GEO 101-007 Chapter 14 Notes
GEO 101-007 Chapter 14 Notes GEO 101-007
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This 4 page Class Notes was uploaded by Jennifer Gintovt on Thursday November 5, 2015. The Class Notes belongs to GEO 101-007 at University of Alabama - Tuscaloosa taught by Dr. William Lambert in Summer 2015. Since its upload, it has received 13 views. For similar materials see The Dynamic Earth in Geology at University of Alabama - Tuscaloosa.
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Date Created: 11/05/15
GEO 101007 102815 Chapter 14 Streams and Floods The Geology of Running Water Water table The boundary approx parallel to the Earth s surface that separates substrate in which groundwater lls the pores from substrate in which air lls the pore Draining the Land Precipitation rain snow hail brings water to land surface Groundwater springs also bring water to the land surface Gravity pulls surface water downhill into a stream channel which is a trough in the surrounding substrate Stream 0 A ribbon of water that ows in a channel Channel 0 A trough dug into the ground surface by owing water 0 Flood 0 An event during which the volume of water in a stream becomes so great that it covers areas outside the stream s normal channel Stream Formation 1 Precipitation rain occurs 2 Sheetwash ows downhill 3 Flowing water digs tiny channels called rills 4 Rills downcut develop into stream ow Headward Erosion The process by which a stream channel lengthens up its slope as the ow of water increases Drainage Network basin An array of interconnecting stream that together drain an area 5 types 0 Dendritic Rectangular Trellis Radial Parallel The geology rock type of land surface is the major control over the type of drainage network that develops O O O O Drainage Divides and Basins A highland or ridge that separates one drainage basin network from another Continental Divide o A highland separating drainage that ows into one ocean from drainage that ows into another GEO 101007 102815 Permanent vs Ephemeral Streams Permanent Streams Ephemeral Streams Water ows all year Do not ow all year Bed oor of channel is at or below Bed oor of channel is above the water table the water table Humid or temperate climates Dry climates o Sufficient rainfall 0 Low rainfall 0 Low evaporation 0 High evaporation Discharge varies seasonally Flows mostly during rare ash oods Stream Discharge Stream Discharge Ekample Discharge area of the stream times average D Ac times Va 111120 m2 stream velocity D 100 m2 x 10 ms Measuring water ow velocity can be difficult 0 Not all water ows through a streamriver at the same speed D 1000 m3s O Laminar Flow Occurs when a uid ows in parallel layers with no disruption between layers Mississippi River 17000 m3s Amazon River 200000 m3s Turbulent Flow A ow regime characterized by chaotic property changes How do streams erode Scouring running water removes loose fragments of sediment Breaking and lifting running water can break clasts of solid rock off the channel oor or walls or may lift clasts of the channel oor Abrasion running water containing sand to gravel size particles acts like sandpaper and grinds away at the channel oor or walls Dissolution running water dissolves soluble minerals as it passes and carries the minerals away in solution Erosion Efficiency of erosion is a function of velocity volume and sediment content of water 0 Small volume slowmoving clear water I Not efficient at erosion 0 Large volume fastmoving turbulent sandy water I Very efficient at erosion o A lot of erosion can occur during a ood more energy How do streams transport sediment GEO 101007 102815 Geologists refer to the total volume of sediment carried by a stream as its sediment load The sediment load consists of 3 components 0 Dissolved load water seeping through rock surrounding stream channel dissolves certain minerals and transports these ions down the stream 0 Suspended load small solid particles silt or clay size that swirl along in the water without settling to the oor of the channel 0 Bed load larger solid particles sand pebbles or cobbles that bounce or roll along stream oor Stream Competence vs Capacity Stream Competence refers to the maximum particle size a stream can carry Stream Capacity refers to the total quantity of sediment it can carry depends on competence and discharge Sediment Deposition High energy fast moving water sediment erosiontransportation Low energy slow moving water sediment deposition Typically streamriver energy decreases slowly When this happens the larger clasts pebbles are deposited first then mediumsize clasts sand and finally small clasts siltclay Sorting occurs Fluvial deposits alluvium sediment deposited in a stream channel along a stream bank or on a oodplain Point bar a wedgeshaped deposit of sediment on the inside bank of a meander m a wedge of sediment formed at a river mouth when the running water of the stream enters standing water the current slows the stream loses competence and sediment settles out Stream gradient The slope of a stream s channel in the downstream direction Longitudinal profile a crosssection image showing the variation in elevation along the length of a river Base Level The lowest elevation a stream channel s oor can reach at a given locality Ultimate base level is sea level sea level can move up and down 0 A lake represents a local base level 0 A stream tries to erode down to base level slow process In general a stream cuts down into the ground in the headwaters and cuts from side to side near the mouth Meander a snakelike curve along a stream s course Alluvial Fan A gently sloping apron of sediment dropped by an ephemeral stream at the base of a mountain in arid or semiarid regions GEO 101007 102815 Braided stream A sedimentchoked stream consisting of entwined subchannels Surface water concerns Flooding Levee failure river pollution