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 ft 2

Velocity = 1 foot / second

Discharge = 500 ft 2 * 1 ft/sec
 = 500 ft
3 / 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

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 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

Toad River, Canada
River Valleys

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
• Relieve water and sediment overload of the channel
Negative
• Destructive for people near rivers
• Floods deposit minerals on floodplains making these areas fertile for agriculture
• 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


Youthful
 Rapids
 Waterfalls
 Fast-moving water
 Steep slope
Stream Stages

Old
 Broad floodplain
 Meanders
 Oxbow lakes
 Meander Scars

Oxbo w lake depositi on erosio n

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

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