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Chapter 13 Surface Water

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stacie stonebraker

on 9 May 2016

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Transcript of Chapter 13 Surface Water

13.I Streams and Rivers – carry over half of all water that falls on Earth’s surface to the ocean and cause almost all erosion.

13.2 .Stream Erosion and Deposition
12.3 River Valleys
13.4. Flood plains and Floods
A.River Systems
1. Tributary – stream that runs into a large stream
e.g. Beaver is a tributary of the Ohio
Running water is the most effective agent of erosion.
Flood – when a river overflows it banks the part of the valley floor it covers is the flood plain
Chapter 13 Surface Water
2.River System – a river and all of its tributaries
3.Drainage Basin (watershed) – includes all the land that drains into the river
4. Divide – highland that separates one drainage basin from another
e.g. Rocky Mountains – the major Western divide for the Mississippi river. Rain falling on the Eastern side flows to the Mississippi on the Western side to the Pacific.
B. Characteristics of Streams and Rivers – is controlled by velocity, gradient and shape of channel
1. Velocity – distance the water travels in a given amount of time
a. Faster it moves the more material it can carry and the larger the size of the material
b. Controlling factors of velocity: steepness of slope, amount of water traveling downstream, the shape of the stream channel
2. Gradient – steepness of the slope of a stream
3. Discharge – the amount (volume) of water that passes a certain point in a given amount of time
a. The more streams that feed the stream the higher the discharge (downstream)
b. Rain and melting snow may also add to discharge increasing the streams velocity
4. Channel – the path the water flows
a. A wide winding channel will slow the water down due to friction
b. A straighter deeper channel will have less friction therefore a higher velocity
A. How streams weather and erode material
1. Rapidly flowing water can lift, split off and move rock
2. Abrasion is the most effective form of erosion. The stream uses sand, pebbles and boulders as cutting tools.
a. The cut banks and beds of rivers and round themselves in doing so
b. Potholes – sand pebbles and boulders swirl in whirlpools grinding out a hole in the streams bed.
-limestone and marble most easily eroded by rock
B. How streams transport material
1. Load – soil and rock material being transported by the stream
a. Solution (dissolved load) – most comes from groundwater entering the stream
b. Suspension – turbulence keeps material supported in water – cause the water to look muddy
c. Bed load – material that is too heavy to be carried in solution travels on the floor (bed)
2. Competence – is a measure that describes the maximum size of the particle a stream can carry
3. Capacity – is a measure of the total amount of sediment a stream can carry
-velocity controls both the higher the velocity the larger the competency
4. During floods sand and pebbles can be carried in suspension this when most of the streams erosion is done
C. Stream Deposition
1. Deposition (dropping of load) occurs in a stream when its velocity or discharge is decreased
2. The greatest decrease in a rivers velocity occurs when it empties into a sea or lake. All sediment will deposited
D. Depositional features
1. Delta fan shaped deposit that forms when a river flows into a quiet or large body of water

a. Small current and waves along with a large amount of sediment helps deltas to form

b. Distributaries – branches in the delta that distributes sediment
2. Alluvial fan – form at the base of a steep hill in a dry region
begins as a gulley which grow in length, width and depth every time it rains
when it cuts deep enough to hit the ground water it becomes a stream
headward erosion – stream lengthens above its headwater
A. Canyons and v-shaped valleys
1. Canyons form – when the river cuts into its bed rapidly or when the rock materials on the side of the canyon are resistant to erosion.

a.Rock type will affect the speed of cutting also
2. V-shaped valleys describe youthful valleys
a.No large bends will exist
b.V-shaped comes from the exposed walls being eroded by longer amount of time
3. Base level – lowest level a stream can erode to
a.Controlled by what the stream flows into
b.Closer to base level the lower the gradient and sideways erosion occurs
4. Stream Piracy – through headward erosion, one river wears through the divide and captures the headwaters of the other river
B. Rapids and Waterfalls
1. Rapids are formed by the recession of waterfalls
2.Waterfalls are reduced by undermining
- undercut the waterfall which eventually falls
A.Features of a Flood plain
1. Reasons why a river near base level meanders (bends)
a. River current is more easily deflected because of a lower velocity
b. Erosion is more dominant on the outside of the bend
2. Oxbow lake – curved body of water formed when the river cuts off a bend
3. Levees – build up of sediment along the river bank formed floods when the slower water deposits material
B. Floods
1. Deposit minerals and nutrients on flood plains, making the area fertile for agriculture
2. Flash floods occur on small narrow streams during heavy downpours
3. Floods on large rivers occur due to large amounts of rain of long periods of time
C. Flood Prevention and Control
1. Plant vegetation to control runoff
2. Dams
3. Artificial levees – walls built alongside a stream
4. Spillways – channel built parallel to the main channel in the back swamp to divert water
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