1. 6.3 Water Beneath the Surface
Chapter 6
6.1 Running Water
6.2 The Work of Streams
6.3 Water Beneath the Surface

2. The Water Cycle Illustrates the circulation of Earth’s water supply
Processes involved in the cycle
Precipitation
Evaporation
Infiltration
Runoff
Transpiration
>Water cycle drawing worksheet

4. Sources of Earth’s water

5. Running water Streamflow Factors that determine velocity
Gradient, or slope
Channel characteristics
Shape
Size
Roughness
Discharge – volume of water flowing in the stream

6. 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

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

8. Longitudinal profile of a stream

9. Running water Base level Lowest point to which a stream can erode
Two general types
Ultimate – sea level
Temporary, or local

10. Adjustment of base level to changing conditions

11. The Work of Streams Stream channels are eroded through
Abrasion
Grinding
Dissolving soluble materials
Sediment transport
Dissolved load
Suspended load
Bed load

12. The Work of Streams Transportation of sediment
Load is related to a stream’s
Competence – maximum particle size a stream can transport
Capacity – maximum load
Capacity is related to discharge… The greater the volume of water in a stream, the greater its capacity for carrying sediment

13. The Work of Streams Deposition Caused by a decrease in velocity
Competence is reduced
Sediment begins to drop out
Stream sediments
Known as alluvium, or well-sorted deposits from a stream

14. The Work of Streams Deposition Features produced by deposition
Deltas – exist in ocean or lakes
Natural levees – Form parallel to the stream channel

15. Formation of natural levees by repeated flooding

16. The Work of Streams Stream valleys Characteristics of narrow valleys
V-shaped
Downcutting toward base level
Features often include
Rapids
Waterfalls

17. A narrow, V-shaped valley

18. The Work of Streams Stream valleys Characteristics of wide valleys
Stream is near base level
Downward erosion is less dominant
Stream energy is directed from side to side
Floodplains
Features often include
Meanders
Cutoffs
Oxbow lakes

19. Continued erosion and deposition widens the valley

20. A wide stream valley is characterized by meandering on a well-developed floodplain

21. Formation of a cutoff and oxbow lake

22. Erosion and deposition along a meandering stream

23. A meander loop on the Colorado River

24. The Work of Streams Floods and flood control
Floods are the most common geologic hazard
Causes of floods
Weather
Rapid spring snow melt
Storms / heavy rains
Human interference with the stream system
Dam or levee failure
Building / developing on wetlands

25. The Work of Streams Floods and flood control Engineering efforts
Artificial levees
Flood-control dams
Minimizing development on floodplains, allowing floodplains to naturally absorb floodwaters

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

27. Same satellite view during flooding in 1993

28. The Work of Streams Drainage basin
Land area that contributes water to a stream
A divide separates drainage basins

29. Drainage basins and drainage divides

30. Water beneath the surface (groundwater)
Largest freshwater reservoir for humans
Geological roles
As an erosional agent, dissolving by groundwater produces
Sinkholes
Caverns
Helps to maintain a steady streamflow

31. Water beneath the surface (groundwater)
Distribution and movement of groundwater
Distribution of groundwater
Belt of soil moisture (close to the surface)
Zone of saturation
Zone of Aeration (unsaturated zone)
Pore spaces in the material are filled mainly with air

32. Water beneath the surface (groundwater)
Distribution of groundwater
Zone of saturation
All pore spaces in the material are filled with water
Water within the pores is groundwater
Water table – the upper limit of the zone of saturation

33. Features associated with subsurface water

34. Water beneath the surface (groundwater)
Distribution and movement of groundwater
Movement
Porosity
Percentage of pore spaces
Ability to store water
Permeability
Ability to transmit water through connected pore spaces (water can flow through)
Aquitard – an impermeable layer of material
Aquifer – a permeable layer of material

35. Water beneath the surface (groundwater)
Springs
Hot springs
Water is 6–9°C warmer than the mean air temperature of the locality
Heated by cooling of igneous rock
Geysers
Intermittent hot springs
Water turns to steam and erupts

36. Old Faithful geyser in Yellowstone National Park

37. Water beneath the surface (groundwater)
Wells
Pumping can cause a drawdown (lowering) of the water table
Pumping can form a cone of depression in the water table
Artesian wells
Water in the well rises higher than the initial groundwater level

38. Formation of a cone of depression in the water table

39. Artesian systems

40. Water beneath the surface (groundwater)
Environmental probs with groundwater
Treating it as a nonrenewable resource
Removing it faster that it can be replenished
Land subsidence caused by its withdrawal
San Joaquin Valley, California
Contamination
Septic, Farm waste, inadequate or broken sewers

41. Water beneath the surface (groundwater)
Geologic work of groundwater
Groundwater is often mildly acidic
Dissolves calcite in limestone
Caverns
Formed by dissolving rock beneath Earth’s surface
Formed in the zone of saturation

42. Water beneath the surface (groundwater)
Geologic work of groundwater
Caverns
Features found within caverns
Form in the zone of aeration
Composed of dripstone / Travertine
Calcite deposited as dripping water evaporates
Common features include stalactites (hanging from the ceiling) and stalagmites (growing upward from the floor)

43. Cave Features in Lehman Caves, Great Basin National Park, and Carlsbad Caverns National Park

44. Water beneath the surface (groundwater)
Geologic work of groundwater
Karst topography
Formed by dissolving rock at, or near, Earth’s surface
Common features
Sinkholes – surface depressions
Sinkholes form by dissolving bedrock and cavern collapse
Caves and caverns
Area lacks good surface drainage (few streams if any, water is mostly funneled underground)

45. Features of karst topography