Tidal scour is "sea-floor

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

caused by strong tidal currents resulting in the removal of inshore sediments and formation of deep holes and channels". Examples of this hydrological process can be found globally. Two locations in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

where tidal scour is the predominant shaping force is the

San Francisco Bay San Francisco Bay (Chochenyo language, Chochenyo: 'ommu) is a large tidal estuary in the United States, U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the cities of San Francisco, California, San ...

and the Elkhorn Slough.Silberstein 1989 M, Campbell E. 1989. Elkhorn Slough. Monterey, CA: Monterey Bay Aquarium. 64 p. Tidal force can also contribute to bridge scour.

Historical Perspective and Relevance

Research on tidal scour is largely centered at Elkhorn Slough in California. The slough was directly exposed to tidal flux beginning in 1947 with the creation of the Moss Landing Harbor. Multiple studies have been done on the slough since tidal exposure to catalog the morphological change and determine how long it will take for the system to reach equilibrium. Moss Landing California aerial view

Formation

Tidal scours are formed in tide-dominated

deltas A river delta is a landform, wikt:archetype#Noun, archetypically triangular, created by the deposition (geology), deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or ...

and

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

with the changing of the tide. As the tide changes from low to high or high to low, water is transported through the channel taking sediment with it. With increasing erosion, there is increasing tidal volume creating a self-perpetuating system. Tidal scour is most apparent when a barrier is breached due to natural or

anthropogenic Anthropogenic ("human" + "generating") is an adjective that may refer to: * Anthropogeny, the study of the origins of humanity Anthropogenic may also refer to things that have been generated by humans, as follows: * Human impact on the enviro ...

forcing.

Anatomy

Bathymetry

Tidal scour can be determined by looking at the change in

bathymetry Bathymetry (; ) is the study of underwater depth of ocean floors ('' seabed topography''), river floors, or lake floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of wate ...

over time. Bathymetry of tidal channels is determined using multi-beam sonar or

LiDAR Lidar (, also LIDAR, an acronym of "light detection and ranging" or "laser imaging, detection, and ranging") is a method for determining ranging, ranges by targeting an object or a surface with a laser and measuring the time for the reflected li ...

. By comparing cross-sections of channel bathymetry over several years and at various distances in the tidal channel, the amount of tidal scour can be quantified.

Grain Size Distribution

Sediment grab samples show that in areas demonstrating tidal scour, there is an increase in

grain size Grain size (or particle size) is the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which ...

from surrounding areas.

Ecological Significance

With direct influence from the Ocean, slough

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

can change significantly making it difficult for native species to persist. This can be seen in: *Increased transport of agricultural runoff, such as DDT-laden sediment, introduced by increased tidal scour. (''dead link'') *The erosion of marshes and eelgrass beds. *The loss of benthic organisms as the channels deepen more than organisms can persist.

References

{{Reflist Geological processes Geology Geomorphology