Stream Dynamics

1. 1 Stream Dynamics Weathering Erosion Processes which impact the course of a river over time. Deposition Stream discharge Gradient (slope) Tectonics

2. 2 Factors which influence water velocity Stream Discharge The volume of water in a stream. As discharge increases, velocity increases. As velocity increases, kinetic energy ______________ increases As kinetic energy increases, the size and amount of weathered material the stream can transport _____________ increases As water velocity increases, erosion ___________ increases During what time of the year will the greatest stream erosion occur in New York ? Spring Why ?

3. 3 Downcutting and Lateral Erosion: When water velocity is high and the force of erosion is directed downwards, downcutting deepens the stream channel. When downcutting is dominant, streams will have: A straight channel A rocky stream bed Rapids and waterfalls

4. 4 Downcutting is dominant in this stream in Ithaca , NY.

5. 5 With gradual slopes and softer bedrock or sediment, lateral erosion dominates. With erosion directed toward the banks of the stream, the channel begins to change. Ox-Bow Lakes Over time, the bends become more eccentric. Eventually, the bends may get cut off forming Ox-Bow Lakes.

6. 6 Stream Features Channel: The path the stream follows. Meanders : The bends in the river channel. Cut bank: The outside of a meander where erosion occurs. Point Bar: The inside of the bend where deposition takes place.

7. 7 Water always seeks the path of least resistance as it flows toward the lowest points. A straight channel is most likely found where slopes are steep and the stream bed is resistant rock. With changes in slope and bedrock resistance, the channel begins to change. Erosion at the outside of the channel Inside: slower flow Depositionat the inside of the channel Outside: Faster flow This process forms meanders.

8. 8 Stream Bed Profiles X Y Point Bar Cut bank A B Cut bank Point bar

9. When the channel is straight, the stream bed becomes symmetrical. 9 Fastest flow is always: Above the deepest part Just below the surface S T

10. 10 Deposition at the mouth of a river. Formation of a Delta. As the river enters a body of water, velocity decreases. Due to the loss of Kinetic energy, transported material is deposited. ( Drops out ) Particle size decreases Horizontal sorting results from the gradual slowing of the river. The Delta grows as sediments are deposited.

11. 11 This sequence of sedimentary rocks indicates a delta deposit. Deltaic deposition coarse Conglomerate Sandstone Siltstone Shale The Catskill region of New York State shows this type of sequence in the sedimentary structure. fine

12. 12 ? Decrease in particle size. The Catskill delta

13. 13 Water fall Recession The position of a waterfall gradually migrates upstream. Limestone sandstone Less resistant shale or siltstone The water plunging over the falls removes the softer less resistant underlying bedrock. With the supporting rock removed, the overlying more resistant rock cracks off and falls.