4/28/17. #33 Rivers - Principles. Rivers and Civilization

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1 Writing Assignment Due Tonight by 11:59 pm #33 Rivers - Principles See main class web pages for detailed instructions Submit papers in Illinois Compass No copying: Compass will check to see if you have copied sentences or phrases from internet sources or other papers. You MUST write the paper yourself, without borrowing fragments of more than a few words Penalties for plagiarism can be severe Smith River in northwest California Rivers and Civilization Rivers have played huge role in society. Important civilizations have developed around rivers, e.g., Nile River in Egyptian civilization. Nile River and its delta from space Ancient Mesopotamia, cradle of civilization, was located between Tigris and Euphrates rivers Rivers and Civilization Nile River and Pyramid of Cheops River valley civilizations, such as Egypt and Mesopotamia, relied on spring floods that not only provided a convenient source of irrigation water (and drinking water) but also left behind extremely fertile soil for agriculture. Colorado River is used intensively for irrigation Rivers and Civilization Many US cities, including Pittsburgh, St. Louis, New Orleans, are deliberately located along rivers. Gateway Arch and St. Louis are located next to Mississippi River Allegheny, Monongahela, and Ohio Rivers and Pittsburgh New Orleans and Mississippi River 1

2 Rivers have always been used as major transportation routes. Rivers also provide a ready source of food that is, if you re good at catching fish Towboat pushing barges with coal along Ohio River Fly fishing for trout Rivers with dams can provide a relatively clean, reliable, and renewable source of energy, called hydroelectric power. Societal Benefits of Rivers Rivers can provide many recreational opportunities including swimming, boating, fishing, tubing Hoover Dam lies along Colorado River Tubing in Jamaica White water canoeing along Big South Fork of Cumberland River, Tennessee Hazards of Rivers - Floods Along with rivers benefits come hazards, most notably flooding. Rivers can experience quickly developed, devastating floods called flash floods (below) Video of flash flood in Toowoomba, Australia on January 10, 2011 (YouTube, 0:25-3:30, 4-4:10, 5:15-5:30; be.com/watch?v=k YUpkPTcqPY) Hazards of Rivers - Floods Larger rivers: NOT flash floods; floods develop slowly (hours to days) but last longer. Can affect huge areas- e.g., Red River, along borders of Minnesota and the Dakotas, and then into Manitoba, Canada Floodwaters up to mailbox in Moorhead, Minnesota along Red River in 2009 Stillaguamish River in Washington during record flood in

3 River Defined River: Flowing water at Earth's surface usually confined to low area (channel) (vs. lakes, where water doesn t flow much). Confined to channel vs. unchannelized surface run-off, such as flow down driveway or hillside after heavy rainstorm. River - Source of Water and Flow Water derived from rain or snowmelt; moves over land surface or through ground into river. Rivers flow downhill due to pull of gravity, head towards ocean. Tributaries merge to make bigger rivers as water flows downstream. Rouvre River in France s Normandy Region River Sediment Load Material carried by river is its load; includes grains (ranging in size from clay through boulders) carried in suspension or rolled along bottom. With increasing velocity, rivers can carry more sediment load and larger grains. Also includes dissolved load- invisible but important. Big Muddy River, Illinois, has high sediment load Velocity (v) = water speed, 5 km/hour Maximum velocity is in river center, just below surface. Why? Lower velocity along river bottom and sides because friction with stationary channel walls slow river water River - Maximum velocity Streamflow Characteristics - Discharge Discharge (Q) = volume of water passing point over period of time (m 3 /sec or commonly ft 3 /sec). Discharge = v x A = velocity x al area Discharge = velocity x width x depth A = al area of river (m 2 ) River - Cross-Sectional Area width depth Discharge normally increases after rainstorm. Why? Discharge normally increases downstream. Why? (We will use discharge to describe sizes of floods) Increasing v and A Tributaries add to main river 3

4 Clicker Question: Review. Where is the highest velocity of water in this stream? (Assume the river is flowing in a straight line- no curves). River - Maximum velocity Clicker Question: Review. What will happen to the maximum water velocity as the river carries more water and the depth of the water increases? River - Maximum velocity C A B A. It will increase. B. It will decrease. C. It will stay the same. Clicker Question: Review. What will happen to the maximum solid particle size carried by the river as the river carries more water and the depth of the water increases? River - Longitudinal Profile Gradient of river = downhill slope, vertical drop divided by horizontal distance (rise/run) Longitudinal profile: Graph of river s elevation along its flow direction. Major rivers commonly begin in mountains with steep slopes, i.e., large gradients. In this area, sediment grains of all sizes are produced by weathering and erosion, only coarse grains are deposited; medium and fine grains are carried downstream Typical longitudinal profile of river Coarse sediment near river s source A. It will increase. B. It will decrease. C. It will stay the same. River - Longitudinal Profile Farther along, river flows into plains, flat slopes (small gradients). There sand and gravel can be deposited but fine grains carried downstream. Eventually, river empties into ocean or lake, with little to no current and fine grains deposited at mouth of river Sand deposited near river s mouth River Velocity Trends Surprisingly rivers usually increases slightly downstream from mountains into plains. Seems counterintuitive; steep topography should create faster flow than flat topography. Why does maximum river velocity increase downstream? Due to change in size of river channel, small in source area and much larger near mouth. small size of rivers near source means its water is slowed by friction with stationary channel wall Crosssection Fine grains deposited at river s mouth 4

5 River Velocity Trends Maximum velocity of river in plains usually faster than river in mountains due to larger size of river near its mouth larger size of downstream rivers means water in channel middle is not slowed by friction with stationary channel wall River Longitudinal Profile - Effect of Dam Construction Dam construction traps all sediment in reservoir (temporary base level), resulting in upstream deposition and downstream erosion (water has no sediment load), including coastal erosion Mississippi River near Memphis, Tennessee Cross-section Effect of Dam Construction Deposition Dam Erosion Initial profile River Longitudinal Profile - Effect of Dam Construction Water discharged downstream of dam increases downstream erosion; it does not carry sediment to rebuild river bed as sediment moves downstream Kinds of Rivers - Mountain Rivers Several kinds of rivers, emphasizing two: mountain rivers and meandering rivers. Mountain rivers located in mountainous areas near source. In, valleys shaped like letter v, channel occupies nearly all of valley bottom. Typical gradient of mountain river = m/km Yellowstone River in Wyoming Kinds of Rivers - Meandering Rivers Meandering rivers wander back and forth across floodplain, broad, flat area consisting of sediment deposited during flood; associated with broad valleys; bend in river = meander; typical of rivers in plains, near river mouth; typical gradient = 0.1 m/km; photo #1, #2, #3 Migration of River Meanders - Oxbow Lakes Abandoned river meander (oxbow lake) Cuckmere River in England 5

6 Meandering Rivers - Natural Levees Natural levees (sediment buildup parallel to river channel) commonly form due to deposition during flooding (water slows as it overflows channel) Kinds of Rivers - Meandering Rivers Meandering rivers are constantly changing course due to continuous erosion and deposition along meanders. When river changes direction, zone of shifts from middle to outer part (due to inertia), causing erosion there. Inner part of meander has reduced velocity, causing deposition of sand and gravel there. Which direction will meanders on right move over time? right Meanders on left? left Sand deposit on inner part of meander, Innoko River, Alaska B C B A A C Clicker Question: Where is the riverbank most likely to be eroding? Clicker Question: Where is the floodplain? D = A + B + C Migration of River Meanders Meander swings can get so exaggerated that river eventually cuts straighter channel path, leaving abandoned river meander (oxbow lake) Photo #1, #2 Migration of River Meanders - Oxbow Lakes Abandoned river meander (oxbow lake) 6

7 Migration of River Meanders - Oxbow Lakes Meander scars and oxbow lakes in floodplain of Rio Negro River, Argentina Migration of River Meanders - Property Damage Meandering rivers are dynamic systems that are constantly changing their course. So, if you build a house nearby, don't expect river pathway to be constant over time January, 1965 Two months later Drainage Basin Area drained by a river and its tributaries = drainage basin (watershed), can be big or small; high ground separates one drainage basin from another, e.g., drainage divide, continental divide (separates flow to different oceans) Dendritic Drainage Pattern Pattern of river and its tributaries often looks like veins of leaf; called dendritic drainage pattern Dendritic drainage pattern of Yarlung Tsangpo River, Tibet, seen from space: snow cover has melted within valleys. Continental divides of North America Delta When river enters ocean or lake, little to no current, get deposition of sediment load. Llandform of deposited sediment at river mouth = delta. In map view, shape of delta is often like triangle and Greek letter capital delta (D) Satellite photograph of Nile Delta (shown in false color) 7