Surface Water
Primary erosional force on earth
Possible outcomes for surface water
Evaporation
Infiltration
Run off
Streams
Any water flowing on the surface of the earth
Characteristics of streams depend on many things
Water volume and velocity
Slope
Sediment
Many “types” of streams evolve into other types as these parameters change
General Stream types
Mountain streams
Braided streams
Meandering streams
Flood plains
Know the features for each and how they are different
Mountain (Youthful)
rocky and steep (white water and high velocity)
generally small
Braided stream
foothills of mountains
very wide with many channels
shallow with lots of rocks
Meandering streams (maturing)
broad valley with few rocks
streams creates “s” pattern
low slope and large volume of water
Floodplain (Most mature)
very broad valley and low slope
large meanders & largest volume of H2O
mostly clay, mud and sand
Longitudinal profile
Change of a streams features from the headwaters to the coast.
How do streams change as they move away from their headwaters?
Factors affecting Stream’s Characteristics
Velocity
affected by gradient
channel shape (width to depth ratio)
which would have a higher velocity flow and why: shallow stream or deep stream
(equal volumes of H2O)
where is max velocity in a stream?
Thalwag
channel roughness
volume
Discharge
Volume of water flowing past a point at a given time
m3/second Width x Depth x Velocity
A stream is 3m wide and 6m deep. It is flowing at 3m/s. What is the discharge of the
stream?
Turbulent vs. Laminar flow
Capacity vs. Competence
Stream capacity:
maximum load of solid particles a stream can carry
Reported as a volume (m3)
Stream competence:
maximum size of particles a stream can carry
Reported as a size (mm or cm)
Question: which stream would have the highest capacity and competence-->
large stream immediately after a long heavy rain or a large stream in the middle of the
summer?
List three ways/methods that streams transport material?
Stream Loads
Dissolved load--> carried in solution (can’t see)
ions from chemical weathering
won’t settle out in still water
won’t affect the behavior of the stream
expressed as parts per million (ppm)
Suspended load
small visible particles such as clay and silt
settles out in still water
increases during peak discharge
Bed load
sand, gravel boulders
moves by saltation and traction
intermittent motion
causes erosion of stream bed
The amount of dissolved, suspended or bed load is unique to each river
Dependent on location and type of rock in area
Can change depending on discharge
Compare and contrast the load found in the Columbia river and the Mississippi river
Tributaries, Drainage Basins, and Divides
Tributaries
Streams that feed into larger streams
Drainage basin
Region that feeds a river system
Divide
Topographic high which determines which direction precipitation will drain/flow
Why do streams erode their channels downward?
Streams erode their channels downward creating a “V” shaped valley
Base Level
What is the base level of a stream?
What is ultimate base level?
What is meant by a temporary base level?
What are some things that can form temporary base levels?
Can base levels change?
Streams erode their channel to base level
When a stream stops eroding downward it is called a “Graded Stream”
Graded streams remove material that erode into their channels but don’t cut
downward.
Streams rarely stay in a graded state for long
Changing a base level of a stream changes the characteristics of a stream
alters velocity-->changes load capacity--> changes erosion capabilities
What happens when a dam is installed on a stream
What are some of the features created by the change in base level
Features Created by Change
Terraces
Incised meanders
Rejuvenated topography
Deposits and features of a meandering stream
where does deposition occur
point bars
where does erosion occur
cut banks
where is velocity the highest and the lowest?
Cut off meanders and oxbow lakes
levees
back swamps
Yazoo tributaries
Other river features
Headward erosion
Stream Piracy
Deltas
Created when a stream enters standing water (ocean or lake)
distributaries (bird foot structure)
Mississippi delta over time
Flooding
How can flooding be mitigated?
Should it be mitigated?
Recurrence intervals
Flood Control
Levees and river channels
Mississippi Riverà more in a minute
Dams
Is Flood control good or bad?
Mississippi River and Flood Control
River system has been surrounded by levies to prevent flooding The main stem levee
system, is 2,203 miles long
What has been the effect of this on this area?
Sediment distribution?
Atchafalaya river
Old River Control Structure
Why is it so important to preserve the Mississippi river’s current channel?
New Orleans
Levee system for river and hurricanes:
Primary reason for flood was breaking of levees from lake Pontchartrain
Reason for levees in the first place?
