1. Streams
Geology 115

2. Hydrologic cycle

3. Surface water Precipitation falls and becomes overland flow
Overland flow organizes into streams
“Stream” is a generic term covering brooks, creeks, rivers, really any flowing surface water which is not the ocean

4. A stream’s drainage is its watershed
Continental Divide
All of the streams in a drainage are called the stream’s network

5. Stream profile
Base level

6. Stream gradient % gradient = (elevation gain) ÷ s(horizontal distance)
Water velocity is fast
Water velocity is slow
% gradient = (elevation gain) ÷ s(horizontal distance)

7. Streams erode and deposit to fit the ideal profile
The base level may also be affected by rising or falling sea levels

8. Waterfalls alter the stream profile
The underlying rock is quite erosion-resistant

9. As the stream tries to achieve the ideal stream profile, the waterfall retreats as the rock is eroded
Plunge pool develops

10. Niagara Falls State Park, New York

11. The fall line –

12. A stream’s discharge is the volume of water that flows past a given point per time for that stream
When a river floods, its discharge increases, mostly because the stream’s width increases and not so much its depth.

13. Parts of a stream
Tributaries
Headwaters

14. More vocabulary words about streams

15. Braided streams are characteristic of rivers near their headwaters
Denali NP, Alaska

16. Meandering streams are characteristic near their outlet
Vicksburg NMP, Mississippi

17. Floodplain and levee Levee, enhanced with a revetment
Former stream channel
Floodplain

18. Levee, enhanced with a revetment
Floodplain
Cut bank
Point bar

19. Meanders both erode and deposit
Cut bank
Point bar

20. Meanders migrate

21. The material deposited by a stream is called alluvium, which tend to be rich in nutrients, especially metals, which makes for a good soil

22. An alluvial fan is a feature of a stream that emerges from a mountain gorge onto a plain (Death Valley NP, California)

23. Different types of stream mouths - delta
Distributaries
Mississippi River Delta NHA, Louisiana

24. Different types of stream mouths - estuary
Estuaries are major coastal wetlands that provide not only wildlife habitat but also remove metals and organic toxins from streams prior to the ocean
Oregon Dunes NRA, Reedsport, OR

25. Different types of stream mouths – drowned river mouth
Chesapeake Bay

26. Stream evolve over time – for instance, meander migration causes valleys to widen
Oxbow lake

27. Antecedent streams – the stream was there first, and, by gum, it’s going to keep to its path whatever uplift or erosion happens
Fold mountains
Peneplain mountains
Fault block mountains

28. The Potomac River at Harpers Ferry NHP (WV, VA, MD)
These ridges are made of a resistant metamorphic rock called quartzite

29. Consequent streams follow the topography (they don’t cut through)
In this example from Virginia, Beaverdam Creek was an antecedent stream that incised through a ridge of resistant rock; it was captured by Shenandoah River (a consequent stream) in an act of stream piracy.

30. A water gap is where the river cuts through resistant rock (Harpers Ferry NHP)
A wind gap is where the river once cut through resistant rock but has been captured by another river and only a low spot in the hills remains

31. Cumberland Gap NHP (TN, KY, VA) was an important wind gap for Native Americans and settlers through the Appalachian Mountains
Note that fog uses it, too!