River/Stream Erosion Notes

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Laureen Doyle
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1 Name Date ES per Mr. Williams River/Stream Erosion Notes Erosion: the of weathered material. FACT: Running water moves more sediment than ANY other type of erosion. 1. The Water Cycle What happens when precipitation falls to Earth s surface? 1) Some 2) Some infiltrates into the ground and becomes 3) Some becomes Read the definitions below, and then label the diagram with the appropriate terms. Accumulation - the process in which water pools in large bodies (like oceans, seas and lakes). Condensation - the process in which water vapor (a gas) in the air turns into liquid water. Condensing water forms clouds in the sky. Water drops that form on the outside of a glass of icy water are condensed water. (This term appears twice in the diagram.) Evaporation - the process in which liquid water becomes water vapor (a gas). Water vaporizes from the surfaces of oceans and lakes, from the surface of the land, and from melts in snow fields. Precipitation - the process in which water (in the form of rain, snow, sleet, or hail) falls from clouds in the sky. Subsurface Runoff - rain, snow melt, or other water that flows in underground streams, drains, or sewers. Surface Runoff - rain, snow melt, or other water that flows in surface streams, rivers, or canals. Transpiration - the process in which some water within plants evaporates into the atmosphere. Water is first absorbed by the plant's roots, then later exits by evaporating through pores in the plant.

2. What determines whether precipitation becomes runoff

1) Gradient 2) Stream discharge (the amount of water in

2 2. What determines whether precipitation becomes runoff or groundwater?. Ground Conditions: 1) Saturated vs. unsaturated 2) Vegetated vs. non-vegetated 3) Gradient When Runoff becomes confined to a channel, a stream exists: 3. What factors affect stream/river velocity? 1) Gradient 2) Stream discharge (the amount of water in the channel) 3) Stream channel shape Factor 1: When gradient, velocity. Think Mountains vs. Plains. Mountain stream Plains Stream

3 Factor 2: When discharge, velocity. Think of the Moodna Creek after a heavy rainstorm. All that added water in the stream channel makes it flow mad fast! Moodna Creek, no flooding Moodna Creek, with flooding. Factor 3: Straight channel vs. Meanders (stream/river curves) In a straight channel, velocity is fastest, just below the surface (see location X in the diagram below). This is because the water is forced to slow down due to friction encountered all along the channel (sides and bottom). Also, the atmosphere forces the water to slow down at the surface.

4 In stream MEANDERS, velocity is fastest on the bend, and velocity is slowest along the bend. This is because water flows straight downhill until it hits something that forces it to change direction (think inertia from middle school science). This causes the fastest water to impact the outside bends more strongly. Remember going down that water slide? In those straight channels of the slide, you went straight downhill. When you were forced to turn after hitting a curve, your body was forced up along the outside of the bend. Water does the same thing. Thanks, momentum! Since water moves FASTER along the outside bend of a meander, will occur here. This cuts away at the bank, and the outside bends are therefore called Cut Banks. Very clever. Since water moves SLOWER along the inside bend of a meander, will occur here. This is because as water slows down, it drops heavier sediments it can no longer carry. Inside bends are called Point Bars.

5 Outside bend: faster velocity results in more erosion. This is a Cut Bank. Inside Bend: slower velocity results in more deposition. This is a Point Bar. Formation of an Oxbow Lake: When exaggerated meanders go bad.

Load: stuff dragged along the bottom cause it s too heavy to pick up (larger sand, pebbles, cobbles) ABRASION round, smooth

6 4. How do rivers/streams carry sediment? 1) In solution (dissolved, can t see it) 2) In suspension: stuff carried within the water column (smaller sand, silt, clay) 3) Bed Load: stuff dragged along the bottom cause it s too heavy to pick up (larger sand, pebbles, cobbles) ABRASION round, smooth sediments: 1) Erosion along the river/stream bottoms (the bed) makes sediments constantly bump into/rub against each other 2) This makes them round and smooth 3) This process is called ABRASION and makes sediments look like dis:

5. Life cycle of a stream A Youthful Stream (Upper Course) Narrow V-shaped Downcutting Swift water Steep gradient Erosion is dominant Mature Stream (Middle Course) Lateral Erosion begins Meanders

7 5. Life cycle of a stream A Youthful Stream (Upper Course) Narrow V-shaped Downcutting Swift water Steep gradient Erosion is dominant Mature Stream (Middle Course) Lateral Erosion begins Meanders develop Floodplains develop Gradient decreases Old Age (Lower Course) Wide meanders and oxbow lakes Wide floodplain Little downcutting Low velocity Low gradient Dynamic equilibrium between erosion and deposition

8 Notice the downcutting erosion in the Young stream and the lateral erosion in the Mature and Old Age streams. As the stream gets older, the lateral erosion widens the valley, creating a larger FLOODPLAIN.

6. Watersheds A watershed, or is the area of land

If you dump pollution on the ground here, it will

9 6. Watersheds A watershed, or is the area of land that feeds a stream and its tributaries Washingtonville is in the watershed. If you dump pollution on the ground here, it will pollute the which drains to the. You just killed a baby seal. Nice job. What did that seal ever do to you?

Erosion Surface Water. moving, transporting, and depositing sediment.

Erosion Surface Water. moving, transporting, and depositing sediment. + Erosion Surface Water moving, transporting, and depositing sediment. + Surface Water 2 Water from rainfall can hit Earth s surface and do a number of things: Slowly soak into the ground: Infiltration