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Streams
- A. GENERAL TERM FOR RIVERS, CREEKS,ETC
- B.STREAMS ARE VERY IMPORTANT EROSIONAL AGENTS
- C. STREAMS ERODE, TRANSPORT, AND DEPOSIT MATERIAL
- D. STREAMS DO MOST OF THEIR WORK DURING FLOODING
- E. LONGITUDINAL PROFILE OF A STREAM
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STREAM CHARACTERISITCS
- A.VELOCITY
- 1.Distance water travels in given unit of time
- 2. Velocity determines how much a material a stream can erode and transport
- 3. Velocity is influenced by
- a. Gradient
- i. Slope of stream channel
- ii. Vertical drop over horizontal distance ft/mi, m /km
- b.Discharge
- i. Volume of water flowing past certain point-ft3/sec, m3/sec
- c. Size and shape of the channel and size of material in channel
- i. Large boulders impede the velocity of the stream
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Work Streams
- A.EROSION
- 1. Lifting and removal material
- 2.. Hydraulic action
- a. Force of running water loosens and lifts material
- 3. Abrasion- material transported along channel has an abrasive effect
- B. TRANSPORTATION
- 1. Dissolved load
- a. Ions transported in solution
- b. Derived primarily from chemical weathering
- 2. Suspended load
- a. Sediment transported in the water column
- b. Usually clay, silt and fine sand
- 3. Bedload
- a. Material transported along channel bottm
- b. Sand and larger sized sediment
- C. DEPOSITION
- 1.Alluvium
- a. Sediment deposited by streams
- b. Critcical settling velocity
- i. Largest particles settle first
- ii. Clay sized particles wont settle until there is little turbelence to keep sediment suspended
- 2. Deltas
- a. Depostional features formed when strams enter lake or ocean
- b. Have an overall triangular shape
- c. Delta Deposits
- i. Topset beds
- ii. Forest beds
- iii. Bottomset beds
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Base Level
- A. LOWEST LEVEL TO WHICH A STREAM CAN ERODE ITS CHANNEL
- B. ULTIMATE BASE LEVEL
- 1. Sea level
- a. Streams cannot erode their channels below sea level bc they need gradient to flow
- C.TEMPORARY BASE LEVEL
- 1. May formed by lakes or resistant layers of rock along course of stream
- 2. Limits the amount of downcutting may occur upstream from a dam or resistant rock layer
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STREAM VALLEYS
- A. NARROW STREAM VALLEYS (youthful stage)
- 1. Form where streams are high above base level
- 2. Characteristics
- a. V-shaped valley
- b. Downcuttin is dominant
- i. Stream is cuttin its valley deeper
- c.Rapids and waterfalls
- d. Lacks a floodplain
- B. WIDE STREAM VALLEYS (mature to old stage)
- 1. Form where streams are close to base level
- 2. Features of meandering streams
- a. Wide stream valley
- b. Dominant work is lateral erosion
- c. Floodplain-flat valley floor between valley walls
- d. Meanders-looping bends in streams
- e. Points bars-deposits of sand on the inside of the meander (slowest velocity)
- f. Cut banks-highest velocity is on the outside of the meander-erosion occurs
- g. Oxbow lakes- form when a river cuts off a meander
- h. Natural Levee
- i. Deposit of fine sand along stream change
- ii. Form during successive floods
- i. Braided Streams
- i. Bedload streams
- ii. Network of channels
- C. REJUVENATION
- 1. Stream terraces- Older, higher, abandoned floodplain
- 2. Entrenched stream meanders- streams that meander but have no floodplain
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DRAINAGE BASINS AND DIVIDES
- A. DRAINAGE BASIN- Arrea that contributes water to a stream
- B DIVIDE-SEPEATES DRAINAGE BASINS
- C. TYPES OF DRAINAGE PATTERNS IN DRAINAGE BASINS
- 1. Dendritic pattern
- a. Tributaries join in a treelike branching pattern
- b. Forms in areas underlain by fairly unifrom rock types
- 2. Rectangular pattern
- a. Streams join at right angles
- b. Pattern is controlled by joints in the underlying bedrock
- 3. Radical pattern
- a. Streams diverge in all direction from high area such as volcano
- b. Pattern controlled by topography
- 4. Trellis pattern
- a. Tributary streams are parralel
- b. Forms where the underlying beds are folded
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Floods and Flood Control
- A. FLOODING IS CAUSED BY WEATHER-low pressure systems or heavy spring snow melts
- B. STRUCTURES CREATED TO CONTROL FLOODING
- 1.Artificial levees
- a. Built on top of natural levees or where no levees exist
- b. Keeps water channelized
- c. Increases flooding downstream
- 2.Flood-control dams
- a. Built to trap floodwaters and slowly release them
- b. After streams in various ways
- 1. Effect ecology of streams
- 2. Reservoirs cover large areas of unsable land
- 3. Artificial cutoffs
- a. Meanders are cutoff by humans
- b. Increases gradient of stream
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