Hydrology, Running Water,
Erosion, and Sediment Transport
Pamela J. W. Gore
Georgia Perimeter College
- Describe the basics of the hydrologic cycle.
- Discuss erosion and the transport of sediment by streams. Include types of load (bed load, suspended load, dissolved load), stream capacity, and stream competence).
- Describe the process of stream erosion and list the various erosional features.
- Discuss the processes of stream flow (turbulence, laminar).
- Discuss drainage basins and patterns of streams (dendritic, radial, trellis, rectangular).
- Discuss the stages of stream erosion (Youthful, Mature, Old Age, and Rejuvenated)
- Discuss stream deposition and depositional features. Include meandering and braided streams.
- Discuss the concepts of base level, discharge, and gradient.
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- Powered by and gravity
- Evaporation and precipitation
- Continuous recycling of water
- Where does water go that falls on the land?
- Temporary storage as snow and ice
- Temp. storage in lakes
- Temp storage in plants (evapotranspiration) and animals
- Chem reactions with rocks and minerals
- Source of additional water? volcanism (steam)
- Volcanism also causes melting of snow caps and mudflows as meltwater
mixes with ash
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- Total = 326 million cubic miles
- 97.2% oceans
- 2.15% ice caps and glaciers
- .65% lakes, streams, groundwater, atmosphere
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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Q. Why does water flow downhill?
Ozone Falls, Tennessee
Types of stream flow
- Laminar (straight line paths) - low velocity
- Turbulent (multidirectional movement) - hi velocity
- Picks up sediment (erosion) and keeps it in suspension
Discharge = amount of water flowing past a point in a given unit of time
- Units of measure
Class to think about this.
- How is discharge determined?
- x-sectional area of stream x velocity
- How to measure?
- Why would you be interested in measuring discharge?
- enough water for a business or industry?
- Predict flood extent downstream using data on flood waters upstream from
- Test question - How could you measure discharge ? What could discharge measurements be used for?
(What are some practical applications in personal life, business world, or government?)(
- Less infiltration
- More runoff
- More flooding
- Construction and paving
What does runoff do?
Types of erosion
- Abrasion (potholes)
Potholes, Great Smoky Mountains National Park, Tennessee
- Scour (lifting loose particles)
Great Falls, Maryland
(See instructor for copy of diagram)
- Velocity vs. grain size
- Note major sediment sizes
- Increase of velocity needed to lift heavier/larger grains
- What about clay?
- unusual - cohesive, flat, hard to pick up
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:
- Bed load
- Suspended load
- Dissolved load (salts, chemicals)
Directly related to discharge
- Maximum quantity of solid material that a stream can carry
- Related to velocity (discharge)
- Higher after a rain (more sediment in water)
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- Measure of the maximum size of particles the stream can transport
- Predict erosive capabilities
Types of rivers or streams
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
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:
- Channel (note location of maximum velocity - in deeper part of stream near outer part of curve in meandering systems)
- Floodplain - tends to be covered by silt and mud deposited by lower-velocity floodwaters
(nutrient-rich deposits producing fertile lands for agriculture) - example Nile River valley.
- Point bars - form on inside of curves of meandering streams or rivers
(white deposits seen on stream banks in bottom of photo above)
- In-channel bars - form in braided streams
- Levees (natural and man-made)
- Cut-bank - forms on outside of curve of meandering streams or rivers due to higher water velocity,
which causes erosion on outside of curves (see photo above).
- Oxbow lakes (form through neck cut-offs in meandering systems)
- Meander scars
- Incised meanders may occur in a situation where the land was uplifted, or where base level (sea level) dropped,
such as during the Ice Ages.
Photos of Rivers
Note that levees are built up to prevent flooding, but may actually lead to more severe flooding.
- River channel fills with silt over time
- River bottom and water level rise over time (silt displaces water)
- Levees and dikes constructed to confine river
- 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 = any high flow of surface waters that overtops normal confinements or covers
land normally dry
Types of floods
- Riverine floods (hurricanes)
- Flash floods (cloudbursts, short)
- Floods caused by human interference (see urbanization above)
- Dams burst
- Deadliest flood in US history was due to dam breaking: Little Conemaugh River,
Johnstown, PA, May 31, 1889, wall of water 40 feet high, 2200-3000 killed
- A second dam failure there in July 1977, 77 killed
- Nov 6, 1977, a dam broke upstream of Toccoa Falls College in Georgia, killing 39
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)
- 1887 Yellow R. 900,000 - 6 million lives lost
- 1911 Yangtze R. 100,000
- 1931 Yangtze R. 3,700,000
- 1939 Yellow R. 200,000
Recent major floods
- August/September 2005 New Orleans, Hurricane Katrina
- 1993 Mississippi and Missouri Rivers
Mississippi River flooding
- July 1994 Georgia, Flint and Ocmulgee Rivers
- 1996 Oregon and Washington
- 1997 Ohio and Mississippi Rivers
- April 1997 Red River, North Dakota, South Dakota, and Minnesota
- October 1998 Texas and Kansas
- Flood control structures
- flood walls
- prohibition of rebuilding; moving towns
- flood insurance
- channelization - drains wetlands
- damming - causes siltation, erosion downstream
- some municipalities voting to remove floodwalls because they are unsightly and
spoil the view of the river
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,
October 25, 1995
Modified April 3, 1998
Modified November 6, 1998
Modified July 17, 1999
Modified Sept 1, 2005