EARTH SCIENCE: RIVERS 6.1 and 6.2 Unit 13

What is the water cycle and what is meant by it is balanced?

Water constantly moves among the oceans, the atmosphere, the solid Earth and the biosphere. This unending circulation of Earth's water supply is the water cycle. Balance in the water cycle means the average annual precipitation over Earth equals the amount of water that evaporates.The fact that the oceans levels of the world is not changing much indicates the system is balanced.

What are the 3 types of stream loads. Which one accounts for the larges % of the load. Can we see this one? Which load is most responsible for Channel Erosion?

1). Dissolved Load 2). Suspended Load 3).Bed Load Most streams carry the largest part of ther load in suspension. This is a visible cloud of sediment in a river. The particles must be small enough for the velocity to carry. Larger particles can be carried when velocity increases such as when their are storms. Bed Load is most responsible for Channel Erosion-it is a load of solid material that is made up of sediment too large to be carried in suspension. These larger coarser particles move along the bottom of the stream channel eroding the channel.

List and explain the 4 main factors that influence a streams velocity.

1). Shape-A straight and regular shaped stream-less friction higher velocity AND Size-as it increases less friction higher velocity 2), Discharge 3).Roughness of its channel-the rougher-due to boulders etc-more friction-lower the velocity. 4). Gradient-steepness-the steeper more velocity.

Understand the distribution of the Earth's water. What % is available for people to use.

97.2% in oceans. 2.15% in Ice Sheets and Glaciers. .65 divided among lakes, streams groundwater, and the atmosphere. % for People ???

16. What is a stream profile?

A stream profile is a cross-sectional view of a stream from its source, or headwaters, to its mouth--the point downstream where the river empties into another body of water.

17. What is base level? How would lowering base level affect stream erosion

Base level is the lowest point to which a stream can erode its channel. It is level at which the mouth of a stream empties into another body of water. (Ultimate base level and temporary-a lake may be just a temporary obstacle). Lowering the base level is downcutting-can result is incised meanders-winding river in a steep, narrow valley.

21. Be able to determine the boundaries of a watershed? What type of land areas separate watersheds/drainage basins?

Drainage basins are separated by divides: Small Gullies or larger continental divides.

What surfaces favor runoff vs infiltration?

Favors Infiltration: Soil is porous and sandy;rainfall is gentle Favors Runoff: Surface has steep slope; ground is nearly saturated; surface lacks vegetation and is barren.

19. Where do deltas form? Why do they form there?

I. DELTAS - An accumulation of sediment formed where a stream enters a lake or ocean. As a delta grows outward the stream's gradient lessens-water slows down. The channel becomes choked with sediment and water changes direction.

20. What are the two main types of stream valleys?

I. Narrow Valleys - A narrow V-shaped valley shows that the stream's primary work has been downcutting toward base level. (Rapids and Waterfalls) II. Wide Valleys - Stream cuts it channel closer to base level-downward erosion becomes less dominant-energy is directed from side to side making a wider valley.

What is a meander? Where do streams flow faster/slower along a meander?

Meanders=a course with many bends. Longer stretches of straight course streams flow faster-sharper curves slower due to friction. If base level dropped or the land was uplifted the river, which is now considerably above base level, would have excess energy and would down cut it channel. As a result-a winding river in a steep, narrow valley.

Understand how each of the following features would vary between a section of river near the headwaters (high above base level) and a section near the mouth (close to base level): gradient, discharge, valley shape/width, channel characteristics, average velocity at each place, where is erosion focused, sinuosity of channel (straight or meandering), physical features (waterfalls, floodplains, meanders, rapids, oxbow lakes)

Near Headwaters: Gradient: High Velocity is faster Channel size: Small Velocity is slower Channel Shape: Wide and Flat-slow Channel roughness: Very rough - Slow Discharge: Low and velocity slow OVERALL: SLOW Near Mouth: Gradient: Low and V is slow Channel Size: Large V Fast Channel Shape: Deep semicircle V Fast Channel Roughness: Low-Smooth V Fast Discharge: High V Fast OVERALL FAST. Downcutting = V Shaped Valley Meandering=Wide Valley.

18. What are the 3 ways that streams erode their channels?

Streams usually erode their channels lifting loose particles by: 1) abrasion, 2).grinding, and 3). by dissolving soluble material.

In general, where within a river channel is the velocity the highest and why?

The CENTER of the channel is typically where the water flow has the highest velocity (less friction)-when the stream is straight. When it curves it flows to its outer banks.

22. Why is the discharge of the Mississippi River watershed so large?

The Mississippi River has the largest drainage basin in North America. The river and its tributaries collect water from an area of more than 3.2 million square kilometers.

Distinguish between stream discharge and stream load.

The Stream Discharge is the volume of water flowing past a certain point in a given unit of time. Measured in cubic meters. Stream load the amount of sediment the stream carries.

Understand the relationship between particle size carried and water velocity. What factor directly controls the maximum load (Capacity) a stream can carry?

The ability of streams to carry a load is determined by 2 factors: Competence and Capacity. Competence of a stream measures the largest PARTICLES it can transport. A stream's competence increases with it velocity. The competence of a stream increases 4 times-when the velocity doubles. Capacity is the maximum LOAD it can carry. Volume directly controls the capacity-the greater the volume of water in stream the greater the capacity.

What is the most important factor in determining the power of a river to for it to erode and transport material?

The rivers velocity

What energy source drives the water cycle?

The sun and gravity are the forces that start the water cycle.

What is it about water that makes the water cycle possible?

This cycle is possible because water is always changing states.

Know the parts of the water cycle.

Water Cycle: Water EVAPORATES into the atmosphere from the ocean and smaller amount to the land---Winds transport this air until conditions cause it to condense into clouds----PERCIPITATION (rain/snow) falls to Earth. Precipitation that falls into oceans complete one full cycle—the precip that falls to land must make its way back to the oceans---Some soaks into the ground through INFILTRATION---when the land can not absorb any more it flows back to lakes and streams through RUNOFF---it then EVAPORATES back into the atmosphere and when plants absorb the water they release it back through TRANSPIRATION. When precip falls in cold areas it is stored in glaciers-when glaciers begin to melt the water levels of the oceans can increase dramatically.

Under what conditions does deposition occur in a stream? What size sediment is deposited first?

When a stream slows down-its competence decreases and sediment begins to drop out-largest particles first.Deposition occurs as streamflow drops below the critical settling velocity of a certain particle size. The sediment in that category begins to settle out. Streams transport separates solid particles of various sizes-large to small-this is called sorting. Alluvium=material deposited by a stream.