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. Water on Earth is ~Constant
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
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