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Chapter 15 River Systems Slide 2 The Water Mystery: It was the 17 th century before scientists could accurately measure the amount of water received on Earth. How much water does the Earth receive? 5 times more than the rivers can carry---so where is it all? Slide 3 The water is in: Streams and rivers Lakes, oceans and icecaps at the poles In rock below the surface- groundwater Tissues of all living creatures Gas in the air as water vapor Slide 4 Water changes from one form to another---how often? Constantly!! If water is always on the move and changes placeswhat is this called? The water cycle: Slide 5 What is evapotranspiration? The total loss of water from the land, plants, and animals. What is it? The loss of water by evaporation and transpiration. Slide 6 A closer look at transpiration of a plant leaf: Slide 7 What is condensation? When the water vapor rises into the atmosphere, expands and cools. As it cools it becomes more dense and comes back down---precipitation. Slide 8 What kind of condensation is the previous picture called? Precipitation! What are some of the forms it comes in? Rain, sleet, snow, hail, Slide 9 Condensation on a glass: The same concept is truegas cools and becomes more dense forming the liquid state of water once again: Slide 10 What is a water budget? TTTThe difference between how much water falls and how much is used. PPPPrecipitation is our income and the evapotranspiration and runoff are the expenses. SSSSo what factors will affect the Earths water budget? Slide 11 Those factors are: Temperature Vegetation Wind Amount and duration of rainfall What if we get too much precipitation? Slide 12 Maybe not good..... The result is moist soil and possible flooding: Slide 13 What if we do not get enough water? Drought! Slide 14 Local water budgets These change with the seasons and with the geography of the area. Cooler temps would mean less evapotranspiration and warmer months would mean more. Streams would therefore transport more water in cooler months than in warmer months. Slide 15 How much water does the average person use each year in the U.S.? 95,000 Liters (20,890.5 gallons) We use water for just about everything from bathing to playing. 90% of the water used is returned to rivers or oceans as wastewater so it is not clean. Slide 16 Conservation of water: Individuals should conserve water by limiting their water use. Do not waste!!!! Slide 17 Section 2 Stream Erosion Slide 18 Stream Erosion WWWWhat happens if precipitation exceeds evapotranspiration in any given area? YYYYou have the beginning of a river system. Slide 19 How does this happen? Soil gets too wet-- Excess water moves downslope as runoff-- Water erodes the land surface and forms a narrow ditch called a gully Eventually this process of precipitation and erosion will form a developed valley with a permanent stream. Slide 20 Parts of a river system: Tributaries: all of the feeder streams that flow into the main stream. The MississippiRivertributaries Slide 21 What is a watershed? The land from which the water runs off into the streams. Slide 22 The areas that separate watersheds are called divides Slide 23 A channel is the narrow depression that a stream flows downhill in: Slide 24 The edges of a channel are the stream banks Slide 25 The part of the stream channel that is covered in water is the stream bed Of course, this one is dry though. Slide 26 Streams are always causing erosion. This makes the stream larger due to the change in the banks, and etc. as the streams flow. What is stream piracy? Slide 27 When watershed from one stream is captured from another. The captured water is now diverted into the river system of the stream that did the capturing. Slide 28 Stream load The materials carried by a stream. Slide 29 As you could see there are 3 types of stream load: Dissolvedinto the water and unseen but there and being transported by the stream water. Bed load is the larger, coarser stuff like sand and gravel. Suspendedparticles of fine sand and silt. The velocity of the water keeps these particles suspended. Slide 30 Stream discharge: The volume of water moved by a stream in a given period of time--- Faster movement = more stream discharge Slower movement = less stream discharge. Slide 31 A streams velocity also affects the stream discharge-what is velocity? The speed and direction of the water. As you can tell, the speed in the front of the stream is 3Xs the rest of it. Slide 32 Stream gradient The change of the elevation as the stream makes it way down to the lakes or oceans. Slide 33 So gradient is steepness of the stream. This one is a steep gradient and moving fast. Slide 34 This stream gradient is low Slide 35 Evolution of a River channel: How does a river evolve? The load, discharge and gradient may decrease and the erosion power of the stream would therefore decrease and this would affect the evolution of the river channelhow? It would not continue to change. Slide 36 What if the mentioned factors of the river increased? This would cause the river to widen and deepen from more erosion, Therefore....... You would have evolution of a stream and it would become a river. Slide 37 Rivers also evolve-what do they develop? Bends and curves. What do we call the bends and curves? Meanders! Slide 38 Why do meanders form? The gradient of the water decreases and thus the velocity decreases. The river is less able to erode down its bed and so the energy is directed against the banks. This causes erosion on the banks. Slide 39 More... As a river rounds a bend, the velocity of he water on the outside of the curve increase and the fast- moving water on the outside erodes the outer bank, however, the inner bank velocity decreases. This slowing on the inside forms a bar of deposited materials. Slide 40 What forms if this process continues? An oxbow lake! Slide 41 What is a braided stream? WWWWhen multiple channels divide and rejoin around sediment bars. Slide 42 Do braided streams cause erosion? Yes. They are a direct result of a large sediment loadthis means erosion took place to get the sediments into the flow of the stream. Slide 43 Section 3 Stream Deposition Slide 44 Stream Deposition The load of a stream is greatest when a large volume of water is flowing swiftly. Slide 45 Deltas occur when a stream enters a larger body of water The stream deposits the load at the mouth of the stream in a triangular shape. The shape and size of a delta are determined by waves, tides, offshore depths and the sediment load of the stream Slide 46 The Nile River Delta: Slide 47 Alluvial Fan These are fan-shaped deposits that form on land and its tip points upstream. Slide 48 Floodplains-the part of the valley floor that may be covered during a flood. Slide 49 Levees The flooding water loses velocity and deposits its coarser sediment load along the banks of the channel: Slide 50 Are there advantages and disadvantages to floodplains? Yes-disadvantagesa flood and a mess. Yes-advantages-fertile land to farm on and easy access to the river for shipping, fishing and transportation. Slide 51 What do people do about flooding? Build dams Slide 52 Make artificial levees Slide 53 Plant vegetation to prevent erosion Slide 54 Life cycles of Lakes Water from streams can collect and form a lake. This water does not make it to the ocean. Slide 55 Where are most lakes? In high latitudes and mountainous areas. Where does this water come from? Precipitation and the melting of ice and snow. Also springs, rivers, and runoff directly from the surrounding land. Slide 56 Most lakes are short-lived- geologically that is. Why? They lose water and dry up They often fill with sediments-when this happens a bog or swamp may form. Slide 57 Chapter 15--done Quiz 1. list 3 ways to help lessen the problems of flooding. 2. list 3 ways precipitation can reach the ground as. 3. what is a water budget? 4. list 5 ways you can help to save water around your home. 5. what 2 ways are fresh water stored? Slide 58 Quiz continued 6.What is a triutary? 7.What is an oxbow and how do they form? 8. what is a flood plain? 9. what is an advantage of living in a flood plain? 10. what is a disadvantage of living in a flood plain.? Slide 59 A little more 11.What is this, and how did it form? Slide 60 Last one. 12. draw and label all of the parts to the water cycle.