resources behind them from the impacts of wave energy and associated erosion. Although they hold soils in place behind the structure, seawalls usually accelerate erosion on adjacent beaches. The structures impede natural landward migration of beaches in response to sea level rise, halting upland growth of new beach. In some instances, the beach migrates entirely to the base of the seawall and disappears completely (passive erosion). Wave energy is reflected off seawalls, increasing erosion at the toe of the wall (active erosion) and subsequently from adjacent beaches as well. In many areas, beaches have completely eroded and disappeared on account of seawalls." - National Parks Service: Seawalls, Bulkheads and Revetments
Vertical Seawall
Recurved Seawall
Revetments
"Revetments, like seawalls, protect resources landward of the structure but likely at the expense of the seaward slope. Materials such as armorstones, stepped concrete, or rip-rap stones are placed directly in the existing slope face to absorb wave energy and strong currents." - National Parks Service: Seawalls, Bulkheads and Revetments
"Bulkheads provide a similar purpose but are vertical standing structures running parallel to the shoreline, often constructed of rock-filled timber cribs and gabion, steel, or concrete." - National Parks Service: Seawalls, Bulkheads and Revetments
Stepped Revetments
Sloped Revetments
Rock Armor
Tools & Guides
Wave Tank Demonstration Showing the Impact of Coastal Defences on Flood Risk 12:22 minute video from the JBA Trust
12:22 minute video showing how waves can cause overtopping, and how different types of coastal defenses can protect coastal areas, and which have . Examples include a vertical seawall, recurved sea wall, stepped and sloped revetments, rock armor, and submerged near-shore breakwater.
Alternatives to Hard Engineering
Living Shorelines
This option is listed as an alternative, but living shoreline strategies can be mixed in with hard engineering solutions. Living shorelines are often preferable, but in certain situations a combination of hard and soft engineering can help strengthen coastal areas while contributing to local biodiversity.
Reefs
Before waves even make their way to shore, various types of reef can help reduce wave energy.
Trees
Groupings of trees can help reduce flooding and minimize wave energy. Their roots physically help hold soil or aquatic sediment in place.
Wetlands
These come in many types and act like natural sponges against flooding from both rain and ocean action.
Sponge City Solutions
Away from shorelines, we still have some power over the way water moves through our communities, and flows out to larger bodies of water.
These solutions can be large and small, working together to create a patchwork of efficiency and boosted biodiversity.
Planned Retreat
In situations where erosion, flooding, and/or sea level rise are too costly to combat, strategic retreat may be the best option.
Codes & Ordinances
North America
USA
North Carolina State Building Code-2009 "In 2023, the Federation successfully lobbied the state General Assembly to cover residential docks that are built along our coast back under the state’s building code. This move will help ensure that any docks or piers are built in a way that will make them more resilient to damage during extreme storms."
Resources
Case Studies
Creating a Living Shoreline for Community Resilience (PDF) "AGU’s Thriving Earth Exchange helps American Venice preserve and persevere amid changing conditions"
North America
USA
Coastal Restoration Toolkit: Take Action to Restore Our Coastlines "Find tools and information you need to launch a restoration project in your community."
Green Infrastructure Effectiveness Database "This database is a compilation of literature resources documenting the effectiveness and economics of nature-based solutions and Green Infrastructure for coastal resilience."