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Water, Water Everywhere

Water, Water Everywhere. “Splish, Splash, I was Takin’ a Bath…”. 1.3 billion cubic km of water at Earth’s surface Oceans and seas Account for ~96% Of water on Earth Fresh water only Accounts for ~4%. Recap: The Four Spheres. Geosphere, atmosphere, hydrosphere, biosphere.

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Water, Water Everywhere

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  1. Water, Water Everywhere

  2. “Splish, Splash, I was Takin’ a Bath…” • 1.3 billion cubic km of water at Earth’s surface • Oceans and seas Account for ~96% Of water on Earth • Fresh water only Accounts for ~4%

  3. Recap: The Four Spheres • Geosphere, atmosphere, hydrosphere, biosphere

  4. The Hydrologic Cycle Water on Earth is ~Constant

  5. Following the Path… • Water that falls on land follows one of 4 paths • Runoff—streams and rivers • Ground water—water that has seeped into the ground • Transpiration—water created by plants • Incorporated into animal and plant tissue

  6. Streams

  7. What is a stream? • Water flowing in a channel, regardless of size • River: • A large stream fed by smaller tributaries • Ex: the Nile

  8. How do streams form? • Sheet flow: • Overland flow of water—usually as a thin “film” • Irregularities in surface cause local concentrations of flow--rills • Abrasion and positive feedback • Preferential path for water to flow, abrasion increased • Water can also dissolve rock

  9. Stream Velocity • Factors affecting velocity • Gradient—steepness of slope—steep slope = higher velocity • Discharge—amount of water flowing down a stream—velocity increases as discharge increases • Channel Characteristics—shape of bed (floor) and banks (sides)—friction between moving water and bed/banks—higher velocity in center of stream

  10. Discharge in more detail… • Width and depth of a stream multiplied by the speed of the water • The volume of water that passes by a point in a given amount of time

  11. Flow and Lift • As flow gets faster and deeper: • Can move particles from pebbles to boulders depending on speed of the flow • Occurs because movement of water over particles acts to lift them (like a plane wing) • Floodplains = very slow water, deposition

  12. Competence vs. capacity • Capacity: • Total sediment load carried by a flow • Increases with volume • Competence: • A flow’s ability to carry material of a given size • Increases with velocity Incompetence

  13. Suspended Load • Particles temporarily or permanently suspended in flow • Size and amount increases with velocity

  14. How can particles be suspended? • Gravity acts against the lift of turbulence • Settling velocity • Depends on weight and shape • Most particles are suspended for only a short time • Saltation

  15. Bed Load • Particles carried along stream by rolling or sliding • Bed load greater particle size than suspended • Size and amount increases with velocity

  16. Dissolved Load • Ions dissolved in water • Dependant on discharge and chemistry • In some rivers50% of sediment load—smaller for streams • Salty oceans

  17. So… What Does All of This Mean? • The faster the current, the larger the particles carried as suspended load and bed load • High velocity streams have the potential to carry more and larger stuff!

  18. Stream Development • Downcutting • Walls collapse and river widens • Limited by base level

  19. Highland Streams (aka: youthful) • In mountains, stream valleys are narrow, steep and there is little or no floodplain • V-shaped valley • High energy, downcutting prominent

  20. Lowland Streams(aka: old streams) • In lowlands, stream valleys are wide, gentle, and the floodplain is very wide • Low energy, mass wasting, deposition

  21. Stream Development

  22. Low-gradient (old) Stream Features • Low-sediment load, low velocity • Nearly flat floodplains • Meander loops • Cut banks and point bars • Oxbow lakes

  23. Braided Streams • Occur when more sediment is supplied to a stream than it can carry • Main stream channel is filled, water spills out—new channels eroded • Common in deserts and near glaciers

  24. Drainage Basins • Major rivers fed by smaller tributaries • Mtn ranges separate adjacent river systems • Drainage Basin • The region drained by a single river

  25. Floods • More water than stream can hold • Spills over side of stream onto flat flood plain • Not always destructive • Ecosystem value • Sediment—delta • Fertile soil and flat ground

  26. Floodplains + levees • Water spills out during floods • Form natural levees • Can hold back water even at higher levels • The danger of artificial levees

  27. Mississippi River • Flood control • Levee system—prevents flood sediment from accumulating • Increases water velocity • If breached, more severe flooding • False sense of security • Hurricane Katrina and New Orleans • High water + levee breach = city wide flooding • N.O. elevation at or below sea level

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