Water Erosion and Deposition

Surface Water

8.1

I. RunoffA. Runoff – water that doesn’t soak into the

ground or evaporate.

B. Factors Affecting Runoffa. Amount of Rain

i. Light rain has time to soak in.

b. Length of Time

c. Slope of Landi. On steep slopes, gravity causes water to runoff

before it can soak in or evaporate.

d. Amount of Vegetationi. Water will runoff areas with little or no vegetation.

C. The Effects of Gravitya. Water falling down a slope picks up speed,

and causes erosion much quicker than slow-moving water.

D. Water Erosiona. Water will wear a path as it travels down a

slope time after time.

E. Rill and Gully Erosiona. Rill Erosion – small stream erodes plants

and soils and leaves a small scar.

b. Gully Erosion – a rill channel that becomes broader and deeper to form a gully

F. Sheet Erosiona. Sheet Erosion – rainwater flows into lower

elevations, carrying sediments with it.

G. Stream Erosiona. Water can continue to flow in low elevations,

carrying sediments, causing erosion.

II. River System DevelopmentA. River System

a. Water runoff joins small streams, and larger streams form.

b. When larger streams join together they form rivers.

B. Drainage Basinsa. Drainage Basins – Land area from which a

stream gets its water.

b. All water in a river system eventually flows to the same location

c. The largest drainage basin in the US is the Mississippi River drainage basin.

III. Stages of Stream DevelopmentA. Rivers are classified as young, mature ,

or old.

B. Classification is based on movement, not on actual age.

C. Young Streamsa. Flow down steep slopesb. May have waterfalls, and whitewater rapidsc. Has high energy and erodes the stream

bottom more than its sides.

D. Mature Streamsa. Flows less swiftlyb. Most of the rocks that cause waterfalls and

rapids have been eroded away.c. Erodes more on the sidesd. Forms curves because the speeds of the

water changes.e. Shallow water moves slowly due to frictionf. Meander – curves formed by faster moving

water.

g. Floodplain – broad, flat valley floor carved by a meandering stream

E. Old Streamsa. Flows slowly through a broad, flat floodplain

F. Too Much Watera. Rivers can overflow over their banks

b. Dams and levees are built to stop flooding

IV. Deposition by Surface WaterA. When water looses energy it will drop

sediments.B. Delta – triangular or fan-shaped deposit

formed as sediments are deposited as water empties into an ocean, gulf, or lake.

C. Alluvial fan – deposit created when water empties from a mountain valley onto a flat open plain.

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Water Erosion and Deposition

8.2

Groundwater

I. Groundwater System DevelopmentA. Soil is made of many small rock

fragments, with weathered rock underneath.

B. Space between the fragments and pieces of weathered rock are called pores.

C. Groundwater – water that soaks into the ground and collects in pores.

D. Permeabilitya. Groundwater system is similar to a river

system.

b. Water travels via connected pores.

c. Permeable – water is able to pass through pores

i. Sandstone is permeable

d. Impermeable – water cannot pass throughi. Clay is impermeable

E. Groundwater Movementa. Groundwater will continue going down until it

reaches an impermeable layer.

b. It will then fill up all of the open pores in the permeable layer above.

c. Aquifer – layer of permeable rock that lets water move freely.

d. Water table – upper surface of the zone of saturation.

II. Water TableA. Average person uses 80-100 gallons of

water per day.

B. Wellsa. Goes deep into the zone of saturation

b. Pumps bring it to the surface

c. If the water table drops, because of a dry season, then a well can go dry

d. Rainfall or an increase in groundwater is needed to raise the water table

e. Too much water being pumped can lead to land sink

f. Artisan well is a well that does not require a pump.

i. Sloping aquifer forces water to rise from pressure

ii. Less common than other wells

C. Springsa. Spring – where the water table meets the

Earth’s surface and flows out.

b. Used as a source of fresh water

c. Can be hot when rocks in contact with the water are heated by the molten material under the surface.

D. Geysersa. Geyser – hot spring that erupts periodically,

shooting water and steam into the air.

b. Groundwater is heated causing it to expand

c. Remaining water boils quickly turning into steam.

d. Steam erupts forcing the remaining water out with it.

III. Groundwater Erosion and DepositionA. Water mixes with CO2 to create a weak

acid.

B. Acid can dissolve rock, specifically limestone.

C. Cave – cracks in limestone are enlarged until an underground opening is formed.

D. Cave Formationa. Stalactites form when water evaporates from

the ceiling of a cave leaving behind a deposit of calcite.

E. Sinkholesa. Forms when underground rock is dissolved

near the surface.

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Water Erosion and Deposition

8.3

Ocean Shoreline

I. The ShoreA. Shoreline is where the land meets the

ocean.

B. Shoreline Forces a. Surface waves and tides move sediments

back and forth, constantly eroding and depositing sediments.

b. Longshore current – water current that runs parallel to the shore, along the beach

i. Carries metric tons of sediment and acts like rivers of sand in the ocean.

ii. Uses extra energy to erode more shoreline sediments.

II. Rocky ShorelinesA. Waves wear around rock to form

hollows and eventually caves.

B. When too much erosion occurs, overhanging rock may fall into the ocean.

C. Rock fragments are ground up by the endless motion of waves and transported as sediment by the longshore current.

D. Soft rocks are eroded before harder rocks leaving islands of harder rocks.

III. Sandy BeachesA. Beaches – deposits of sediments that

run parallel to the shore

B. They stretch inland as far as tides and waves can deposit sediment

C. Made of many different materialsa. Pebbles, sand, and seashells

b. Quartz

c. Hawaii’s black sands – basalt

d. Green sands – olivine

e. Jamaica's white sands – coral and shell fragments

IV. Sand Erosion and DepositionA. Eroded by longshore currents, wind, and

storms.

B. Easily damaged by storms and human activities

C. Barrier Islandsa. Barrier Islands – sand deposits that parallel

but are separated by the mainland

b. Start underwater, and are added to by hurricanes and storms.

c. Once exposed, wind blows loose sand into dunes.

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