In this EarthCache, you will be observing longshore transportation of the beach sands on Venice Beach and the unique way the breakwater affects the normal transportation of sand. You will take a picture of the breakwater, pace off various distances, and post your measurements in your log to provide a public running documentation of the conditions in the area. Privately, you will send me your description of what occurred on the day you visited this Earthcache.
Longshore transport is the movement of sediment along coastlines driven by waves and currents. When waves approach the shore at an angle, they create a longshore current that moves sand parallel to the coastline.
Key Concepts of Longshore Transport
- Longshore transport is defined as the movement of sand and sediment parallel to the coastline.
- Wave Action: Longshore transport primarily occurs by waves approaching the shore at an angle.
- Longshore Current: As waves break on the shore, they generate a longshore current that flows parallel to the coastline facilitating transport of sand and other materials. This current is essential for transporting sediments over long distances along the beach. The primary force driving longshore transport is the swash (the movement of water up the beach) and backwash (the water retreating to the ocean).
- Coastal Features Formation: The movement of sand creates various coastal features, including beaches, dunes, and barrier islands, which play critical roles in coastal ecosystems and human activities.
- Human Impact and Management: The Corps of Engineers has installed jetties on many of the beaches in Southern California. The purpose of these jetties is to slow the process of longshore transportation to ensure wide beaches for recreational use.
In summary, longshore transport is a fundamental process that influences coastal dynamics, contributing to the formation of various coastal features and requiring careful management to mitigate human impacts.
Logging requirements: Included items 1 – 4 in your log to provide a public running documentation of the conditions at the breakwater. Privately, message me your answer to item 5. There are no right or wrong answers. These are your observations and opinions.
- Take a picture that includes the entire length of the breakwater from your Point B and Point C.
- Use this link, Santa Monica Tides ,and post the current tide.
- Is the beach cut back more on the upcoast side or the downcoast side?
- Get as close to the breakwater as you can and estimate these measurements. For reference, the breakwater is approximately 500 feet long
- How close can you get to the breakwater?
- Pace off the distance from Point B to Point C and estimate the distance in feet.
- Approximate the distance from Point A to Point B and from Point C to Point D
Message me this information:
- Based on your measurements and observations, describe the current longshore transport and how the breakwater is affecting it. Things you may observe:
- The height and direction of the waves
- Is water flowing between the sand spit and the breakwater? If so, which direction and how fast.
- Is sand accumulating or being washed away on the upcoast and downcoast side of the breakwater?