1. Chapter 7- Running Water and Groundwater

2. The Hydrologic Cycle
Hydrologic Cycle: circulation of Earth’s water supply among the oceans, the atmosphere and the continents
Powered by Sun’s energy
Water is transported by:
Evaporation – liquid water converts to gas and rises into atmosphere from land or oceans
Precipitation – gaseous water in atmosphere condenses back into liquid and drops onto land or oceans
Infiltration – water from precipitation soaks into the ground
Runoff – water from precipitation flows over ground surface
Transpiration – water absorbed by plants is released into the atmosphere

3. Runoff, 40
Groundwater Flow
Infiltration

4. Sources of Earth’s water

5. Earth’s Water Balance
Balance in the water cycle means: average annual precipitation over Earth equals the amount of water that evaporates.
Avg Annual Precip=Amt water Evaporated

6. Running Water Importance: Stream: channel of flowing water of any size
Energy
Travel
Irrigation
Fertile floodplains
Shaping of landscape (via erosion)
Stream: channel of flowing water of any size
River – larger streams
Tributaries or brooks – smaller streams

7. Streams flow because of gravity
Streams are supplied by runoff and infiltrating groundwater.
Runoff and groundwater come from precipitation.
Drainage basin: land area that contributes water to a stream.
Divide: imaginary line separating drainage basins.

8. Stream Velocity Stream Velocity: distance water travels in given time
Measured at gauging stations
Stream velocity determines erosional capability
Three factors affect velocity:
Gradient (slope) – expressed as the vertical drop of a stream over a fixed distance. High gradient = high velocity.
Channel characteristics (shape, size and roughness) – more on this in next slide.
Discharge (volume of water flowing per unit time) – High discharge = high velocity. Discharge also affects channel characteristics.

9. Velocity varies within the channel
Highest velocity is in
the center of the channel
Drag slows water along
the bottom, banks, and
top (water-air interface)

11. Stream Channel Characteristics
Channel shape (cross-sectional) affects velocity.
Wide, shallow channel = slower (a lot of friction with streambed).
Semicircular channel = faster (least amount of friction).
Channel size: larger = faster.
Channel roughness: smoother = faster.
Which stream below is faster? A B

12. Running water Upstream-downstream changes Profile
Cross-sectional view of a stream
From head (source) to mouth
Profile is a smooth curve
Gradient decreases from the head to the mouth
Factors that increase downstream
Velocity
Discharge
Channel Size

13. Running water Upstream-downstream changes Profile
Factors that decrease downstream
Gradient, or slope
Channel roughness

14. Longitudinal profile of a stream

15. Running water Base level Lowest point a stream can erode to
Two general types
Ultimate – sea level
Temporary, or local
Changing causes readjustment of the stream – deposition or erosion

16. Adjustment of base level to changing conditions

17. A waterfall is an example of a local base level

18. Geologic Work of Streams – Transportation of Sediment
Running water is the single most important factor in shaping the Earth’s land surface.
By Erosion: Streams erode their channels lifting loose particles by abrasion, grinding, and dissolving soluble materials
By Transportation: Water carries sediments in 3 ways:
In solution (dissolved load) – mostly transported by groundwater
In suspension (suspended load) – most materials carried by streams are suspended loads
Along bottom of channel (bed load) – moves only intermittently

21. Running water The work of streams Transportation
Load is related to a stream's
Competence - maximum particle size
Capacity - maximum load
Capacity is related to discharge

22. Geologic Work of Streams – Deposition of Sediment
Streams deposit suspended sediment when they slow down.
Recall from unit on rocks: fast streams can carry larger particles, while slow streams can only carry smaller particles.
Sorting: particles of similar size are deposited together
Alluvium: material deposited by a stream
Natural levees: an elevated landform that parallels a stream and acts to confine its waters
Alluvial Valleys
Deltas
Alluvial Fans

23. Alluvial Valleys Streams fill part of their valleys with sediment
Changes in hydrologic conditions initiate deposition
Subsequently cut through deposits
Create terraces

24. Deltas Formed by sudden drop in velocity Stream enters ocean or lake
Stream drops sediment load
Evolve by three mechanisms
Growth may be influenced by ocean waves

25. Delta Growth Distributaries Splays Avulsion
Levee and in-stream deposit formation
Channel splits into two smaller channels
Splays
Crevasse allow water to leave main channel
Water spreads out forming a splay deposit
Avulsion
Shift in main course to follow steeper slope

26. Structure of a simple delta

28. Alluvial Fans Accumulation of sediment in a dry basin
Deposition due to rapid velocity drop
Usually arid climate
High sediment load - braided streams
Form fan-shaped deposit

29. Alluvial fans in Death Valley

30. Running water Stream valleys Valley sides are shaped by
Weathering
Overland flow
Mass Wasting
Characteristics of narrow valleys
V-shaped
Downcutting toward base level

31. Running water Stream valleys Characteristics of narrow valleys
Features often include
Rapids
Waterfalls
Characteristics of wide valleys
Stream is near base level
Downward erosion is less dominant
Stream energy is directed from side to side
This eventually produces a floodplain-a flat valley floor
Streams that flow on floodplains move in meanders

32. A narrow V-shaped valley

33. Continued erosion and deposition widens the valley

34. The resulting wide stream valley is characterized by meandering on a well-developed floodplain

35. Erosion and deposition along a meandering stream

36. A meander loop on the Colorado River

37. Braided Streams Multiple channel system
Interlaced channels with islands
High sediment load
Common in arid & semi-arid regions
Seasonal high flows
Common in front of glaciers
Large sediment load, fluctuating water flow

41. Running water Floods and flood control
Floods are the most common geologic hazard
Causes of floods
Weather
Human interference with the stream system

42. Floodplains Floods Floodplains
Normal stage - water level below the bank
Bankfull stage - water level even with the bank
Flood stage - water level above the bank
Floodplains
Areas that will be submerged when a river is at flood stage

43. Running water Floods and flood control Engineering efforts
Artificial levees
Flood-control dams
Channelization
Limiting Development
Nonstructural approach through sound floodplain management

44. Satellite view of the Missouri River flowing into the Mississippi River near St. Louis

45. Same satellite view during flooding in 1993

46. Running water Drainage basins and patterns
Drainage basin: the land area that contributes water to a stream
A divide separates drainage basins of one stream from another
Types of drainage patterns
Dendritic
Radial
Rectangular
Trellis