Freeing the Elwha (Sediment Deposition at Sea)
OverviewAs rivers carry sediment to the sea different sediment structures are formed along shorelines, how is sediment important to both river and the shoreline ecosystems?
The focus of this lesson is depositional and erosional effects as rivers meet the sea. As a river meets the sea, the sediment it carries is deposited in a fan-like formation called a delta. As longshore drift picks up and transports the sediment, it can be carried and deposited down current to form shoreline sediment features such as sand bars, spits, and barrier islands. These sediments can protect areas behind them from the effect of ocean waves to form estuaries, salt marshes, and lagoons. Features such as headlands and sea stacks can intercept and deflect the currents, allowing sediments to be deposited on beaches in sheltered coves.
- Delta: As a river encounters a stagnant body of water, such as a lake or the ocean, the sediment load is deposited. The river will spread out across this delta into multiple channels, due to the meanders through this deposited sediment. Rivers with less sediment will form rounded fans (Nile), as the sea erodes its edges.
- Long shore drift:The movement of sediment down shore in a common direction caused by the combination of the ocean currents, wind direction, tidal movements, and oblique wave action on the shore.
- Beach:The zone above the water line at a shore of a body of water, marked by an accumulation of sand, stone, or gravel that has been deposited by the tide or waves.
- Spit: A long sandbar that heads far out into the ocean, formed by longshore drift. They often grow in length in the direction of the current and can form lagoons or salt marshes behind them.
- Sand bar: A strip of land formed by deposition of sediment via longshore drift or at the mouth of a river.
- Barrier Island:- A sandbar disconnected from the land. They form due to longshore drift and protect shallow brackish bays or salt marshes behind them. They general form in areas of low shore gradient.
- Lagoon: A shallow body of water, especially one separated from a sea by sandbars or coral reefs.
- Tombolo: A spit or sandbar which connects an island to the shore.
- Headland:An extension of land that juts into the sea from the coastline. Often it is made of materials resistant to erosion.
- Sea stack: An island of rock resistant to erosion, that is left behind, as the erosional action of the sea erodes into the surrounding material. They are often formerly connected to headlands.
- Ria:A flooded river valley from the ice age when sea level was lower (Grays Harbor or Chesapeake Bay)
- Cove: - A sheltered bay with headlands on two sides where sediment can be deposited.
- Lesson 5- Sediment Deposition at Sea.pptx
- Stream Table
- Reflection journal pages (printable handout)
- Vocabulary Notes (printable handout)
Review Essential Question and introduce Guiding Question.
Students should take a few minutes to respond to the reflection prompts. Discuss their answers and any questions they've generated.
Hand out Vocabulary Notes. Review the words. Students along with teacher can define words as they watch the PowerPoint Lesson.
Present PowerPoint Lesson.
Run Demonstration on Stream Table of a low-gradient mature river entering stagnant water. Show features such as braiding, delta formation, and longshore drift.
Hand out the second Reflection Journal Page. Give students time for a final reflection on the lesson.
Additional ResourcesBarrier Island
Long shore drift