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Barriers are elongated offshore ridges of sand (and gravel) that are separated from the mainland for most or all of their length. Spits are attached at one end to the mainland and usually develop where the coast changes direction. Barriers may elongate across the mouth of bays or lagoons and are then often referred to as bars. Storms may breach an attached spit, separating the barrier island from the mainland. The breach may then be maintained by the ebb and flow of tidal currents. Tombolos connect an offshore island with the adjacent mainland and are formed in the wave shadow of islands where the shore is protected from large waves. (Downing, 1983; Klee, 1999; Summerfield, 1991, Wright and Short 1984).
Dungeness Spit, Clallam County; Swantown, Thurston County; Fisherman’s Bay tombolo; Long Beach peninsula, Pacific County; Ocean Shores Peninsula, Grays Harbor County
Dungeness Spit, Clallam County
Bar:
Tombolos:
Longshore flow
Most barriers are maintained by sediment moved alongshore from an erosional source. If sediment movement is reduced or obstructed, erosion of the barrier may occur.
Cross-shore flow
Barriers may be overwashed or breached as a result of changes in sedment supply, large storms, and other factors. Overwashing is common mechanism of barrier migration.
Fluvial flow
Not a primary driving process for barriers.
Sediment
Longhore transport provides sediment so it should not be blocked by shoreline armoring such as bulkheads. Barrier might migrate so should plan for natural migrations.
Woody debris
Large logs, tree limbs and root wads that wash ashore on barriers can stabilize the landform by trapping sediment and deflecting cross-shore wave and wind flows. A reduction in inputs may therefore accelerate erosion and increase movement of the landform.
Non-point pollution
Because these landforms are partially or entirely detached from the mainland, they are less likely than estuaries, river mouths and deltas to trap pollutants from run-off and overland flows.
These dynamic systems are not suitable for development or armoring. To protect these systems, research of sediment movements at all spatial scales will help formulate the most appropriate management strategies.
Removal of hard structures that interrupt sediment transport to these landforms can help to restore landforms that have eroded as a result of sediment starvation. In situations where removal of such structures is not possible, artificial placement of sand and/or gravel on to the beach - sometimes referred to as "beach nourishment" can restore the barrier. If the natural sediment sources are permanently blocked, beach nourishment will have to occur with some regularity, depending upon the rate of erosion, to maintain the landform.
These landforms are sediment accumulations with a roughly triangular plan form, their apex extends outward into the marine water. They can be formed by converging wave directions off a shoal or point, from a recurved barrier spit or as a result of tidal/wave seasonal changes (Dolan et al., 1974; Downing, 1983)
West Point on Gedney Island, Snohomish County; Quatsap Point near Duckabush and Kala Point, Point Townsend, both in Jefferson County;
Gedney Island, Snohomish County
Longshore flow
Because these forms are the result of approximately equal bi-directional longshore flow, an interruption of longshore flow from either side of the cuspate foreland can dramatically alter its morphology. An abrupt increase in longshore flow energy from one direction can cause erosion on one side of the triangular form and deposition on the other, smoothing the point or creating a recurved spit. The point of a recurved spit can attach to the mainland, trapping water at the base of the original triangle.
Cross-shore flow
Increasing waves such as those create from boat wakes may cause overwash and erosion of the cuspate foreland.
Fluvial flow
Not a primary driving process for cuspate forelands.
Sediment
Decreasing sediments by armoring the sediment source or placing a groin or marina in the transport zone will starve the cuspate foreland of sediment, altering the morphology, perhaps even eliminating the landform.
Woody debris
A decrease in the supply of tree limbs and root wads that might potentially trap sediments and deflect cross-shore wave and wind flows may result in a less stable landform.
Non-Point pollution
This landform type does not tend to trap pollutants from overland flows.
Protect sediment sources and transport zones from shoreline armoring or construction of structures that may interrupt or impede the movement of sediment to the landform.
Remove structures that interrupt sediment transport or deflect wave/current energy and cause artificially high longshore flows.
These are mounds or ridges of loose, fine sand are heaped up by the wind blowing either seaward or shoreward. (Bird, 2000; Downing, 1983). The presence of dunes can protect beach backshores from flooding and storm damage.
Long Beach, Pacific County; Cranberry Lake on northwest Whidbey Island; Deception Pass State Park Point Wilson,
Long Beach, Pacific County Dunes 
Longshore flow
Reducing longshore flow will decrease sediment availability for building and maintaining dunes.
Cross-shore wind/wave flow
Increasing wind/wave energy affects dune morphology. Stable foredunes are common with low wind/wave energy situations while transverse dunes are found in high wind/wave energy conditions.
Fluvial flow
A decrease in fluvial flow can reduce deposition of fine sediments to the shore and consequently decrease the amount of fine sediments available for transport to the dunes by winds.
Sediment
Construction of riprap and bulkheads along unconsolidated sandy beaches may reduce sediments available for dune building.
Woody debris
Like vegetation on the dunes, woody debris can increase sand accretion and contribute to dune growth. Woody debris also serves as refuge for organisms living in the dunes.
Non-Point pollution
Increasing nutrients in the soil can effect dune vegetation distribution and abundance. Dunes are a natural filter for water, so destroying dunes will decrease water quality.
Protect dune vegetation and prohibit recreational activities that hasten erosion such as high use hiking and sand surfing.
Rebuild dunes by artificial placement of fine sand. Plant native dune grasses and vegetation to protect and stabilize
Return to list of shore typesAn area where
the mouth of a river enters marine waters and fresh and seawater
intermix. Estuaries are subdivided into three parts the upper (or
head) is the inland extent of marine tidal waters, the middle (or
main) is where full mixing occurs, and the lower estuary (or mouth) is
the seaward end or indentation of the coastline (Fairbridge,1980)
Examples:
Skagit River Estuary, Skagit county, Willapa Bay, Grays Harbor county, Quilcene Bay, Jefferson County
Skagit River Estuary, Skagit County
Longshore flow
Anthropogenic structures such as groins and jetties effect longshore transport which can change the morphology of the lower estuary. Shoreline armoring can also disrupt longshore sediment transport that supports the physical character and biological productivity of the upper intertidal habitat.
Cross-shore flow
Natural fluctuations and storms will inundate estuaries at different levels. Barriers that reduce the tidal prism may alter the morphology of the estuary and also the important habitat functions. Shoreline armoring can also increase wave energy and promote higher rates of erosion.
Fluvial flow
Altering fluvial inputs to an estuary by regulating flows upstream, can alter the stratification (salinity distribution) of an estuary, impacting its physical and biological processes. Flows may be affected by dams, land cover changes in the watershed, and stormwater diversions in suburban and urban watersheds.
Sediment
Freshwater flows during large floods are much greater than peak tidal flows. Thus, floods can transport sand downstream at very high rates, as evidenced by the substantial scouring of shallow sand shoals that tends to occur during floods. Increasing sediment inputs to the estuary can lead to filling in and ultimately shallowing of the estuary, changes to the substrate, and/ or increase turbidity, which may have impacts to the benthic ecology, and further consequences on species that feed on them, included listed fish.
Woody debris
Wood has a very limited influence on the overall morphology of an estuary except in situations where large jams cause channel shifting. Woody debris plays a primary habitat role of refuge cover.
Non-Point pollution
Estuaries tend to act as collect zones for non-point pollution. Increased soils from farms, construction sites, and logging areas can alter spawning sites as well as increase turbidity which reduces plant growth. Runoff containing fertilizers, livestock manure, pesticides, heavy metals, oil and other toxic chemicals can impact the biology of the estuary profoundly. Marinas and boat basins contribute untreated sewage, fish wastes, cleaning compounds, antifouling paints, as well as contaminated runoff from nearby parking lots. Impervious surfaces, associated with urban growth and industrial development provide a fast and direct route for polluted runoff whereas vegetated, undeveloped areas can slow runoff and filter contaminants.
Protect tidal inundations by restricting barriers. Limit encroachment by establishing buffers and protecting native riparian vegetation. Restrict shoreline armoring. Implement best management practices with new development in contributing basins.
Remove dikes and dams and shoreline armoring that interrupts flow of sediment and water. Restore native vegetation. Restore tidal sloughs. Reduce channelization. Implement best management practices when dredging to avoid or minimize impacts on benthic habitat and physical parameters of the estuary. Address failing septics.
Lagoons are shallow bodies of water, typically longer than they are wide, with very restricted exchange with the marine waters. There is minimal tidal flux and no significant freshwater inflow. Lagoons form where barriers or bars separate a section of water from open marine water (Klee 1999, Davis 1994).
Example:
Harrington Lagoon, Island County
Longshore flow
Longshore flows often provides sediment from updrift sources to barriers that form lagoons.
Cross-shore flow
Surging waves overtopping the bars separating lagoon water from the ocean are uncommon. Increasing wave energy could breach the barrier protecting the lagoon and alter its salinity regime which is typically driven seasonal fluctations in precipitation and evaporation. This would likely haveimpacts on the biology of the system.
Fluvial flow
Lagoons that form adjacent to stream mouths are often maintained by fluvial inputs of sediment. The deposited sediments are then moved by wave and littoral flows that form the bars. A restriction in this fluvial flow carrying sediment would result in a lack of sediment input to maintaining the bars, increasing the potential for breaching of the barrier to cross-shore waves.
Sediment
Modifications of lagoon inlet by placement of hard structures can deflect waves and alter longshore flows that move sediment and shape the barriers. Dredging activities can change the tidal prism, increasing marine inflows that can affect the benthic community.
Woody debris
The accumulation of large wood within lagoons may influence depth which could effect tidal prism and tidal dynamics.
Non-Point pollution
Closed lagoons are especially susceptible to non-point pollution by surrounding urban or agricultural activities.
Avoid modification of tidal inlets adjacent to lagoon. Limit new development of impervious surfaces in upland, updrift areas and protect riparian vegetation.
Restoration Opportunities:
Return to list of shore types
River deltas occur where rivers or streams deliver sediment to the coast faster than the sediment is removed. Deltas composed of sediment protrude out from the shoreline where rivers enter the marine water. The sediment is shaped into fans, channels and bars by fluvial flow, wave, tide and current action.
Examples:
Nooksack Delta, Whatcom County, Nisqually Delta, Thurston County
Nooksack Delta in Whatcom County
Longshore flow
Longshore transport can move sediment alongshore from the delta to create beaches downdrift. More exposed deltas are especially impacted by the reduction of longshore flow which reduces availability of the coarser materials that build bars and protect the delta.
Cross-shore flow
Natural fluctuations and storms will inundate the coasts at different levels. Barriers that reduce the tidal prism may alter the morphology of both tidal sloughs and distributaries. Shoreline armoring can also increase wave energy and promote higher rates of erosion. Dikes and levees prevent tidal flooding and sediment deposition on the delta surface, resulting in increased subsidence in diked and drained areas.
Fluvial flow
Rivers tend to transport high flows with minimum alteration to the primary physical characteristics of the channel and these flows will likely spread across the river valley rather than cause streambed scour. Changes to freshwater input affect position of saltwater wedge within estuarine deltas, possibly affecting habitat and/or physical processes of mixing and circulation.
Sediment
Decreasing sediment transport to the delta by installing dams upstream can decrease sediment deposition and can alter the sediment size and type, changing benthic habitat conditions. Where distributaries are channelized, sediment is no longer deposited across the delta marshes but is routed directly to river mouth and outer delta.
Woody debris
Removing woody debris decreases its primary habitat role as refuge cover. Woody debris may affect channel development by blocking distributaries.
Non-Point pollution
Upland vegetation reduces non-point pollution from entering the delta and negatively impacting the biological processes supported by the river delta. Most of the non-point pollution is associated with agricultural runoff from cultivated portions of delta and lower floodplain.
Allow unrestricted fluvial inputs of sediment by limiting construction of hard structures and dikes. Limit encroachment by establishing buffers and protecting native riparian vegetation.
Increase tidal influence by removing fill, breaching dikes, removing dikes. Reintroduce river flow into multiple distributaries to enhance sedimentation and delta marsh. Dike breaching enhances tidal inundation, but dike removal may be necessary to restore natural flooding and drainage patterns within marsh islands. Restoring natural river flows by removing upstream dams or changing dam operations. Widening or replacing a culvert to increase flushing and improve water quality. Maintaining sediment flow into the delta by limiting gravel removal in river channel. Re-planting native vegetation will help reduce pollution entering the water and provide nearshore habitat.
Like river deltas, stream mouths occur where steams or creeks intersect the marine coast however, protruding sediment features are not apparent because the stream water flow rates are lower and resulting in smaller volumes of fluvial sediment transported and deposited at the coastline.
Example:
Jod Creek on Vashon Island, King County
Longshore flow
Longshore flows transport sediment alongshore from the stream mouth to downdrift beaches at a rate equal to the input of sediment from in-channel flow.
Cross-shore flow
Cross-shore flows are not as important as longshore and fluvial flows in maintaining this landform.
Fluvial flow
Material is transported downstream by in-channel river and creek flow together with periodic overbank flooding caused by storms. Large sediment and debris is deposited out first into slower moving pools, finer material makes it way down to the stream mouth where it is then available to move alongshore with wave and currents. Freshwater inputs are important in maintaining the submerged vegetation often found near stream mouths that play a role in trapping sediment and stabilizing the landform.
Sediment
Because the volume present at stream and creek mouths is smaller than that found at river deltas, a relatively small change in sediment availability can significantly change the landform. Increasing a creek's sediment load by removing riparian vegetation, upland logging or development, could transform this stream mouth into a delta, increase bar formation, or cause reoccupation of relic channels. Decreasing the sediment supply could lead to bank erosion or downcutting. Anthropogenic structures such as groins and jetties that affect longshore currents can change the morphology and biology of the river mouth.
Woody debris
Large accumulations can cause the channel to shift. Deposition of materials in stream mouth may increase sediment trapping capacity at the mouth.
Non-Point pollution
Small stream and creek mouths are smaller than estuaries and river deltas and have longshore flows strong enough to transport materials away from the mouth so there is less trapping capacity for non-point pollution. However siltation from improper construction activities and runoff can lead to infilling.
Limit encroachment on stream banks by establishing buffers and
protecting native riparian vegetation.
Remove fill and flow restrictions to reintroduce natural conditions and freshwater input. Reduce channelization of lower stream to prevent loss of stream habitat, loss of aquatic productivity, increased stream bed and bank erosion, and a reduction of ground water levels.
Large sediment areas that develop in waters protected from waves where sediment is supplied from tidal currents or a nearby river. Sometimes tidal flats (also referred to as tidal fans) are pierced by tidal inlets - small indentations in the coastline with a relatively narrow channel or pocket of water that leads inland (Davies, 1980; Downing, 1983)
Longshore flow
A longshore flow that is great enough to support sediment transport to the landform but not so strong that it creates scour and erosion is important in supporting the physical character of tidal flats.
Cross-shore flow
Tidal flats tend to form in low wave environments, cross-shore flows tend to be low in areas where these landforms are present.
Fluvial flow
Sediment deposition from upstream flows are of primary significance in maintaining this landform. Reducing freshwater flow by upstream dams can alter the tidal flat morphology because of the changed sediment loads. Reduced flow, and consequently reduced erosive capacity, can result in greater incursion of marine-derived sediments (e.g. sands) into coastal waterways, causing expansion of flood tidal flats.
Sediment
Changes in tidal or fluvial sediment input will alter the morphology of the tidal flats and the substrate. An increase or decrease of sediment input will thus negatively impact the fauna and flora of the tidal flat.
Woody debris
Wood has a limited influence on the overall morphology tidal flats except in situations where large jams cause channel shifting.
Non-Point pollution
These landforms are subject to trapping increase nutrient inputs from upstream overland, subsurface, and hyporheic transport.
Particular attention should be paid to minimizing changes to sediment
transport from upstream sources and increasing inundation from
cross-shore flows. Hard shoreline structures such as bulkheads along
banks that provide sediment should be discouraged. Dikes and levees
prevent tidal flooding and sediment deposition on the tidal flats
surface, resulting in increased subsidence in diked and drained areas.
Wakes from large ship transport can increase cross-shore flow energy
causing increased inundation and erosion.
Restore tidal circulation by installing extra culverts under roads built across natural channels, remove dikes and levees that impede tidal flooding. Implement agriculture and stormwater best management practices to reduce run-off.
This classification consists of the shorelines that do not readily fit into the above depositional beach form types or the erosional types listed below. This shoreline type is quite variable, depending on the source of sediments, the composition of the sediment, slope, and both the cross-and longshore flows they experience. Nevertheless, though there is a range of sand-gravel beaches, they are more similar to each other than to the other types described.
Sand-gravel beaches are the accumulation of wave and current exposed sediment along the coast with the bulk of the substrate ranging from 0.2mm to 2.0mm. The beach face is the seaward edge where water runs up and down, its slope is determined by its composition material and exposure to wind and wave energy. Shoreward of the beach face, beach berms are sometimes formed from backwash deposition. Storm ridges are formed when storm waves of greater than average energy carry sediment further shoreward and deposit it higher up on the beach. Some beaches are composed of longshore bars and troughs seaward of the beach face that are visible only during low tide. This bar/trough system functions to store eroded sediment from the beach and transport it alongshore. Pocket beaches are found in small bays or alcoves that are protected by surrounding rocky cliffs and headlands. (Bird, 2000; Klee, 1999, Pethick, 1984)
Examples:
Countryside Beach, Eld Inlet Thurston County; Sunshine beach, Carr
Inlet, Pierce County; Luana Beach Maury Island King County; Pocket beach
on Hood Canal in Jefferson County
Pocket Beach, Hood Canal
Countryside beach (sand & gravel), Eld Inlet, Thurston County
Longshore flow
If the beach is located within a littoral drift transport zone, reduction in longshore flow may cause deposition and accretion of the beach. Conversely, an increase in longshore flow may result in erosion. Depending on the composition of native beach materials (mixture of coarse and fine sediments), runnels parallel to the shore may become evident.
Cross-shore flow
Periodic increased cross-shore flow may result in overtopping of the beach berm with finer material. Repeated or consistent increases in cross-shore flow may cause breaching of upper tidal storm ridge and the gradual formation of a lagoon.
Fluvial flow
Permeability is determined by substrate, therefore saturated sandy beaches will be more sensitive to erosion by increased freshwater inputs than rocky beaches will be.
Sediment
Bulkheads and reventments and other structures meant to stabilize unstable bluffs will reduce the sediment supply to downdrift beaches. Dredging can remove sediments from the system and increase beach erosion due to its effects in changing the wave energy in the dredged area. Groins and marinas built within the littoral sediment transport zone can also block sediments from depositing on the beach. Substrate composition can be altered by shoreline armoring effecting erosion rates and the biological community structure
Woody debris
Woody debris can stabilize beaches by providing protection from wave energy. However, beaches without berms can be negatively impacted by drift logs by scouring or damage due to movement of the logs by waves during high tide.
Non-Point pollution
These landforms are vulnerable to inputs of pollutants from hyporheic and overland transport. Because many of these sandy/gravel beaches are not in geologically hazardous areas, there has been and continues to be much residential development along these shorelines. They are often at risk to pollutants from degrading septics.
Protect feeder bluffs contributing sediments to the beach by
specifically including language in the Shoreline Master Program by
prohibiting construction of bulkheads, piers, or jetties in front of the
sediment source or in the transport zone. Maintain riparian vegetation,
particularly between urbanizing areas and the shoreline where vegetation
can provide the function of filtering nutrients and pollutants from
runoff.
Remove shoreline armoring that restricts transport of sediment to eroding beaches. Artificial beach nourishment for sediment starved or eroding beaches. Restore native vegetation.
Occur in areas where resistant rocks are present, (often as a result of cliff or platform weathering) and there is a lack of sediment input. In Puget Sound, rocky shores can occur in both high and fairly low energy settings. Shore rocks continue to weather as they are attacked by breaking waves that force air and water into fissures, eventually breaking the rocks further. Some coasts have irregular rocky shores, with intervening small bays that may contain sand or gravel beaches and there are dislodged blocks or boulders. These boulders have either been produced by weathering of rocky outcrops or are glacial erratics, that were delivered by former ice sheets. Many rocky shores originate from platform beaches that have been greatly dissected and grooved over time.
Examples: N. Cypress Island, Skagit county; West of Lake Ozette, Olympia National Park in Clallam county.
Northern end of Cypress Island, Skagit county
West of Lake Ozette, Olympia National Park in Clallam county.
Longshore flow
Along rocky shores, longshore littoral drift is generally not strong enough to transport rocks but can winnow away finer sediments, leaving the larger rocks behind.
Cross-shore flow
Cross-shore waves carrying rock fragments can cause abrasion on these rocky shores, producing pits, pools and cavities where rock material is removed. The runup of powerful storm waves can carry dense, large rocks and wood to the backshore and deposit this material where it remains inaccessible to fairweather waves and tides. This material may act as a trap for algae and kelp washed upshore in subsequent storms. The kelp, algae, woody mass will weather and rot over time, providing habitat for terrestrial and intertidal invertebrates.
Fluvial flow
Fluvial flow is not as significant as longshore and cross-shore processes in maintaining this land form.
Sediment
If the beach is located in an area that is not exposed to strong longshore or cross-shore flows, an increase in sediment availability may fill in crevices and pits, that provide important tidal pool habitat. Rocky beaches in higher energy settings are less responsive to changes to sediment availability. Sand tends to be transported away from these beaches, leaving the more resistant rock material behind.
Woody debris
Logs and tree limbs are often found piled up against large rocks or trapped between or behind rocks at the top of the beach on these shores. Unlike on sand-gravel beaches, large wood is less important in maintaining stability on rocky shores, but is significant in providing habitat. Wood that is held in place by its position among rocks is often the substrate that bivalves and barnacles settle on. The wood is slowly weathered, providing nutrients to surrounding tide pools. A reduction in woody debris may have significant impacts to the intertidal community on these shores.
Non-Point pollution
Rocky shores, where pollutant trapping sediment is scarce, and long and cross-shore flows are moderate to high, have relatively low sensitivity to changes in non-point pollution inputs.
Maintain riparian vegetation updrift of these shores that can provide
habitat forming woody debris.
If sediment inputs from upland or updrift sources has occurred as a
result of increased erosion, replanting of stabilizing vegetation can
reduce sediment infilling of rocky tide pools.
Steep sometimes vertical slopes that rise abruptly from the beach or platform. They are eroded by waves at the base though there are many factors involved in predicting the extent and rate of cliff erosion. These factors include but are not limited to the material composition and structure of the bluff itself, the beach fronting the bluff, and the long and cross-shore flows the bluff is subjected to (Emery and Kuhn, 1982; Komar 1998; Summerfield 1991; Trenhaile, 1987).
Examples:
Ebey's landing Whidbey Island, Island County; North of Cape Elizabeth,
Grays Harbor county; North Fort Warden State Park, Port Townsend,
Jefferson County
Ebey's Landing, Island County
North of Cape Elizabeth, Grays Harbor County
Longshore flow
Interruption of longshore flow will reduce erosion of the bluff which will decrease sediment transport to landforms down-current.
Cross-shore flow
Increasing cross-shore waves (wake surges by large ships for example), may increase erosion at the toe of the bluffs.
Fluvial flow
Not a primary driving process effecting bluffs.
Sediment
The erosion of coastal bluffs is a significant source of sediment for most beaches on Puget Sound. Bluff erosion is related to the width and height of the beach below it, so changes to longshore sediment supply may alter erosion rates. Building on cliffs can facilitate mass movements and increase the supply of coastal sediments. If a sediment source updrift of a steep, more resistant bluff is blocked, the sandy beach adjacent to and seaward of the bluff is likely to erode over time. The rocky headland or sea stack will promenade out into the water as a result. This may make a beach that was previously possible to walk along impassable.
Woody debris
Most bluffs along Puget Sound shorelines support large tree growth. Bluff erosion is therefore a significant source of deciduous and coniferous leaves, limbs and logs to beaches. The presence of large wood on the beach fronting a bluff may alter erosion patterns at the toe of bluffs by deflecting, absorbing and/or redirecting wave energy.
Non-Point pollution
Stormwater run-off , improper drainage (elephant trunks) and septics can also contribute to erosion and instability at tops of bluffs which may hasten slope failure.
Protect native vegetation. Define set-backs on unstable bluffs. Map
feeder bluffs and protect from improper development at the top and
bulkheading at the toe.
Remove bulkheads so that feeder bluffs can provide sediment to landforms down current. Revegetation of the bluff can reduce erosion, strengthen the soil and inhibit shallow landslides which all increase general slope stability. Reduce sources of runoff to the slope.
Dissection of promontories on a cliffed coast can leave small islets standing offshore, referred to as sea stacks. These can also result when a natural arch has collapsed. The orientation of the rock formation to the coast is an important factor in how the resulting landform will be configured. When rock strata are parallel to the coast, waves cut out caves and arches from the weaker less resistant material and seastacks form when more resistant portions of a cliff remain in the surf separated from the retreating cliff. When the rock strata are perpendicular to the coast and almost vertical, prominent headlands are formed where resistant rock (e.g. basalts) remain (Klee 1999; Emery and Kuhn, 1982; Komar 1998; Summerfield 1991; Trenhaile, 1987)
Examples: Sea stacks- Crying Lady Rock, Clallam county. Rocky headlands-Cape Flattery, Clallam county.
Crying Lady Rock, Clallam County
Cape Flattery, Clallam County
Longshore flow
The strength and direction of longshore flow is important to maintaining the shape of these landforms. A change in the orientation of longshore flow, resulting from updrift shoreline armoring (groins, jetties) may result in erosion of previously protected portions of the rock formation. Chunks of less resistant rock may be carved out, changing the shape of the feature, perhaps undermining the strength of arches and even causing collapse of caves.
Cross-shore flow
The shape of these landforms is strongly influenced by cross-shore flows. In many cases, the seaward sides of stacks are steeper than the landward side because they are exposed to stronger wave attack. The steepness of a headland will depend on the structure and resistance of the outcropping rock formation, and the degree to which it is weathered by marine erosion (waves ) versus precipitation and wind. In general, steeper headlands occur on costs exposed to strong wave action from large open sea fetch, and more subdued sloped headlands occur in relatively sheltered areas.
Fluvial flow
Not a primary driving process effecting sea stacks and rocky headlands.
Sediment
When sediment is available updrift of these rocky cliffs, pocket beaches between the resistant rock may develop.
Woody debris
These landforms are not particularly sensitive to changes in inputs of woody debris, though large logs can become trapped in crevices, arches and caves. These may enhance erosion if tossed about in storms and dislodge chunks of less resistant material. It is not uncommon for these landforms to have trees and other vegetation growing on them. The presence of this vegetation generally provides stabilization to the less resistant portions of the landform, though sometimes roots of trees can travel along a fissure and hasten infiltration of water along a bedding plane that destabilizes the formation, eventually causing it to beakaway and slide into the sea.
Some rocky headlands have groundwater seepages through the permeable portions of their formation. An increase in non-point stormwater runoff can lead to increased saturation and weakening of the landform.
Encourage setbacks from edge of rocky headlands. Implement BMPs for
stormwater runoff. Discourage development that obscures the view of
these often spectacularly attractive, unique landforms. Avoid shoreline
hardening that may deflect and reorient wave energy. Require new
bulkheads to incorporate “softer” bioengineering.
Restoration opportunities include retrofitting development with BMPs for stormwater shoreward of rocky headlands, particularly those known to have portions of permeable soils with groundwater seepages.
Gently sloping, relatively smooth, planar rock features that extend across the intertidal. These features can be formed in various ways. Some result from waves cutting into a rock cliff, often where the rock strata trend parallel to the coast and dip seaward. Quarrying and/or abrasion of uplifted terraces (or tectonically rising coasts ) by the surging motion of waves cause undercutting and rock slides occur along the bedding plane surface falling into the sea (Komar 1998; Trenhaile, 2002). Many platforms formed in this way have receding cliffs in their backshore. Others platforms, sometimes referred to as “structural platforms” are composed of resistant rock formations with surfaces coinciding with the shore. Shore platforms that are narrow (<10 m) are called benches and may be a micro outcrop of a much larger resistant rock formation. Structural platforms undergo dissection and weathering from waves and storm surges and grade into irregular rocky topography. Many rocky shores originate from planed platforms that have been greatly dissected and grooved over time.
Horizontal shore platforms that are submerged only briefly at significantly high tides are called “high tide platforms”. These are exposed during most of the tidal cycle to weathering processes from precipitation and drying rather than waves and tend to be smooth and bare. They are overwashed during storms and submerged by high spring tides. They typically end abruptly in a steep drop at the lower intertidal.
Examples:
Sucia Island, San Juan County
Southeast Sucia Island, San Juan County
Longshore flow
Depending on the direction of the rock strata with respect to the coast line, long shore flow from currents and deflected tidal surges can infiltrate along the bedding plane. With repeated exposure to this flow, huge hunks of the rock are eventually sliced off, leaving an unvegetated cliff surface that is fronted by an inclined rock surface that descends into the water.
Cross-shore flow
Waves and strong surging flows may undercut the rock strata resulting in abrupt slumps and rock slides. The remaining rock is often a steep, unvegetated scarp.
Fluvial flow
Not a primary driving process effecting platforms.
Sediment
Typically platform beaches are found in areas of strong waves and currents so sediment deposition is scarce. However an increase in sediment inputs from updrift and adjacent lands may result in a thin veneer of sand covering the rock platform, until seasonal or storm increases flow and transports the sediment downdrift from the platform.
Woody debris
These landforms are not particularly sensitive to changes in inputs of woody debris.
Non-Point pollution
These landforms do not have characteristics that make them very sensitive to inputs of non-point pollution. There is little sediment present to trap pollutants and high wave and longshore flow energy that would regularly flush the area.
Encourage setbacks along retreating cliffs fronted by platform beaches.
Because these cliffs are composed of rock, they often appear more stable
than they actually are. Drainage and runoff from residential development
at the top of cliffs contributes to the erosive forces of weathering and
water surges that can separate the rock along the strata.
Restoration opportunities are limited to retrofitting development with BMPs for stormwater on cliffs backing platform beaches.
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