1. Water Erosion and Deposition
Chapter 9
Water Erosion and Deposition

2. Surface Water
Runoff – rainwater that flows across Earth’s surface; amount of runoff is affected by several factors
Amount of rain that falls
Length of time the rain falls
Steepness of the slope, of the land
Amount of plants, vegetation

3. Surface Water Erosion – the wearing away of soil and rock by water
Rill erosion – during a heavy rain, a small stream forms and carries away soil, creating a groove called a channel.
Gully erosion – heavy rains remove large amounts of soil and sediment from a rill channel, forming a gully.

4. Surface Water
Sheet erosion – sheets of water flowing across the land pick up and carry away sediments
Stream erosion – water in a stream picks up sediments from the bottom and sides of its channel, making the channel deeper and wider

5. Surface Water
River system – the network of groundwater and streams that come together to form a river
Drainage Basin – the area of land from which a stream or river collects runoff
Mississippi River drainage basin – the largest in the United States

7. Surface Water Stages of stream development
Young streams – flow swiftly through a steep vally
May have whitewater rapids and waterfalls
Erodes the stream bottom faster than the sides

8. Surface Water Mature stream – flows more smoothly through its valley
Stages of stream development
Mature stream – flows more smoothly through its valley
Erodes more on its sides
Curves are called meanders
Carves a broad, flat valley floor called a floodplain

9. Surface Water Stages of stream development… continued
Old stream – flows slowly through a floodplain it has carved

10. Surface Water
Flooding – when too much water enters a river system, it overflows its banks
Dams – Built to control the flow of water downstream
Levees – mounds of earth built along the sides of a river to prevent flooding

11. Surface Water
Deposition – when water slows down, its drops, or deposits, the sediments it is carrying.
Delta – formed by sediments that are deposited as water empties into an ocean or lake
Alluvial fan – fan-shaped area formed by sediments deposited as water empties from a mountain valley onto a flat open plain

12. Groundwater
Groundwater – water that soaks into the ground and collects in the pores of the rock underlying the soil
14% of all freshwater exist as groundwater
Soil and rock are permeable if water can pass through the pore space. Example: sandstone
Soil and rock are impermeable if water cannot pass through them. Example: Granite

13. Groundwater
Aquifer – a layer of permeable rock that lets water move freely
Zone of saturation: the area where all pores in the rock are filled with water
Water Table – upper surface of the zone of saturation

14. Groundwater Water Table
Many people get their water from groundwater through wells
Groundwater flows into a well, and a pump brings it to the surface.
Good wells extend deep into the zone of saturation, past the water table.
Wells can dry up during seasons or if demand is too high

15. Groundwater Water table… continued
Artesian wells – water rises to the surface under pressure
Springs – the water table is so close to the surface that water flows out.
Geyser – a hot spring that erupts periodically, shooting water and steam into the air

16. Groundwater The work of groundwater
Groundwater mixes with carbon dioxide to form carbonic acid.
Acidic groundwater moves through cracks in limestone, dissolving the rock
Gradually, the cracks in the rock enlarge until a cave is formed

17. Groundwater
Stalactites – calcium carbonate deposit that hangs from the cave’s ceiling
Stalagmites – calcium carbonate deposit that forms on a cave’s floor

18. Groundwater The work of groundwater… continued
If underground rock is dissolved near the surface, a sinkhole forms

19. Groundwater
Subsidence – the sinking of land caused by the excessive withdrawal of groundwater

20. Ocean Shoreline
Shoreline forces – three major forces constantly change the shape of the shoreline.
Waves pound against shores, breaking rocks into smaller pieces
Move large amounts of sediments
Collide with the shore at angles, creating longshore currents, which act like rivers of sand in the ocean
Currents move sediments along the shoreline
Tides carry sediments out to sea and bring in new sediments

21. Ocean Shoreline Rocky shorelines – steep shorelines
Rocks and cliffs are the most common features
Softer rocks erode away before harder rocks, leaving islands of harder rocks

22. Ocean Shoreline Sandy beaches – gently sloping shorelines
Beaches – deposits of sediments that are parallel to the shore
Made of rock and shell fragments
Fragile because longshore currents constantly carry sand down the shore to form barrier islands, spits, sand-bars, and baymouth bars

23. Ocean Shoreline Sandy beaches… continued
Barrier islands – fragile sand deposits that parallel the shore but are separated from the mainland