Longshore drifts and longshore currents

After today, I will start posting on a weekly basis every Saturday. I will also include urls of the websites which I get my information from. I've been a little lazy recently, so this post would be on something I've learned in secondary school, hope it would be useful.


Waves and currents causes transportation of sediments in the coastline (the place where the land and sea meets and interacts) Longshore currents and longshore drifts are terms we need to know regarding this topic. They can be a little confusing.

Longshore currents are flows of water that move parallel to the coast. It is generated by winds, tides and waves that approaches the coast at an angle driving the flow of water along the length of the coastline. Very specifically, it is defined as such... ''the longshore current is the dominating current in the nearshore zone. It is running parallel to the shore. The longshore current is generated by the shore-parallel component of the stresses associated with the breaking process of obliquely incoming waves, the so-called radiation stresses, and by the surplus water which is carried across the breaker zone across the coastline.''


Longshore drift on the other hand refers to the movement of sediments along the coastline. How it occurs is simple. When waves approach the coast at an angle due to wind direction, it carries sediments to the coast at an angle. However gravity only causes the sediments to move downwards perpendicularly to the coastline thus the sediments would travel along the coastline in a zig-zag motion when it is repeatedly carried at an angle and returned vertically downwards. Note: Sediments are carried to the coast when a wave crashes onto the coast, know as a swash. The motion where the seawater retreats back into the sea is known as a backwash. The backwards motion that pulls the sediments back. Longshore currents may result in longshore drift. This is illustrated below: (due to the fact that my 2 mega pixel camera was horrible at taking good photographs and that I could not operate my new scanner I could not draw out the diagrams for use)  

I do not own this photograph check links below credits go to the website

The world's longest naturally occurring spit, the 'Dungeness Spit' is found in America. Spits are one type of coastal landform that we see, along with cliffs, beaches, bays just to name a few. It is a result when longshore currents that transport sediments in the sea encounters a place of shallow sheltered water, enabling the sediments to be deposited in those regions. The accumulation of these sediments along the direction of the long shore current creates a narrow ridge of sand we identify as a spit. 

I do not own this as well. Check links below credits go to the website

Stuff about longshore drift: From my textbook
Photo of spit: http://tidelineconsultingllc.com/
Longshore current definition: http://www.coastalwiki.org/coastalwiki/Longshore_current
More about longshore current: http://www.usoceansafety.com/safety/popup/lscurrent.asp
Photo on longshore drift:   http://cgz.e2bn.net/e2bn/leas/c99/schools/cgz/accounts/staff/rchambers/GeoBytes/GCSE%20Revision/Glossaries/Glossaries/Glossary%20Extra%20Page%20Links/LongshoreDrift1.gif