Planet earth stream_powerpoint_presentation

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<ul><li> 1. Fluvial Processes and Flooding</li></ul><p> 2. Summary of Important Concepts </p> <ul><li>Stream erosion is a very important force shaping the earths surface. A streams ability to erode is related to its velocity and its discharge.</li></ul><ul><li>Streams transport sediment particles. Streams that end at standing bodies of water (oceans or lakes) deposit this sediment to form deltas. Intermittent streams in arid mountain areas deposit coarse sediment to form alluvial fans.</li></ul><p> 3. Summary of Important Concepts, continued </p> <ul><li>Flooding is the main hazard associated with streams. Flooding is measured using hydrographs-- graphs which plot water level (or discharge) over a period of time associated with the flood. </li></ul><ul><li><ul><li>Upland floods (upstream)occur in the higher areas of a drainage basin. These are sudden floods (flash floods) that move quickly through narrow valleys.</li></ul></li></ul><ul><li><ul><li>Lowland floodsoccur in the lower areas of a drainage basin. These are slower but longer-lasting floods that spread out over broad areas of the streams floodplain.</li></ul></li></ul><ul><li>Urban development increases flooding because buildings, roads and parking lots decrease the infiltration of rainwater into the ground, and increase the speed with which rainwater runs off into channels. </li></ul><p> 4. Water on Earth is Recycled:The Hydrologic Cycle </p> <ul><li>&gt;97% of earths water is contained in the oceans and roughly 3% is fresh. </li></ul><ul><li>Of that three %, MOST of earths fresh water is tied up in ice (~2%), then groundwater (next chapter), lakes, ice and streams. </li></ul><ul><li>Weather patterns determine the amount and location of precipitation, and the amount and time over which precipitation occurs is not constant. </li></ul><ul><li>Evaluation of Precipitation </li></ul><ul><li><ul><li>Area over which the rain falls </li></ul></li></ul><ul><li><ul><li>Duration of the rain </li></ul></li></ul><ul><li><ul><li>Intensity </li></ul></li></ul><p> 5. The Hydrologic CycleThe Fate of Precipitation </p> <ul><li><ul><li>Most water evaporates off the ocean (large volume) and enters the atmosphere.Through precipitation of snow, rain and ice, water falls either directly back into the ocean or on the land.</li></ul></li></ul><ul><li><ul><li>Water that falls onto land enters streams by infiltration through the ground or by runoff. </li></ul></li></ul><ul><li><ul><li>Infiltration </li></ul></li></ul><ul><li><ul><li><ul><li>The movement of water into rocks or soil through cracks and pore spaces. </li></ul></li></ul></li></ul><ul><li><ul><li>Runoff </li></ul></li></ul><ul><li><ul><li><ul><li>Water that flows over the land. </li></ul></li></ul></li></ul><p> 6. The Hydrologic Cycle 7. How Water Enters a Stream </p> <ul><li>A cup of land bounded by areas of high relief is called the DRAINAGE BASIN.Any precipitation that falls within the cup of land flows to the stream as either runoff or by infiltration.Infiltration capacity of the soil is controlled by: </li></ul><ul><li><ul><li>Slope of the land (steeper slopes cause water to flow as runoff rather than infiltrate). </li></ul></li></ul><ul><li><ul><li>Soil texture (we will see with groundwater, properties of soils may dictate how easily water will infiltratethink about sand versus clay). </li></ul></li></ul><ul><li><ul><li>Nature of the vegetative cover (plants can remove water with roots and transpire the water back into the atmosphere). </li></ul></li></ul><p> 8. The United States is divided, so to speak by the Appalachian Mountains on the East and the Rockies in the Midwest.All water falling in between those two mountain ranges is in the Mississippi River Drainage basin. 9. Streams A body of running water that is confined in a channel and flows under the influence of gravity. Channel width may vary from a few cms to several kms.The term stream in geology refers toany water flowing in a channel , and so includes rivers, streams, creeks, brooks, washes, arroyos and other related features. Throughout this lesson we will use the termstreamto includeallthese types of features. 10. In general, streams begin at theheadwatersat higher elevations, and discharge into other streams and lakes (relative base level) that will eventually reach the ultimate base level (sea level). 11. Streams </p> <ul><li>Longitudinal Profile - Elevation changes of a stream from source to mouth. </li></ul><ul><li>Gradient - the vertical drop of a channel over a horizontal distance. </li></ul><p> 12. Streams </p> <ul><li>Theheadwatersare the upper part of the stream near its source in the mountains.Upstreamregions.</li></ul><ul><li><ul><li>Steep Gradient. </li></ul></li></ul><ul><li>Lower reaches of a stream are referred to asdownstreamregions. </li></ul><ul><li><ul><li>Shallow Gradient. </li></ul></li></ul><p> 13. Streams </p> <ul><li>The mouth is the place where a stream channel terminates and enters the sea, a lake, etc. </li></ul><ul><li>Base level is the theoretical limit to which the stream can erode.It is, in effect, the elevation of the streams mouth. </li></ul><p> 14. The ultimate goal of a stream is to erode the land down to sea level! </p> <ul><li>Streams BEGIN at headwater regions and either DISCHARGE (flow into) into other streams, into lakes or into the ocean. </li></ul><ul><li>The limit to which a stream can downcut the bottom of its channel (erode) is its BASE LEVEL.The ultimate base level for fluvial processes is the ocean (weather all land to sea level).Many streams have a localized base level. </li></ul><p> 15. Stream Gradation </p> <ul><li>Headwater streams are located at higher elevations with steep slopes or gradients (change in elevation/distance).These streams usually have more work (breaking down the mountains) to do in terms of weathering away land and carrying sediments downstream.These streams are termed youthful because they are just beginning to carve the lands surface ( DEGRADING STREAMS ).It is essentially a collecting system for water and sediment. </li></ul><ul><li>As we move further downstream, the land begins to level, slope gradient begins to become more gentle and the water velocity slows down ( GRADED STREAMS ).It is essentially a transporting system for water and sediment. </li></ul><ul><li>Ultimately a stream will discharge into a large lake or ocean.As the stream approaches its base level, the land is relatively flat, water is flowing extremely slow and sediments are deposited into many landforms ( AGGRADING STREAMS ).It is essentially a dispersing system for water and sediment. </li></ul><p> 16. Stream Gradation </p> <ul><li>In order to examine features of these three streams, we need to look at the relationship between stream velocity and how much stuff a stream can carry (i.e. sediment).</li></ul><ul><li>The VOLUME of sediment a stream can carry is calledCAPACITY .Think of the capacity of sediment a stream is capable of carrying.Larger streams (having a larger volume of water has a higher capacity to transport stuff). </li></ul><ul><li>A streamsCOMPETENCEis the MAXIMUM grain size a stream can transport.This is directly related to the velocity of the stream.Faster moving water has a higher competence because it can move larger sized materials. </li></ul><p> 17. </p> <ul><li>Erosionby streams has shaped the land surface worldwide over geologic time. This spectacular gorge in Colorado is entirely a product of stream erosion acting over several millions of years.</li></ul><ul><li>The ability of a stream to erode (competence and capacity) relates to two things: </li></ul><ul><li>Velocity-- thespeedof the water, generally measured infeet per second .</li></ul><ul><li>2. Discharge-- thetotal amount(volume) of water carried by the stream. Discharge is generally measured incubic feet per second , orcfs .</li></ul><p> 18. Stream Velocity Profile: Friction along the bottom and sides of a stream (wetted perimeter) decreases the velocity there.The fastest moving water is therefore, in the center of the stream at the surface. 19. Stream Discharge </p> <ul><li>Stream discharge is the VOLUME of water that passes a given point along a stream in a given amount of time. </li></ul><ul><li>Discharge (Q) depends on two thingshow fast is the water moving (velocity, v) and cross sectional area (A) of the stream (to determine volume of water).</li></ul><ul><li>Q = A*vwhere velocity is measured in feet/sec and area is ft 2 .ft/sec*ft 2 = ft 3 /sec or cubic feet per second or CFS. </li></ul><ul><li>For example, if we have a lot of precipitation, stage level in the stream rises, increasing the cross sectional area of the stream (i.e. more water).Increase A and multiply it by v, will increase the discharge Q. </li></ul><p> 20. </p> <ul><li>Discharge </li></ul><ul><li><ul><li><ul><li>The volume of water passing a given point in a stream per unit time </li></ul></li></ul></li></ul><ul><li><ul><li><ul><li>Q = cross sectional area of the stream channel (depth x width) x velocity</li></ul></li></ul></li></ul><ul><li><ul><li><ul><li>measured in cubic meters or cubic feet per second </li></ul></li></ul></li></ul><p>Upstream - Narrow V-shaped channels Downstream - wide, deep U-shaped channel 21. This graph shows the connection between discharge and the amount of sediment a stream can carry (sediment derived from erosion of the streams banks and channels).The higher the velocity, the faster the water moves, the more sediments can be transported, and the higher erosive capabilities of the stream. A 10x increase in discharge corresponds to a nearly 100x increase in erosion and sediment load carried. 22. Stream Gradation </p> <ul><li>Okay, considering what we have learned, we can examine the features of the different types of streams mentioned earlier.These three types of streams are associated with specific geologic landforms and are located at certain places on land. </li></ul><ul><li>DEGRADING STREAMS are streams that are young, located near headwater areas at high elevations. </li></ul><ul><li>GRADING STREAMS are located down stream of degrading streams (getting closer to sea level)are said to be in equilibrium (Ill address this later). </li></ul><ul><li>AGGRADING STREAMSare located closest to base level at the lowest gradients (very gentle slopes so they move slow).</li></ul><p> 23. Degrading Streams </p> <ul><li>Degrading streams are found in headwater regions with steep gradients.On a map view, the streams appear straight as water is flowing STRAIGHT down hill. </li></ul><ul><li>Steep slopes contribute to faster water velocity and erosion predominates, especially at the bottom of the stream (downcutting). </li></ul><ul><li>The velocity is so rapid that the streams sediment load is less than the streams capacity to carry load (water can transport more sediments than it does).Fast moving water results in a high competence. </li></ul><ul><li>Excessive downcutting results in a V shaped valley with steep valley walls (over time, the valley walls will mass waste into the stream channel, widening the streamworking towards a graded stream system). </li></ul><ul><li>These streams are characterized by rapids and may be associated with water falls.These streams DO NOT have floodplains (flat areas of land adjacent to the stream channel). </li></ul><p> 24. DEGRADING STREAM:Degrading streams at headwater regions effectively erode mountains at higher elevations.Water velocity is the fastest (steep gradient) and erosion most intense.LoadAs erosion of degrading streams continue, the valley walls are widened and deepenedand the land surrounding the stream is less steep.</p> <ul><li>The gentler gradient of graded streams translates into slower velocity of water flow and a shift in capacity to carry sediment typically load equals the capacity to carry sediments so the stream is said to be in equilibrium (overall transporting sediment load). </li></ul><ul><li>Stream energy is directed laterally, where the stream slows down, meanders (an S shaped pattern on a map view)erosion is lateral not at the base of the stream channel. </li></ul><ul><li>Graded stream valley shape is wider, as a result (U shaped). </li></ul><ul><li>Geologic features associated with graded streams include, point bars, cut banks, FLOODPLAINS, levees, oxbow lakes, etc.(View the next few slides). </li></ul><p> 26. GRADED STREAMS:As erosion of a degrading stream continues the valley walls are widened and deepened.Gradient is less steep and stream energy is directed laterally as opposed to vertically (in degrading streams). Load equals the capacity.Sediments are deposited along point bars and eroded at cut banks (I.e. deposition = erosion). 27. As shown by the photo in the previous slide, many streams naturallymeander(form curving, S-shaped bends).Stream channels tend tomeander more and more over time . The reason is becausestreams erode on the outsides of curves(fastest water flow) , and deposit sediment on the insides of curves(slowest water flow).The eroding outside part of the curve is called thecut bank . The inside part of the curve where sediment is deposited is called thepoint bar . 28. Aerial views of graded streams.The squiggly pattern indicates that the gradient is gentle.Typically graded streams have wide U shaped valleys, flood plains and levees.Water velocity is slower and erosion is lateral. 29. This air photo of the Missouri River beautifully shows the mainmeandering channeland the adjacentfloodplain(the band of darker land along the channel).Farms and fields produce the patchy appearance of the floodplain here. The fertile soil of floodplains is intensively farmed throughout the world. Intensive human use of floodplains is one of the problems we will consider later in this lesson. 30. A long-term result of erosion of cut banks (outsides of bends) is that a stream may eventuallycut through the neck of a tight meander , abandoning part of its channel, and forming a feature called anoxbow lake .The figure here shows the steps in this process. 31. Eventually graded streams meander to such an extent that its easier to just cut off the meander (left).The cutoff horseshoe shaped body of water is no longer part of the stream.These are oxbow lakes.See map below. 32. This meander is about to cut off. 33. And when it does, an oxbow lake is left behind.View of several oxbow lakes that have been cutoff from the main stream bottom right.Note the land is relatively flat. 34. And another one.Eventually this lake, being stagnant, will fill in with vegetation.Organisms will proliferate and suck the oxygen out of the water (sediments will turn what color?).As it fills in it will become swampy and then finally land when the water dries/evaporates. 35. OXBOW LAKE This air photo shows anoxbow lake . (The main channel is out of view to the right.) The curving scars on the land show the progressive migration of the meandering channel over time. 36. Aggrading Streams </p> <ul><li>Aggrading streams are considered Old Age.</li></ul><ul><li>Landscape is very flat as we approach sea level. </li></ul><ul><li>The water velocity decreases tremendously at the gentle slopes so that the sediment load exceeds the capacity of the stream to carry it whereby deposition of sediments occurs. </li></ul><ul><li>Massive deposits of sediments produce geologic features called channel bars (filling of the stream channel with sediment) producing a BRAIDED stream pattern on a map view. </li></ul><ul><li>The channel shape is extremely wide and extremely shallow due to the filling in of sediments. </li></ul><ul><li>Generally the main stream valley branches out as it approaches the ocean or large lakethese are called distributaries. </li></ul><p> 37. Downstream near the mouth of the stream, gradients are very low.Load&gt;capacity so much of the sediments are deposited.Water moves very slowly.As sediments deposit, stream channel becomes shallow (sediments fill in).Braided streams heavily loaded with sediment result from channel bars that are deposited.The main channel is lost.Eventually the stream will branch apart into distributaries, right before it discharges into another body of water.These are considered OLD age streams simply because the land is essentially eroded down to base level. 38. The End of the Line </p> <ul><li>Ultimately streams will discharge into a larger body of water (lake or ocean). </li></ul><ul><li>Sediments deposited into the ocean produce a large fan shaped deposit called a delta. </li></ul><ul><li>New Orleans is built on the delta of the Mississippi Rivertechnically, the delta will prograde (grow) out to sea as more and more sedi...</li></ul>