Image source: Wikpedia
Sandy beaches are highly dynamic environments subject to rapid, extreme changes. Typically located on passive margins, in areas characterized by low-wave energy, a wide continental shelf, and high offshore sediment influence, sandy beaches are found in wave-dominated, depositional settings such as the Atlantic Ocean and Gulf of Mexico coasts. Depositional settings along sandy coasts produce barrier structures such as bay barriers, barrier spits, and barrier islands. Coastal barriers are highly complex and dynamic landforms that experience constant change and movement. These narrow strips of sand serve as obstacles to wave activity, protecting fragile environments that lay further inland, for example, marshes, tidal flats, and lagoons. (National Parks Service)
The overall significance of sediment transport depends on whether it occurs along coasts of free or impeded transport. Impeded transport is characteristic of coasts with irregular configurations. The amount of sediment transport is limited by the trapping of sediment against headlands or coastal engineering structures. This contrasts with unimpeded sediment transport along straight coasts. Determined by the particular coastal configuration, the rate of longshore transport will be related to the predominant angle of the wave approach and the constancy and velocity of longshore currents. When these factors are high, an increase in sediment mobilization and transport will exist. When the velocity of flow is low, sediment settles and builds up. The movement of sediment in dynamic barrier island systems is described by a sediment budget. Sediment is moved between islands via currents. Material taken from one location is deposited elsewhere in an ever shifting system of sandy coastal landforms. (National Parks Service)
An estuary is an area where a freshwater river or stream meets the ocean. Water continually circulates into and out of an estuary. Tides create the largest flow of saltwater, while river mouths create the largest flow of freshwater. When dense, salty seawater flows into an estuary, it has an estuarine current. High tides can create estuarine currents. Saltwater is heavier than freshwater, so estuarine currents sink and move near the bottom of the estuary. When less-dense freshwater from a river flows into the estuary, it has an anti-estuarine current. Anti-estuarine currents are strongest near the surface of the water. Heated by the sun, anti-estuarine currents are much warmer than estuarine currents. (National Geographic)
The California Current moves southward along the coast of North America. However, in the Southern California area, it makes a little u-turn and flows northward, forming the Southern California Eddy/Countercurrent. (Wikpedia) Oceanside is one of the areas caught in this against-the-grain current flow, which impacts the unique current and sediment situation you'll see at GZ.
GZ can be observed from many different angles. You can answer the following questions from on top of the bridge, down on the beach, or even in the water. All up to you!
1. What forms of sand do you see? (sediment buildup, sediment transport, coastal landforms, strips of sand, etc.)
2. Do you see any evidence of impeded sand transport? What does it look like?
3. What directions are the currents flowing in? (towards the ocean, away from the ocean, etc.) Do you see signs of estuarine and anti-estuarine currents?
4. How have the currents affected the sand? (Hint: how has the strength of the currents moved or carved out the sand?)