Surface Water 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 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