# Earth Science- Chapter 13 Mr. Hendricks and Mr. McMahon

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Earth Science- Chapter 13 Mr. Hendricks and Mr. McMahon
Surface Water Earth Science- Chapter 13 Mr. Hendricks and Mr. McMahon

Chapter Outline Streams and River Erosion and Deposition River Valleys
Floodplains and Floods

Streams and Rivers River Systems Vocabulary - Continental Divide:
- Water Shed aka Drainage Basin: - River system - Tributary

River System

River System Definition- A river and all of its tributaries (feeder river or connecting rivers) Example: Mississippi River System

Drainage Basin or Watershed
Drainage Basin or Watershedall is all the land that drains into the river directly or through it’s tributaries. Example: green area is Mississippi R. Basin

Continental Divide Defined as the highland that separates one drainage basin from another. Usually a mountain range Sub-Continental divide in Men. Falls

Tributary A tributary is a feeder river/ creek/ stream that flows into a large parent river. There are some 250 tributaries of the Mississippi which drain a total area of more than 1,247,000 square miles--one third of the nation's landmass!

River Characteristics
Channelized flow- water flows in a chanel Velocity- how fast a river is flowing Gradient- how steep a river is Discharge- how much water is flowing

Velocity How fast something is moving High velocity = high speed
Low velocity = low speed

Channelized Flow Cross section of river displaying channelized flow
Rivers are “Confined” by their channel Affects Velocity of water

Gradient Slope of a stream Rise over Run
A river may drop 10 feet over a distance of 100 feet Gradient is 1/10 or 10%

Discharge Cross Sectional Area = Width * Depth
5 ft * 100 ft = 500 ft2 Velocity = 1 foot / second Discharge = 500 ft2 * 1 ft/sec = 500 ft3 / second

Discharge Volume of water that passes a point over an amount of time
How much water is flowing in a river Cross sectional area * Velocity

Stream Discharge

How to determine discharge
Discharge = Cross sectional area * Velocity Determine the discharge of a stream with the following characteristics: Confined by two vertical walls. The average depth of water is 5 feet. The channel is 100 feet wide Average velocity = 1 foot per second

Discharge Discharge is not constant. Depends on conditions
Increased down river Increased during times of high precipitation or melt Spring = High Discharge

Yearly Discharge

Erosion and Deposition
How does it happen? Mechanical Weathering- Abrasion Running water What does it produce? Sediment Rounded rocks Potholes

Erosion, Transport, and Deposition
Whether sediment is being eroded, transported, or deposited depends on the size of the particle and velocity of water Hjulstrom Curve

Color Hjulstrom

Transportation of Sediment
Load: material transported by river Bedload: moved along bottom, rocks, gravel, pebbles Suspension: clay- silt muddy water Solution: material dissolved in water Capacity: total amount of sediment a stream can carry Competence: Maximize size particles a steram can carry

Deposition Sediment is deposited when the velocity of the current can no longer transport material Examples: A boulder will not be transported by a trickling crick A rapid river will move particles of all sizes because of the high V Silt and Clay is deposited in the deep ocean because there is barely a current (low V)

Color Hjulstrom

Depositional Feautres
Delta Sandbars Deposit Bank

Delta A fan-shaped deposit that forms when a river flows into a quiet or large body of water Where do you think clay particles are deposited on the diagram?

Sand Bars Wisconsin River- How do they form? -Discuss for 2 mins

Sand Bar Formation Current carries sediment
Sediment is deposited when current is slowed down Sediment begins to pile up and catch more sediment Bars constantly move to change in current and water depth

River Deposit

Why do some rivers grow so big?
All rivers start on a small scale Rainstorm forms a valley in loose soils called a gullie Rainstorm ends, water evaporates, but depression remains Next rainstorm, erosion continues As time goes on, a gullie increases length, width, and depth Continuous erosion of land

Headward Erosion The process by which land is worn away at the head of a stream or gully Head: An abrupt drop in elevation Waterfall Erosion opposite the direction of waterflow

Canyons Canyon- river valley with steep vertical sides
Form in areas with low rainfall Factors in formation: Type of rock, amount of water, climate Colorado R. -Grand Canyon)

V-Shaped Valleys Rain erodes the sides of a valley which forms a V shape Deeper channel = greater width Ex: Yellowstone River

Base Level Streams can’t cut any deeper than the body of water they flow into Ultimately, all rivers only can cut to sea level

Rapids and Waterfalls Water flowing over a cliff or steep, jagged slope forms rapids and waterfalls High rate of erosion at Rapids and WF Undermining Temporary features

Undermining 1) Waterfall creates pool 2) Undercuts the waterfall 3) Creates overhang 4) Overhang collapses 5) Recession upstream

Niagara Falls

Dry Niagrara Falls?

Floodsplains and Floods
Features of a Floodplain: Meanders Oxbow Lake Natural Levees

Floodplain Features Meander-River winding back and forth with broad curves

Features Oxbow Lake- A curved body of water that separates a meander from its river Formed due to erosion of river banks

Oxbow Lake

Floodplain Feature Natural Levee- thick deposits alongside stream banks Elevated ridges

Floods Naturally occurring event after heavy or long-lasting rains
Positive and Negative Effects Recent Flooding?

Flood Effects Positive Negative
Relieve water and sediment overload of the channel Floods deposit minerals on floodplains making these areas fertile for agriculture Destructive for people near rivers Cause damage to buildings, farmland, and other properties Dangerous water levels/velocity

Flood Causes For large rivers, like the Mississippi, floods occur after many days of heavy, steady rainfall- No flash floods Spring melt Dam failures- Ex: Lake Delton

Lake Delton

Flood Control and Prevention
People rely on controlling and preventing floods Communities built on flood plains are of special concern Any time a flood occurs their property and their life is at risk

Flood Prevention/Control
Means: Restore natural flood protections Replanting removed vegetation Urbanization = problem Dams Creates reservoir Risk of failure – Lake Delton Eventually fill up with sediment

Flood Prevention Continued
3. Artificial Levees- sandbags Deeper river holds more water May create erosion downstream 4. Spillways Channels parallel to river to collect water

Floodgates

Artificial Levee

Stream Stages Youthful Old ________: _______: Rapids Waterfalls
Fast-moving water Steep slope _______: Broad floodplain Meanders Oxbow lakes Meander Scars

________ – the bends and curves of a stream
Meanders

Oxbo w lake depositi on erosio n

____________ – deposit formed when a stream spreads out onto a less steep area

_____ – where a stream empties into a larger body of water
Delta

____________ – when an old age stream downcuts to “make it new again”
Rejuvenation