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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 chanelVelocity- how fast a river is flowingGradient- how steep a river isDischarge- how much water is flowing
Velocity
How fast something is movingHigh velocity = high speedLow velocity = low speed
Channelized Flow
Cross section of river displaying channelized flowRivers are “Confined” by their channelAffects Velocity of water
Gradient
Slope of a streamRise over RunA river may drop 10 feet over a distance of 100 feetGradient is 1/10 or 10%
Discharge
Cross Sectional Area = Width * Depth5 ft * 100 ft = 500 ft2
Velocity = 1 foot / secondDischarge = 500 ft2 * 1 ft/sec= 500 ft3 / second
Discharge
Volume of water that passes a point over an amount of timeHow much water is flowing in a riverCross sectional area * Velocity
Stream Discharge
How to determine discharge
Discharge = Cross sectional area * VelocityDetermine 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 wideAverage velocity = 1 foot per second
Discharge
Discharge is not constant. Depends on conditionsIncreased down riverIncreased during times of high precipitation or meltSpring = 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 riverBedload: moved along bottom, rocks, gravel, pebblesSuspension: clay- silt muddy waterSolution: material dissolved in waterCapacity:
total amount of sediment a stream can carryCompetence:
Maximize size particles a steram can carry
Stream Load
Stream Load
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 crickA rapid river will move particles of all sizes because of the high VSilt and Clay is deposited in the deep ocean because there is barely a current (low V)
Color Hjulstrom
Depositional Feautres
DeltaSandbarsDeposit Bank
Delta
A fan-shaped deposit that forms when a river flows into a quiet or large body of waterWhere 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 sedimentSediment is deposited when current is slowed downSediment begins to pile up and catch more sedimentBars constantly move to change in current and water depth
River Deposit
River Valleys
Toad River, Canada
Why do some rivers grow so big?
All rivers start on a small scaleRainstorm forms a valley in loose soils called a gullieRainstorm ends, water evaporates, but depression remainsNext rainstorm, erosion continuesAs time goes on, a gullie increases length, width, and depthContinuous erosion of land
Headward Erosion
The process by which land is worn away at the head of a stream or gullyHead: An abrupt drop in elevationWaterfallErosion 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• Relieve water and
sediment overload of the channel
• Floods deposit minerals on floodplains making these areas fertile for agriculture
Negative• 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:
1. Restore natural flood protections
– Replanting removed vegetation
– Urbanization = problem
2. 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
________:RapidsWaterfallsFast-moving waterSteep slope
_______:Broad floodplainMeandersOxbow lakesMeander Scars
Youthful Old
________ – the bends and curves of a stream
Meanders
Oxbow lake
deposition
erosion
____________ – 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