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Surface Water

300. Surface Water. Chapter 13. The Role of Streams & Rivers. What role do streams & rivers play on Earth? ~½ of the water that falls to Earth’s surface eventually ends up in a stream or river & most drain to oceans essential part of the water cycle Most important agent of surface erosion.

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Surface Water

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  1. 300 Surface Water Chapter 13

  2. The Role of Streams & Rivers • What role do streams & rivers play on Earth? • ~½ of the water that falls to Earth’s surface eventually ends up in a stream or river • & most drain to oceans • essential part of the water cycle • Most important agent of surface erosion

  3. River Systems • What is a river system? • a river and all of its tributaries • What is a tributary? • a stream that runs into another stream or river

  4. Drainage Basins/Watersheds • What is a drainage basin (or watershed)? • all the land that drains into the river either directly or through its tributaries • Lgst drainage system in U. S. = Mississippi River system Continental Divide Appalachian Mountains

  5. Divides • What is a divide? • high land that separates one drainage basin from another • Continental Divide (Rocky Mountains) is the major divide in the U. S. • rain falling to east flows to (Gulf of Mexico &) Atlantic • by way of Mississippi River system • rain falling to west flows to the Pacific Continental Divide

  6. Stream/River Characteristics: Velocity • What is “velocity”? • distance water travels in a given amount of time • How is velocity measured? • float method • flow meter Measuring Stream Velocity Video

  7. Stream/River Characteristics: Velocity • What affects a stream’s velocity? • amount of energy a stream has • What affects a stream’s energy? • 1. gradient (slope or steepness) • 2. discharge (amount of water) • 3. channel (stream path) • size (width & depth) • shape of the path (straight/curved)

  8. Stream/River Characteristics: Velocity • How is stream velocity related to the size of the particles it can transport? • faster = larger particles

  9. Stream/River Characteristics: Gradient • What is “gradient” • steepness of the slope • gradient = change in elevation change in distance

  10. Stream/River Characteristics: Gradient • What affects a stream’s gradient? • closer to head (source) • steeper • closer to mouth • gentler

  11. Stream/River Characteristics: Gradient • How is gradient related to velocity? • steeper • faster • gentler • slower

  12. Stream/River Characteristics: Discharge • What is “discharge”? • volume of water that passes a certain point in a given amount of time (related to velocity)

  13. Stream/River Characteristics: Discharge • What affects a stream’s discharge? • # (& volume) of tributaries

  14. Stream/River Characteristics: Discharge Youthful • What affects a stream’s discharge? • age of stream • older • more discharge • younger • less discharge Mature Old Age

  15. Stream/River Characteristics: Discharge • What affects a stream’s discharge? • time of year • late winter to mid-summer • greatest discharge • late summer to mid-winter • lowest discharge Mean of monthly stream flow at Peachtree Creek for each month (for the years 1958 to 2002) The January value of 174 cubic feet per second (ft3/s) was computed by averaging the 44 mean January stream flows (1959-2002).

  16. Stream/River Characteristics: Discharge • How is discharge related to velocity? • greater discharge • greater velocity • lower discharge • lower velocity

  17. Stream/River Characteristics: Discharge

  18. Stream/River Characteristics: Channel • What is a stream’s “channel”? • path through which the water flows

  19. Stream/River Characteristics: Channel Youthful • What affects a stream’s channel? • age of stream • older • wider & deeper • younger • narrower & shallower Mature Old Age

  20. Stream/River Characteristics: Channel • How is a stream’s channel related to its velocity? • straight, wide, & deep • small surface area in contact with the water • less friction • faster (especially at center near surface)

  21. Stream/River Characteristics: Channel • How is a stream’s channel related to its velocity? • shallow & winding • large surface area in contact with water • greater friction • slower • fastest on outside of curve

  22. How Streams Weather & Erode Material • mostly mechanical weathering • split rocks due to pounding • abrasion • by “cutting tools”  sand, pebbles, boulders, etc. • rounded & smoothed

  23. How Streams Weather & Erode Material • What is a “pothole”? • Deep, rounded basin • formed when sand, pebbles, & small boulders swirl around in whirlpools & grind into the rocks • What is a “plunge pool”? • basin worn away at the base of a waterfall • formed by the action of falling water and abrasion of churning particles

  24. Stream Erosion • Streams are effective agents of erosion. • gravity pulls water downhill • soil & rock carried with it

  25. Stream Erosion How Streams Transport Materials • What is a stream’s “load”? • eroded rock & soil materials that are transported downstream • transported 3 ways: • 1. solution (dissolved) • 2. suspension (floating) • 3. bed load

  26. Stream Erosion • What are two measures used to describe the ability of a stream to erode materials? • competence • maximum size of particles stream can carry • capacity • total amount of sediment stream can carry

  27. The size and amount of sediment carried by a stream depends on: •velocity (speed of stream) • discharge (volume of water) choice A choice B Which stream carries larger/more sediment?

  28. horizontal sorting in a stream animation deposition patterns Stream Deposition settling rate by size, shape, density animation vertical sorting animation • When a stream flows to base level (lake/ocean), what happens to its energy? • It decreases. • What happens…? • graded (sorted) deposition occurs • largest closest to mouth & smallest farthest out • largest on bottom & smallest on top

  29. Depositional Features • What is a delta? • fan-shaped deposit of silt & clay at mouth of river • forms when river flows into quiet or large body of water & energy decreases • How do the rates of erosion & deposition affect the size of the delta? • If deposition > erosion  delta grows. • If erosion > deposition  delta shrinks. • A river flowing into a delta splits into distributaries. • smaller channels that bring sediment to front of delta

  30. River Valleys: Youthful Streams • What is the gradient of youthful stream like? • steep • How does the river flow? • in a straight line • In which direction does the river erode? • downward • What is the shape of the resulting valley? • V-shaped (a.k.a. canyon, gorge, chasm) • steep, almost vertical sides and narrow bottom • Is the discharge large or small? • small

  31. River Valleys: Mature Streams • What happens to the gradient as a stream matures? • gradient decreases • How does the river flow? • slight curves b/c velocity decreases • In which direction does the river erode? • outward b/c less erosion of bed & more erosion of sides

  32. River Valleys: Mature Streams • What is the shape of the resulting valley? • wider, broad floor, gently sloping walls • Is the discharge large or small? • medium

  33. River Valleys: Old Age Streams • What happens to the gradient in an old age stream? • gradient decreases to almost horizontal (stream approaches base level) • How does the river flow? • wide meanders across floodplain • can form oxbow lakes • In which direction does the river erode? • outward b/c less erosion of bed (bottom) & more erosion of sides

  34. River Valleys: Old Age Streams • What is the shape of the resulting valley? • valley floor widens into a floodplain • Is the discharge large or small? • large

  35. Life of a Stream Youthful Mature Old Age

  36. Stream Flow, Erosion, & Deposition • Why does water move faster in center? • less friction • What does the profile of a straight section of a stream look like? Slow Fast Slow Slow Fast Slow ------------ Slow

  37. Stream Flow, Erosion, & Deposition • What happens when a stream meanders? • erosion in some areas • cut banks • deposition in other areas • point bars

  38. Stream Flow, Erosion, & Deposition • What does sediment size tell us? • large  water moving fastest (only lg sediments left behind) • small  water slowed down (& dropped small sediments) • point bar • deposition of small sediments • shallow -------------- • cut bank • erosion of small sediments, large sediments left behind • deep Cross-section on next slide

  39. Stream Flow, Erosion, & Deposition • In a meander where does water move fastest? • outside of bend • In a meander where does water move slowest? • inside of bend • What does the profile of a meandering stream look like? slow fast point bar deposition shallow cut bank erosion deep

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