tidal scour
{{Short description|Sea-floor erosion caused by strong tidal currents}}
Tidal scour is "sea-floor erosion caused by strong tidal currents resulting in the removal of inshore sediments and formation of deep holes and channels".{{Cite book|title = McGraw Hill dictionary of scientific and technical terms|last = Parker|first = Sybil|publisher = McGraw-Hill|year = 1994|isbn = 978-0-07-113584-9|location = New York}} Examples of this hydrological process can be found globally.{{Cite thesis|last = Dean|first = Edwin Wendell|date = 2003|title = Tidal Scour in Elkhorn Slough, California: A Bathymetric Analysis|type=BS capstone project|publisher = California State University, Monterey Bay|url = http://seafloor.otterlabs.org/publications/SFML_Capstones/Dean_capstone03.pdf|accessdate = 15 December 2019|via = Seafloor Mapping Lab, CSU Monterey Bay}}{{better source needed|date=April 2023}}{{Cite journal|url = https://www.researchgate.net/publication/223927351|title = The Opening of Cook Strait: Interglacial tidal scour and aligning basins at a subduction to transform plate edge|last1 = Lewis|first1 = Keith|date = 1994|journal = Marine Geology|volume = 116|issue = 3–4|pages = 293–312|doi = 10.1016/0025-3227(94)90047-7|access-date = 15 December 2019|last2 = Carter|first2 = Lionel|last3 = Davey|first3 = Fred|bibcode = 1994MGeol.116..293L}}{{Cite journal|title = Anatomy of the tidal scour system at Minas Passage, Bay of Fundy, Canada|last1 = Shaw|first1 = John|date = 2012|journal = Marine Geology|volume = 323-325|pages = 123–134|doi = 10.1016/j.margeo.2012.07.007|last2 = Todd|first2 = Brian|last3 = Li|first3 = Michael|last4 = Wu|first4 = Yongsheng|bibcode = 2012MGeol.323..123S}} Two locations in the United States where tidal scour is the predominant shaping force is the San Francisco Bay and the Elkhorn Slough.{{better source needed|date=April 2023}}{{Cite thesis|last = Malzonen|first = Christopher Mario|date = 1999|title = Tidal scour and its relation to erosion and sediment transport in Elkhorn Slough|type=MS thesis|publisher=San Jose State University|url = http://scholarworks.sjsu.edu/etd_theses/1826/|accessdate = 15 December 2019|doi = 10.31979/etd.zz9e-ww37|doi-access = free}}Silberstein 1989 M, Campbell E. 1989. Elkhorn Slough. Monterey, CA: Monterey Bay Aquarium. 64 p. Tidal force can also contribute to bridge scour.{{better source needed|date=April 2023}}
Historical Perspective and Relevance
Research on tidal scour is largely centered at Elkhorn Slough in California.{{better source needed|date=April 2023}} The slough was directly exposed to tidal flux beginning in 1947 with the creation of the Moss Landing Harbor.{{better source needed|date=April 2023}} 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.{{better source needed|date=April 2023}}
Formation
Tidal scours are formed in tide-dominated deltas and estuaries 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.{{better source needed|date=April 2023}} Tidal scour is most apparent when a barrier is breached due to natural or anthropogenic forcing.{{better source needed|date=April 2023}}
Anatomy
= Bathymetry =
Tidal scour can be determined by looking at the change in bathymetry over time. Bathymetry of tidal channels is determined using multi-beam sonar or LiDAR. 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.{{better source needed|date=April 2023}}{{Cite journal|title = Character, distribution, and ecological significance of storm wave-induced scour in Rhode Island Sound, USA|last1 = McMullen|first1 = Katherine|date = 2015|journal = Geo-Marine Letters|volume = 35|issue = 2|pages = 135–144|doi = 10.1007/s00367-014-0392-0|last2 = Poppe|first2 = Lawrence|last3 = Parker|first3 = Castle|bibcode = 2015GML....35..135M|hdl = 1912/7246|s2cid = 53695218|hdl-access = free}}
= Grain Size Distribution =
Sediment grab samples show that in areas demonstrating tidal scour, there is an increase in grain size from surrounding areas.
Ecological Significance
With direct influence from the Ocean, slough morphology can change significantly making it difficult for native species to persist.{{better source needed|date=April 2023}} This can be seen in:
- Increased transport of agricultural runoff, such as DDT-laden sediment, introduced by increased tidal scour.{{Cite web|url = http://www.elkhornslough.org/sloughlife/birds/caspian_tern.htm|title = Caspian terns: the world's biggest tern nests at Elkhorn Slough!|date = 2001|accessdate = 15 December 2019|website = Elkhorn Slough National Estuarine Research Reserve (ESNERR)|archive-date = 26 August 2018|archive-url = https://web.archive.org/web/20180826124413/http://www.elkhornslough.org/sloughlife/birds/caspian_tern.htm|url-status = dead}} (dead link)
- The erosion of marshes and eelgrass beds.{{better source needed|date=April 2023}}
- The loss of benthic organisms as the channels deepen more than organisms can persist.
See also
- {{annotated link|Bridge scour}}
- {{annotated link|River delta}}
- {{annotated link|Estuary}}
- {{annotated link|Sediment transport}}