FloodsSlide 2The Hydrologic Cycle The Fate of Precipitation Refer to page 291, 299-304.The Hydrologic Cycle The Fate of Precipitation Refer to page 291, 299-304.The Mississippi River Drainage BasinStreams DefinedStream Gradient Longitudinal ProfileStream Gradient Refer to pages 291-292.Stream Base Level Refer to pages 291-292.Slide 10Stream Erosion Refer to pages 291-295.Stream Erosion Refer to pages 291-295.Stream Gradation or Equilibrium Refer to pages 291-295Stream Gradation or EquilibriumDischarge Refer to page 291The Upstream Headwater regionThe Downstream RegionThe Downstream ChannelThe Dispersing System Refer to page 292.Flooding - an excessive discharge. Refer to pages 299-304.Flooding - an excessive discharge.Types of Floods Refer to pages 302-304.Slide 23Flash FloodsRegional Floods The Great Midwestern Flood of 1993 Refer to pages 325, Case in Point page 345.Regional Floods The Great Midwestern Flood of 1993Slide 27Levee FailureSocietal Responses to Flood HazardsArtificial Levees Refer to pages 329-332.Avulsion Refer to page 330, Case in Point page 342, 344.AvulsionChannel ModificationsFloodwallsMultipurpose Dams Refer to pages 332-333, Case in Point pages 349, 350, 217.Multipurpose DamsRetention PondsFlood Frequency and Recurrence Interval Refer to pages 304-309.Flood Frequency and Recurrence IntervalSlide 40Flood Frequency and Recurrence Interval Refer to pages 304-309.Problems with Recurrence Interval Refer to pages 304-309.Floodplain Management Refer to pages 334-337, Case in Point page 351.Floodplain ManagementUrbanization Increases Flooding Refer to page 326.Monitoring the Progress of Storms1FloodsChapter 11Streams and Flood ProcessesRising WatersChapter 12Floods and Human InteractionsFloods2•Flooding of streams is one of the more common and costly types of natural disasters in the U.S.•Account for one-quarter to one-third of annual disaster dollar losses.•Account for 80% of the annual disaster deaths.•The most common cause of flooding is PRECIPITATION •Weather patterns determine precipitation. –Area over which the rain falls–Duration of the rain–IntensityRefer to pages 299-304.The Hydrologic Cycle The Fate of PrecipitationRefer to page 291, 299-304.3Water enters the atmosphere through evaporation. Through precipitation water falls either directly into the ocean or onto the land. Water that falls onto land enters streams by:•Infiltration–The movement of water into rocks or soil through cracks and pore spaces•Runof–Water that flows over the landThe Hydrologic Cycle The Fate of PrecipitationRefer to page 291, 299-304.4How water gets to a stream:The Drainage BasinA cup of land bounded by areas of high relief. Precipitation that falls within the cup of land flows to the stream as Runof over the surface.OrInfiltration and Base flow through the groundwater system.The Mississippi River Drainage Basin5The United States is divided 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.Streams Defined6A body of running water that is confined in a channel and flows under the influence of gravity.Channel width may vary from a few cm’s to several km’s.Stream Gradient Longitudinal Profile 7Stream Gradient - the vertical drop of a channel over a horizontal distance. Refer to pages 291-292.8Stream Gradient Refer to pages 291-292.The headwaters are the upper part of the stream near its source in the mountains. Upstream regions. –Steep Gradient.Lower reaches of a stream are referred to as downstream regions.–Shallow Gradient.9Stream Base Level Refer to pages 291-292.The mouth is the place where a stream channel terminates and enters the sea, a lake, etc.Base level is the theoretical limit to which the stream can erode. It is, in effect, the elevation of the streams mouth.Stream Base Level Refer to pages 291-292.10In general, streams begin at higher elevations, and discharge into other streams and lakes (relative base level) that will eventually reach the ultimate base level (sea level).Stream Erosion Refer to pages 291-295.Potential Energy - energy of position; stored energy.Kinetic Energy- energy of motion; energy to do work.11As potential energy is converted to kinetic energy, the stream performs the work of erosion.The amount of potential energy is proportional to stream gradient.Stream ErosionRefer to pages 291-295.12This spectacular gorge in Colorado is entirely a product of stream erosion acting over several millions of years. Erosion by streams has shaped the land surface worldwide over geologic time. The ability of a stream to erode relates to streamVelocity -- the speed of the water, generally measured in feet per second. Discharge -- the total amount (volume) of water carried by the stream. Discharge is generally measured in cubic feet per second, or cfs.Stream Gradation or Equilibrium Refer to pages 291-29513The volume and velocity of stream flow limit both the size and the amount of sediment that can be carried by the stream.•A stream’s COMPETENCE is the MAXIMUM grain size a stream can transport. Faster moving water has a higher competence because it can move larger sized materials.•The VOLUME of sediment a stream can carry is called CAPACITY. Larger streams (having a larger volume of water) have a higher capacity to transport stuff.Streams will adjust their cross sections and channel gradient to accommodate the stream flow as well as the volume and grain size of sediment supplied to the channel. Changes are insignificant with normal flow or even small floods, and dramatic with large floods.Stream Gradation or Equilibrium14Upstream - Narrow V-shaped channels - high velocity water cuts into stream bed.-High competenceDownstream - wide, deep U-shaped channel - high volumes of water, therefore wide and deep.-High capacityDischarge Refer to page 291The volume of water passing a given point in a stream per unit timeQ = A*v = cross sectional area of the stream channel (depth x width) x velocity measured in m3 or ft3 per second15Upstream - Narrow V-shaped channels-High competenceDownstream - wide, deep U-shaped channel-High capacityThe Upstream Headwater region•The collecting system (high competence)•Steep gradient - high velocity, therefore high erosion•Consist of a network of narrow v-shaped tributary channels that collect water and sediment to the main stream.1617•The transporting system (high
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