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Running water 97.2 % oceans 2.2 % ice

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Presentation on theme: "Running water 97.2 % oceans 2.2 % ice"— Presentation transcript:

1 Running water 97.2 % oceans 2.2 % ice
0.6 % liquid fresh water most of which is ground water Water is always on the move in the water cycle




5 Water Cycle Infiltration = soak in run off - surface flow
evaporation = back into the atmosphere transpiration = back into the atmosphere by plant evapotranspiration - combined

6 Running water Run off begins as sheet flow.
How much goes into the ground depends on the infiltration capacity of the soil Factors of infiltration intensity and duration of rain fall soil wetness(saturation) soil texture slope vegetation

7 Running water Rills - tiny channels Gullies - larger channels
stream - any running body of water sometime called rivers if really large


9 Stream characteristics
Gradient or slope is the vertical drop of the stream over a fixed horizontal distance, The steeper the slope the more energy available for stream flow. Cross-sectional shape determines the amount of drag. The less drag the faster the water can flow Size and roughness also influence drag

10 Stream characteristics
Discharge is the amount of water flowing past a certain point in a given amount of time Discharge (meter 3/ second)= channel width(meters) X depth (meters) X velocity (meters/second)

11 Changes downstream Longitudinal profile - a look at the stream from head to mouth gradient decreases downstream discharge increases downstream width, depth and velocity increase downstream When gradient is high, discharge is small

12 Base level Running water in a stream will erode downward over its course until it reaches a balance point. This balance point is called the base level. Base level is the lowest elevation to which a stream can erode. Two types of base level

13 Base level Ultimate base level - sea level
Temporary ( local) base level - anything which has the capacity to limit downward erosion. Lakes, resistant bedrock, or a larger stream Kalamazoo River Ultimate base level the Atlantic ocean Local base level Lake Michigan

14 Base level Base level can be changed.
Raised base level results is velocity dropping and deposition begins up stream. Lowered base level results in velocity increasing and erosion increasing. How do you raise base level? Build a dam. How do you lower base level? Uplift the land or lower sea level.

15 Base level Sooner or later a stream will reach base level and be neither eroding or depositing just transporting. A graded stream is at base level

16 Stream Erosion Waters in streams are turbulent. They whirl and eddy.
The material in streams (sand, gravel, silt, and clay sized particles, plus dissolved minerals) abrades the streambed and become rounder and smoother with transport. This is called the load. Potholes are gouged by gravel caught in an eddy.

17 Stream Transport Dissolved load - minerals dissolved by ground water and added to the stream. Suspended load - usually the largest load of a stream. Fine sand, silt and clay sized particles. How much suspended sediment depends on velocity of the stream and settling rate of the sediment.

18 Stream Transport Bed Load - the material on the stream bed too large to be carried by suspension. This is the stuff that does the grinding to produce downward erosion. This material moves by rolling, sliding and saltation. Saltation is jumping or skipping down stream

19 Stream Transport The ability to carry material is measured in capacity and competence. Capacity is the maximum load a stream can carry. Competence - the maximum sized particle a stream can carry. The greater the stream’s discharge the greater the capacity and competence.

20 Stream deposition When velocity slows the stream can no longer carry its load. Particles will be deposited by size with the largest settling out first. This sorting explains why particles of the same size are found together. Alluvium is the term for all stream deposited sediments

21 Stream deposition - channel
Channel deposits - the materials deposited mid-stream usually sand or gravel in bars. Point Bars form in the inside bend of a stream meander. Braided streams have bars mid channel. Merger of two streams with different velocity, after glacial melting, or after heavy down pour.

22 Stream deposition- floodplain
Floodplain - the area adjacent to a stream that is covered with water during a flood. Natural levees flank the stream and are an accumulation of gravel deposited during a flood when the water lost it competence and capacity upon leaving the channel.


24 Stream deposition- floodplain
Some levees are so high that tributary streams can’t enter the main stream. These streams (Yazoo tributaries ) flow along the flood plain of the larger stream in swampy (back swamp) poorly drained areas.


26 Stream deposition- Fans and Deltas
When a stream loses its competency abruptly it will drop its load. Alluvial fans will form if the deposition occurs on land. These are fairly steep. Delta will form if the deposition occurs under water.These are fairly shallow.


28 Stream deposition- Fan
Alluvial fans form when a high gradient stream in a narrow mountain valley enters a broad flat basin. The change is gradient is drastic resulting is immediate deposition. Coarse material is deposited at the top of the fan while finer material is carried lower.


30 Stream deposition- delta
Deltas form when a stream enters a lake or the ocean.

31 Stream deposition- delta
The main stream will become sediment choked, so it will seek a higher gradient route to base level. It may do so by splitting into branches called distributaries.


33 Stream deposition- delta
Mississippi River Delta - a bird-foot delta. This delta extends far out into Gulf of Mexico . Many Smaller sub deltas have grown since the ice age. Threat to the Mississippi includes a potential capture and diversion of water further upstream. Could spell disaster for New Orleans.

34 Stream Valleys Playfair’s law - all streams have a main trunk, fed by branches and have carved the valley in which they exist. Two types of stream valleys narrow V shaped valleys wide valleys with flat floors

35 Stream Valleys - V shape
Characterized by downcutting narrow canyons with steep wall rapids and waterfalls Valley walls undergo weathering and mass wasting at the top to help with the profile.

36 Stream Valleys - Wide valleys
More common in a graded stream Erosion shifts from down-cutting to lateral. Streams flow in floodplain is sweeping bends called meanders. Erosion takes place on the outside of the bend at the cut bank. Deposition takes place on the in side of the bend at the point bar Causes the meander to migrate laterally and downstream



39 Stream Valleys - Wide valleys
Sometimes one meander will cut off another to create a shorter channel The abandoned meander is called an oxbow lake. Eventually the lake fills with sediment to create a cut off scar Incised meanders- form when there is a rapid change in base level.



42 Drainage networks All streams drain to an ocean.
The drainage basin is all the land contributes water to the stream. A divide is the imaginary line that separates two drainage basins. Individual drainage basins have one of four patterns depending on the material on which they flow.

43 Drainage Patterns Dendritic - the most common - tree like branches emptying into larger trunks Radial - like spokes on a bike tire draining the side of an isolated cone or dome. Rectangular - flowing over jointed rocks making sharp right angle turns trellis - also rectangular but looking more like a trellis with lots of branches.


45 Stream Piracy - Ahrg!! Streams erode headward, downward and laterally.
As Niagara Falls erodes it is doing so up stream (headward erosion) When the headward erosion of one stream breaches the divide it can divert water from a slower stream. This is stream piracy.


47 Floods and Flood Control
What causes floods? Too much water from rain or melt water. Controls include building artificial levees, dams,channelization (dredging) and better flood plain management (non-structural controls).


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