Hydrology, Running Water,
Erosion, and Sediment Transport

Pamela J. W. Gore
Georgia Perimeter College

Objectives

  1. Describe the basics of the hydrologic cycle.
  2. Discuss erosion and the transport of sediment by streams. Include types of load (bed load, suspended load, dissolved load), stream capacity, and stream competence).
  3. Describe the process of stream erosion and list the various erosional features.
  4. Discuss the processes of stream flow (turbulence, laminar).
  5. Discuss drainage basins and patterns of streams (dendritic, radial, trellis, rectangular).
  6. Discuss the stages of stream erosion (Youthful, Mature, Old Age, and Rejuvenated)
  7. Discuss stream deposition and depositional features. Include meandering and braided streams.
  8. Discuss the concepts of base level, discharge, and gradient.

Outline

Notes:

Hydrologic cycle

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Distribution of water on the Earth

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Where does our water supply come from in Atlanta?

Chatahoochee River (mostly)

Investigation: Where does your water come from? How is it treated before it gets to you? What chemicals are in it?

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Running Water, Erosion, and Sediment Transport

Q. Why does water flow downhill?

Ozone Falls, Tennessee

A. Gravity

Types of stream flow

  1. Laminar (straight line paths) - low velocity
  2. Turbulent (multidirectional movement) - hi velocity

Discharge

Discharge = amount of water flowing past a point in a given unit of time

Class to think about this.

Urbanization and its effects on discharge

Specific causes:

What does runoff do?

Types of erosion

Hjulstrom diagram

(See instructor for copy of diagram)

Settling velocity

Jar of sediment and water

Clay takes the longest to settle (see Hjulstrom diagram)

Transport of Sediment by Streams and Rivers

The material transported by a stream can travel as:

  1. Bed load
  2. Suspended load
  3. Dissolved load (salts, chemicals)

Stream capacity

Directly related to discharge

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Stream competence (or competency)

Types of rivers or streams

  1. Meandering

    These streams are very sinuous, and tend to migrate back and forth across the floodplain (or meander), over time. The word "meander" comes from the name of a sinuous river in Turkey, named the Menderes.


    Meanders on the Tennessee River, Chattanooga, TN.


    Know the parts of a meandering stream

  2. Braided

    These streams have lots of lenticular-shaped in-channel bars. The stream channel bifurcates around these bars, and follows a pattern resembling braided hair.

Parts of a stream

Terms to know:

Photos of Rivers

Note that levees are built up to prevent flooding, but may actually lead to more severe flooding.

Scenario:

  1. River channel fills with silt over time
  2. River bottom and water level rise over time (silt displaces water)
  3. Levees and dikes constructed to confine river
  4. Flood waters top or burst through confinements, or go around upstream end

In the photos below, note that the level of water in the river is higer than the level of the surrounding land (floodplain) on the other side of the levee.


Levee in New Orleans. Note the water level in the channel is well above the level of the surrounding land.


Atop the Mississippi River Delta in New Orleans. Note the river level is approximately the same as the bottom of the rooftops visible at left.


Floodwall and flood gate on the top of the Mississippi River levee in New Orleans, beside the Jackson Brewery. When river levels rise, the brown metal gate (center), rolls to the right to block flood waters. Note the railroad tracks also on the levee.

Floods

Floods = any high flow of surface waters that overtops normal confinements or covers land normally dry

Types of floods

Floods are the most devastating of all geologic agents - exceeded only by plagues, world wars and the Holocaust in loss of life.

Sites of worst floods - China's rivers

Larger figures include deaths from flood-induced famine, water-born diseases (cholera)

Recent major floods

Flood mitigation

  1. Flood control structures
    1. dams
    2. flood walls
    3. channelization
    4. dikes
    5. levees
  2. zoning
  3. prohibition of rebuilding; moving towns
  4. flood insurance
Controversies

Flood insurance

This information is from the Atlanta Journal-Constitution, March 29, 1998.

Homeowners insurance policies do not provide coverage for flood damage (except for mobile homes). To protect your home against floods, you have to buy a flood insurance policy from the National Flood Insurance Program. To be able to buy the flood insurance, you must live in a community that has joined the National Flood Insurance Program, which is administered through FEMA (Federal Emergency Management Agency). To qualify for coverage, communities are required to adopt zoning and other guidelines to reduce the danger of flooding. Your insurance agent's company probably writes flood policies under the government program. You can insure your home for up to $250,000 for the building and an extra amount (up to $100,000) for contents. Rates vary, but you have to pay about $300 a year for $100,000 of coverage. For homes in low to moderate risk areas, there is a policy that costs somewhat less (about $100 per year). Coverage under flood insurance does not begin until 30 days after you purchase it, so don't wait until the creek starts to rise to call your insurance agent. For other information about flood insurance, call the National Flood Insurance Program at 1-800-638-6620, or check the FEMA site on the web .

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This page created by Pamela J. W. Gore
Georgia Perimeter College,
Clarkston, GA

October 25, 1995
Modified April 3, 1998
Modified November 6, 1998
Modified July 17, 1999
Modified Sept 1, 2005