Beaches

Marine Beaches
Beaches are relatively level land areas which are contiguous with the water and are directly affected by marine waters even to the point of origination. The most common types of beaches in Washington marine waters are sandy and rocky.

Sandy Beaches
Waves, wind, tide, and geological material are the principal factors involved in the formation of beaches. The beach material can usually be traced to one of four possible sources: the cliffs behind the beach; from the land via rivers; offshore wind; and finally from long shore-drifting of material. Long shore-drifting material must have been derived initially from the first three sources. Most beach material in Puget Sound is eroded from the adjacent bluffs composed of glacial till.

The effect of wave action on the movement and deposition of beach material varies depending upon the size of the material. Hence, in most cases, beaches composed of different sized material are usually characterized by different slopes and profiles. The entire process of beach formation is a dynamic process resulting from the effect of wave action on material transport and deposition. Initially, wave action will establish currents which transport and deposit material in various patterns. However, once a particular beach form and profile is established, it begins to modify the effects of waves thus altering the initial patterns of material transport and deposition. Hence, in building beach structures such as groins, bulkheads, or jetties, it is particularly important to recognize that subsequent changes in wave and current patterns will result in a series of changes in beach formation over time (see Use Activity Policies and Regulations).

Beach Formation
In the process of beach formation, sand particles are transported up the beach by breaking waves that wash onto the beach in a diagonal direction and retreat in a vertical direction. At the same time, long shore currents are created in the submerged intertidal area by the force of diagonally approaching waves. Beach material suspended by the force of the breaking waves is transported in one direction or another by the long shore current. Long shore-drifting of material often results in the net transportation of beach material in one direction causing the loss of material in some areas and gains in others.

The profile of a beach at any time will be determined by the wave conditions during the preceding period. Severe storms will erode or scour much material away from the beaches due to the force of retreating waves. During calm weather, however, the waves will constructively move material back onto the beach. This destructive and constructive action, called cut and fill, is evidenced by the presence of beach ridges or berms. New ridges are built up in front of those that survive storm conditions as sand is supplied to the beach in succeeding phases of calmer weather. In time, the more stable landward ridges are colonized by successional stages of vegetation. The vegetation stabilizes the ridges, protects them from erosion, and promotes the development of soil.

Rocky Beaches
Rocky beaches, composed of cobbles, boulders, and/or exposed bedrock are usually steeper and more stable than sandy shores. Coarse material is very permeable which allows attacking waves to sink into the beach causing the backwash to be reduced correspondingly. On sandy shores a strong backwash distributes sand more evenly, thus creating a flatter slope.

On rocky shores a zonal pattern in the distribution of plants and animals is more evident than on muddy or sandy shores. The upper beach zone is frequently very dry, limiting inhabitants to species which can tolerate a dry environment.

Intertidal Zone
The intertidal zone is a narrow area between mean low tide and mean high tide that experiences uninterrupted covering and uncovering by tidal action. One of the major characteristics of this zone is the occurrence of tidal pools which harbor separate communities which can be considered subzones within the intertidal zone.

Subtidal Zone
The subtidal zone is characterized by less stressful tidal influences but is subject to the forces of waves and currents which affect the distribution and kinds of organisms in this zone.