Rivers and Streams

• Rivers and Streams

  Why do we care?

  -Major agent of weathering and erosion

  -Major source of water

  -Can be damaging when they flood
• drainage basin


  entire area around a river where the water flows into that area

  -the area from which a single stream or river and its tributaries drains all of the water
• Channels


  area where the water is actively flowing in a river

  -V-shaped valley (relatively straight sides)
• Tributaries


  small rivers and streams that feed water into the bigger one
• #1 Branching/dendritic


  most common
• #2 Radial


  -Area in the center has the highest elevation

  -Helps spot highest point
• #3 Rectangular


  Indicates you have a lot of faults or joints in the area (cracks)
• Levee: low ridge up against the river


  Floodplain: area that is going to flood if the water comes over the levee
• Channels

  Braided Streams


  multiple chanells about the same size twisted together

  Causes

  -variable water

  discharge

  -Large sediment supply

  -easily erodable banks
• Steep elevation gradients


  Causes water to flow fast and straight if the elevation is steep
• In areas of lower gradient, channels start meandering


  meandering: big loops from side to side
• Cut Bank: outer part of the bank, allows the water to flow fast, erodes the side


  Point Bar: inside of the pant, allows the water to slow fast and sediment is deposited and can form sand bars
• Meanders migrate over time


  Erodes the cut back side of the channel causing it to migrate
• Oxbow lakes (aka oxbows)


  land is eroded away causing the lake to form into a horseshoe shape standing on their own
• Meander vs Man


  - meandering causes problems for people

  - can artificially straighten but also causes problems (tend to flood more easily and frequently)

  ex: MI river in New Orleans has been artificially kept in place
• How much water moves past a point in a given amount of time?

  Discharge = velocity x area

  -If Discharge increases until channel cannot contain all the water, flooding occurs
• Recurrence interval


  what is the probability occurrence a river will flood

  -Probability in a given year = 1 / interval
• Caveats


  •Probability, not guarantee

  •Varies from river to river
• The End of the River


  -Mouth- where the river empties out into a ocean, sea, etc.

  -Erosion ends, deposition commences

  -Distributaries- where the main channel breaks into branches that distributes the water over a wider area

  -Deltas- area around the mouth and distributaries that create a triangle; swampy and marshy
• Delta Processes:

  Subsidence


  sinking or lowering of ground level

  -Because of the depositing of so much sediments by rivers

  --EX: Venice Italy, can ride boats through cities but now areas are being flooded due to subsidence
• Water Quality- Clean-Up


  Clean-up possible but difficult

  -takes time & money

  
  

  Faster recharge = easier to clean once contaminant source is isolated

  -'Fast' recovery = matter of years
• Water Availability


  -Legal fights among states over who gets how much water from a reservoir

  -'Downriver' states suing 'upriver' states for taking too much

  -Upriver states say old water use agreements are outdated
• Case Study- SC vs NC


  -10 million gallons from the Catawba River annually

  -Catawaba R accounts for about half the water supply to the SC low country

  =Taken before US Supreme Court
• Case Study- Savannah River


  -SC & GA are in contention over the Savannah River
• Case Study- GA vs TN


  -GA state legislature has proposed legislation to move the state border about 1mile north

  -Claim is based on an 1818 surveying error placing the border at the wrong location
• Case Study- Everyone in the SW US vs Everyone Else in the SW


  Colorado River lawsuits date back to 1931

  -CA, AZ, NV, NM, UT, & Native American groups
• Colorado River Overuse


  -Providing water to 30 million people

  -70% of its water diverted to irrigate 3.5 million acres

  -10 years of drought

  -Water level down 130 ft since 2000 in some areas

  -Flow est. to drop 5-20% in next 40 yrs due to climate change

  -Ends 50 miles before even reaching the Pacific Ocean

  -Delta reduced from 3,000 acres to 250 acres in < 100 years
• Future Case- Water Wars?


  What happens in areas where courts aren't available to settle disputes?

  -2010: 1 billion people in water stressed regions (16% of pop-)

  -2050: Est to be 2 billion (22% of pop-)