Dynamic revetments, also known as "cobble berms" or "dynamic cobble berm revetments", use gravel or cobble-sized rocks to mimic a natural cobble storm beach for the purpose of reducing wave energy and stopping or slowing coastal erosion. [1] Unlike seawalls, dynamic revetment is designed to allow wave action to rearrange the stones into an equilibrium profile, disrupting wave action and dissipating wave energy as the cobbles move. This can reduce the wave reflection which often contributes to beach scouring. [2] [3]
The goal is to create structures that are natural in appearance and function while providing acceptable protection to coastlines, combining the benefits of ecologically responsive shore protection methods with those of conventional armor‑stone revetments or seawalls. [4]
A line of logs can also be employed as upper reinforcement for a cobble berm. Drift logs are common on most shores in the Pacific Northwest. Their crisscrossed arrangement provides dynamic stability even when impacted by high tides and waves, capturing wind-blown sand and encouraging the growth of foredunes. [5]
Self-protection via landslides was demonstrated in the early 1990s when, in an effort to stabilize the Lone Tree landslide 15 km north of San Francisco, California Department of Transportation dumped excavated material including rocks and sediment sized from clay to large boulders down a steep cliff face, creating an artificial landslide. This experiment permitted the documentation of the early stages of landslide erosion, including the processes of waves cutting away the toe of the slide. It was observed that a beach immediately began to form along the toe of the eroding slide, consisting of the coarsest materials, gravel, cobbles and boulders. With its accumulation, the rate of toe erosion progressively slowed, the material having sorted itself into a protective gravel and cobble beach, backed in riprap-like fashion by a line of armor-sized boulders.
In 2017 DynaRev, a research project funded by the European Union, conducted a large scale laboratory experiment at the Large Wave Flume (Großer Wellenkanal) in Hanover, Germany. Its aim was to determine the performance and resilience of dynamic revetments to rising sea-level. [6] The response of a sand beach was measured for various water levels and wave heights, both with and without an upper cobble berm. During the experiment, the dynamic revetment demonstrated dynamic stability, as the individual cobbles within the structure moved with every wave but the global shape of the revetment remained stable. The researchers determined that dynamic revetments appeared to be a sustainable and affordable option for many locations experiencing coastal erosion where complete protection from coastal hazards is not needed and some coastal retreat is acceptable. [7]
In 2011, the Surfers' Point working group relocated the bike path and parking lot. To stabilize the area the project constructed a "cobble mattress" on the back beach. Sand was placed in the retreat zone to complement the cobbles and help rebuild the dunes. Later, the project constructed dunes using sand sourced from other beaches with excess sand. The project used grant funds from the California Coastal Conservancy and the Federal Highway Administration. [8]
Following storm damage to Cape Lookout State Park in 1999, some form of shore protection was sought. A conventional riprap revetment or seawall was deemed incompatible with this natural park setting, so the decision was made to construct a cobble berm that resembled the appearance and function of a natural cobble beach, backed by an artificial foredune that was reinforced by a core of sand-filled geotextile bags. Oregon Parks and Recreation Department completed construction of the 300-m long project by December 2000. [5]
In 1996 a rock jetty was constructed to protect State Route 105 near North Cove, which appeared to increase the erosion to the east by redirecting the force of the waves. In response, Washington State Department of Transportation constructed 780 feet of dynamic revetment along the south side of the highway right of way in the fall of 2017. The revetment generally performed as intended, with storm erosion transporting the berm material to the toe where it can buffer and dissipate wave energy. However, due to project footprint constraints, the cobble berm was constructed with a narrow width at the western end where wave energy is highest. This segment receives the brunt of waves that refract off adjacent riprap along the highway. Cobble re-nourishment was required several times during the first winter. [9]
In 2016, as a response to what has been called the fastest erosion on the West Coast of the United States, the community of North Cove began placing unsorted pit-run basalt of predominantly cobble size along nearly 2 miles of shoreline to slow the erosion while engineers worked on a more permanent design. [10] The community nonprofit group Wash Away No More supported the project through fundraising and work parties. [11] Working with regulatory agencies, the principles of Adaptive management and Design with Nature were incorporated into the project to allow for learning and change based on periodic monitoring by Washington State Department of Ecology. As part of the monitoring, PIT tags were placed in individual rocks and their motion tracked over time. It was observed that the rocks that moved farthest weighed between 1 and 10 kg (2.2 and 22 lb) with an intermediate axis of about 10 to 20 cm (4 to 8 in). Angular and rounded rocks appeared to perform equivalently in this environment. Technical assistance and funding were provided by the Pacific County Conservation District. The lost beach quickly returned. [12] [13] [14]
As Chairman of Pacific County Drainage District #1 and with support from Wash Away No More and the Pacific Conservation District, local cranberry farmer David Cottrell led the project through all phases from conception, construction, and adaptive management between 2016 and 2023. David undertook significant hands-on work alongside the local community to ensure cobble levels were maintained and carried out pioneering experiments on how and where to place cobble volume and the use of local driftwood to enhance coastal protection. This work drew the attention of coastal engineering academics in the USA and internationally, and David co-authored several papers on the topic of dynamic revetments [7] [15] [16] [17] .
A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc shells or coralline algae. Sediments settle in different densities and structures, depending on the local wave action and weather, creating different textures, colors and gradients or layers of material.
Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landward retreat of the shoreline can be measured and described over a temporal scale of tides, seasons, and other short-term cyclic processes. Coastal erosion may be caused by hydraulic action, abrasion, impact and corrosion by wind and water, and other forces, natural or unnatural.
A bulkhead is a retaining wall, such as a bulkhead within a ship or a watershed retaining wall. It may also be used in mines to contain flooding.
Beach nourishment describes a process by which sediment, usually sand, lost through longshore drift or erosion is replaced from other sources. A wider beach can reduce storm damage to coastal structures by dissipating energy across the surf zone, protecting upland structures and infrastructure from storm surges, tsunamis and unusually high tides. Beach nourishment is typically part of a larger integrated coastal zone management aimed at coastal defense. Nourishment is typically a repetitive process since it does not remove the physical forces that cause erosion but simply mitigates their effects.
A seawall is a form of coastal defense constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a seawall is to protect areas of human habitation, conservation, and leisure activities from the action of tides, waves, or tsunamis. As a seawall is a static feature, it will conflict with the dynamic nature of the coast and impede the exchange of sediment between land and sea.
A breakwater is a permanent structure constructed at a coastal area to protect against tides, currents, waves, and storm surges. Breakwaters have been built since Antiquity to protect anchorages, helping isolate vessels from marine hazards such as wind-driven waves. A breakwater, also known in some contexts as a jetty or a Mole, may be connected to land or freestanding, and may contain a walkway or road for vehicle access.
A revetment in stream restoration, river engineering or coastal engineering is a facing of impact-resistant material applied to a bank or wall in order to absorb the energy of incoming water and protect it from erosion. River or coastal revetments are usually built to preserve the existing uses of the shoreline and to protect the slope.
Coastal geography is the study of the constantly changing region between the ocean and the land, incorporating both the physical geography and the human geography of the coast. It includes understanding coastal weathering processes, particularly wave action, sediment movement and weather, and the ways in which humans interact with the coast.
A gabion is a cage, cylinder or box filled with rocks, concrete, or sometimes sand and soil for use in civil engineering, road building, military applications and landscaping.
Coastal management is defence against flooding and erosion, and techniques that stop erosion to claim lands. Protection against rising sea levels in the 21st century is crucial, as sea level rise accelerates due to climate change. Changes in sea level damage beaches and coastal systems are expected to rise at an increasing rate, causing coastal sediments to be disturbed by tidal energy.
Swash, or forewash in geography, is a turbulent layer of water that washes up on the beach after an incoming wave has broken. The swash action can move beach materials up and down the beach, which results in the cross-shore sediment exchange. The time-scale of swash motion varies from seconds to minutes depending on the type of beach. Greater swash generally occurs on flatter beaches. The swash motion plays the primary role in the formation of morphological features and their changes in the swash zone. The swash action also plays an important role as one of the instantaneous processes in wider coastal morphodynamics.
Goleta Beach is a region of coastline located near Goleta, California, just east of the University of California, Santa Barbara (UCSB) campus. A portion of the shore of Goleta Bay is managed by the County of Santa Barbara, as the Goleta Beach County Park (GBCP). The beach itself is partly man-made as sand was spread onto an existing sandspit in 1945. The beach is a seasonal habitat for migrating shorebirds, including the snowy plover, an endangered species, and is occasionally closed due to nourishment efforts.
A tetrapod is a form of wave-dissipating concrete block used to prevent erosion caused by weather and longshore drift, primarily to enforce coastal structures such as seawalls and breakwaters. Tetrapods are made of concrete, and use a tetrahedral shape to dissipate the force of incoming waves by allowing water to flow around rather than against them, and to reduce displacement by interlocking.
Beach evolution occurs at the shoreline where sea, lake or river water is eroding the land. Beaches exist where sand accumulated from centuries-old, recurrent processes that erode rocky and sedimentary material into sand deposits. River deltas deposit silt from upriver, accreting at the river's outlet to extend lake or ocean shorelines. Catastrophic events such as tsunamis, hurricanes, and storm surges accelerate beach erosion.
The Gold Coast Shoreline Management Plan (GCSMP) is an ICZM plan to manage the coastal resources of City of Gold Coast. The EPA encourages the City Council's to produce shoreline management plans for coastlines and tidal waterways within the local authority area.
Hudson's equation, also known as Hudson formula, is an equation used by coastal engineers to calculate the minimum size of riprap (armourstone) required to provide satisfactory stability characteristics for rubble structures such as breakwaters under attack from storm wave conditions.
A honeycomb sea wall is a coastal defense structure that protects against strong waves and tides. It is constructed as a sloped wall of ceramic or concrete blocks with hexagonal holes on the slope, which makes it look like a honeycomb, hence the name of the unit. Its role is to capture sand and to discharge wave energy.
A coastal development hazard is something that affects the natural environment by human activities and products. As coasts become more developed, the vulnerability component of the equation increases as there is more value at risk to the hazard. The likelihood component of the equation also increases in terms of there being more value on the coast so a higher chance of hazardous situation occurring. Fundamentally humans create hazards with their presence. In a coastal example, erosion is a process that happens naturally on the Canterbury Bight as a part of the coastal geomorphology of the area and strong long shore currents. This process becomes a hazard when humans interact with that coastal environment by developing it and creating value in that area.
The Sea Bright–Monmouth Beach Seawall is a seawall located along the Jersey Shore in the Monmouth County, New Jersey towns of Sea Bright and Monmouth Beach. It roughly runs north-south direction along 4.7 miles (7.6 km) of the barrier spit of land along the lower Sandy Hook peninsula between the Atlantic Ocean and the Shrewsbury River estuary. The use of seawalls, groins, jetties, bulkheads, revetment, and beach nourishment since the late 1800s has made the stretch of coast one of the most heavily engineered sections of ocean shorefront in the world.
North Cove is an unincorporated community in Pacific County, Washington. North Cove is mostly residential, with some vacation rentals and a general store being the only commercial properties. The community suffers from the extreme coastal erosion of Cape Shoalwater, which has been diminished drastically in size, with the ocean claiming dozens of structures over the last 100 years and remaining a substantial threat.