Physical Geography - Version 1 Unit 17 Shaped by Rivers & Running Water

Figure The Grand Canyon , Arizona . Image by Jeremy is used under a license . UNIT 17 SHAPED BY RIVERS RUNNING WATER Goals Objectives of this unit Describe a drainage basin and explain the origins of different types of drainage patterns . Explain how streams become graded and how certain geological and anthropogenic changes can result in a stream losing their gradation . Describe the formation of stream terraces . Describe the processes by which sediments are moved by streams and the flow velocities that are necessary to erode them from the stream bed and keep them suspended in the water . Describe the process of stream evolution . GEOGRAPHY

RIVERS Streams are the most important agents of erosion and transportation of sediments on surface . They are responsible for the creation of much ofthe topography that we see around us . They are also locations of great beauty and tranquility , and of course , they provide much of the water that is essential to our existence . But streams are not always peaceful and soothing . During large storms and rapid , they can become raging torrents capable of moving cars and houses and destroying roads and bridges . When they spill over their banks , they can flood huge areas , devastating populations , and infrastructure . Over the past century , many of the most damaging natural disasters in California have been attributed to flowing water , and we can expect them to become even more severe as the climate changes . The Hydrological Cycle Water is constantly on the move . It is evaporated from the oceans , lakes , streams , the surface of the land , and plants ( transpiration ) by solar energy . It is moved through the atmosphere by winds and condenses to form clouds of water droplets or ice crystals . It comes back down as rain or snow and then flows through streams , into lakes , and eventually back to the oceans . Water on the surface and in streams and lakes infiltrates the ground to become groundwater . Groundwater slowly moves through the rock and surficial materials . Some groundwater returns to other streams and lakes , and some go directly back to the oceans . fi I Condensation ' Evaporation I Oceans Ocean cu Dept Sunny award Emu my mini Groundwater storage Figure The Hydrologic Cycle . Image by is in the public domain . GEOGRAPHY

Even while it moving around , water is stored in various reservoirs . The largest , by far , is the oceans , accounting for 97 ofthe volume . Of course , that water is salty . The remaining is freshwater . of our freshwater is stored in ice and is stored in the ground . The remaining freshwater , about of the total is stored in lakes , streams , vegetation , and the atmosphere . Although the proportion of Earth water that is in the atmosphere is tiny , the actual volume is huge . At any given time , there is the equivalent of approximately of water in the air in the form of water vapor and water droplets in clouds . Water is evaporated from the oceans , vegetation , and lakes at a rate of per day , and just about the same volume falls as rain and snow every day over both the oceans and land . The precipitation that falls on land goes back to the ocean in the form of ( 117 ) and groundwater flow ( STREAMS RIVERS Freshwater in streams , ponds , and lakes is an extremely important part of the water cycle if only because of its importance to living creatures . Along with wetlands , these freshwater regions contain a tremendous variety of organisms . Streams are bodies of water that have a current they are in constant motion . Geologists recognize many categories of streams depending on their size , depth , speed , and location . Creeks , brooks , tributaries , bayous , and rivers might all be lumped together as streams . In streams , water always flows downhill , but the form that downhill movement takes varies with rock type , topography , and many other factors . Stream erosion and deposition are extremely important creators and destroyers of and were described in the Erosion and Deposition unit . Parts of a Stream A stream originates at its source . A source is likely to be in the high mountains where snows collect in winter and melt in summer , or a source might be a spring . A stream may have more than one source and when two streams come together it called a confluence . The smaller of the two streams is a tributary of the larger stream . A stream may create a pool where the water slows and becomes deeper . The point at which a stream comes into a large body of water , like an ocean or a lake is called the mouth . Where the stream meets the ocean or lake is an estuary . The mix of fresh and saltwater where a river runs into the ocean creates a diversity of environments where many different types of organisms create unique ecosystems . GEOGRAPHY

Confluence Tri buta ry Estuary Figure Visual Examples of a Confluence , Tributary , Estuary . Image by Lumen Learning , Rivers are the largest types of stream , moving large amounts of water from higher to lower elevations . The Amazon River , the world river with the greatest flow , has a flow rate of nearly cubic meters per second ! People have used rivers since the beginning of civilization as a source of water , food , transportation , defense , power , recreation , and waste disposal . Also , the lowest elevation a stream can flow is its base level , usually the ocean . DI A divide is a topographically high area that separates a landscape into different water basins . The rain that falls on the north side of a ridge flows into the northern drainage basin and rain that falls on the south side flows into the southern drainage basin . On a much grander scale , entire continent has divides , known as the continental divides . CONTINENTAL DIVIDES ARCTIC OCEAN nu , Great Laurentian Arctic Lawrence Eastern Great Basin Figure North American Continental Divide ( Image on Commons by , GEOGRAPHY

DRAINAGE BASINS The drainage pattern is a pattern created by stream erosion over time that reveals characteristics of the kind of rocks and geologic structures in a landscape region drained by streams . The drainage pattern is the pattern formed by the streams , rivers , and lakes in a particular drainage basin . They are governed by the topography of the land , whether a particular region is dominated by hard or soft rocks and the gradient of the land . A watershed represents all of the stream tributaries that flow to some location along the stream channel . The number , size , and shape of the drainage basins found in an area vary , and the larger the topographic map , the more information on the drainage basin is available . The pattern of tributaries within a drainage basin depends largely on the type of rock beneath , and on structures within that rock ( folds , fractures , faults , The main types of drainage patterns Dendritic patterns , which are by far the most common , develop in areas where the rock beneath the stream has no particular fabric or structure and can be eroded equally easily in all directions . Trellis drainage patterns typically develop where sedimentary rocks have been folded or tilted and then eroded to varying degrees depending on their strength . Rectangular patterns develop in areas that have very little topography and a system of bedding planes , fractures , or faults that form a rectangular network . Parallel drainage system is a pattern of rivers caused by steep slopes with some relief . Because of the steep slopes , the streams are swift and straight , with very few tributaries , and all flow in the same direction . Parallel drainage patterns form where there is a pronounced slope to the surface . A parallel pattern also develops in regions of parallel , elongate like resistant rock bands . Radial drainage system , the streams radiate outwards from a central high point . Volcanoes usually display excellent radial drainage . Other geological features on which radial drainage commonly develops are domes and . On these features , the drainage may exhibit a combination of radial patterns . Centripetal drainage system is similar to the radial drainage system , with the only exception that radial drainage flows out versus centripetal drainage flows in . Deranged drainage system is a drainage system in drainage basins where there is no coherent pattern to the rivers and lakes . Angular drainage patterns form where bedrock joints and faults intersect at more acute angles than rectangular drainage patterns . Angles are both more and less than 90 degrees . GEOGRAPHY

( Figure Common Drainage Patterns ( A ) Dendritic , Parallel , Trellis , Rectangular . Image by Ling Zhang and Eric , BY . RIVER TERRACES Sediments accumulate within the flood plain of a stream , and then , ifthe base level changes , or if there is less sediment to deposit , the stream may cut down through those existing sediments to form terraces . In the late century , American geologist William Davis proposed that streams and the surrounding terrain develop in a cycle of erosion . Following tectonic uplift , streams erode quickly , developing deep valleys that tend to follow relatively straight paths . Gradients are high , and profiles are ungraded . Rapids and waterfalls are common . During the mature stage , streams erode wider valleys and start to deposit thick sediment layers . Gradients are slowly reduced and grading increases . In old age , streams are surrounded by rolling hills , and they occupy wide valleys . Meandering patterns are common . I ' Figure River Terraces along the Colorado River In the Grand Canyon , Arizona . Image is used under a license . GEOGRAPHY

Davis work was done long before the idea of plate tectonics , and he was not familiar with the impacts of glacial erosion on streams and their environments . While some parts of his theory are out of date , it is still a useful way to understand streams and their evolution . Initial stage following uplift Mature initial development of flood plain Old age wide flood plain little erosion Figure A depiction of the Davis cycle of erosion a initial stage , youthful stage , mature stage , and a old age . Image by Steven ( 2015 ) is used under a BY license . STREAM EROSION DEPOSITION Flowing water is a very important mechanism for both erosion and deposition . Water flow in a stream is primarily related to the stream gradient , but it is also controlled by the geometry of the stream channel . Water flow velocity is decreased by friction along the stream bed , so it is slowest at the bottom and edges and fastest near the surface and in the middle . The velocity just below the surface is typically a little higher than right at the surface because of friction between the water and the air . On a curved section of a stream , flow is fastest on the outside and slowest on the inside . A cut bank is the outside bank of a stream , which is continually undergoing erosion . Cut banks are found in abundance along mature or meandering streams , they are located on the outside of a stream bend . They are shaped much like a small cliff and are formed by the erosion of soil as the stream collides with the riverbank . As opposed to a point bar which is an area of deposition , a cut bank is an area of erosion . A point bar is a depositional feature made of sediment that accumulates on the inside bend of streams . Point bars are found in abundance in mature or meandering streams . They are and located on the inside of a stream bend . GEOGRAPHY

Fastest flow Slowest flow Figure The Velocity ofa Stream depends on whether the Channel is Straight or Curved . Image by Steven , BY . Other factors that affect velocity are the size of sediments on the stream bed because large particles tend to slow the flow more than small ones and the discharge , or volume of water passing a point in a unit of time ( During a flood , the water level always rises , so there is a greater area for the water to flow in however , as long as a river remains confined to its channel , the velocity ofthe water flow also increases . Large particles rest on the bottom , and may only be moved during rapid flows under flood conditions . They can be moved by saltation ( bouncing ) and by traction ( being pushed along by the force of the flow ) Smaller particles may rest on the bottom some of the time , where they can be moved by saltation and traction , but they can also be held in suspension in the flowing water , especially at higher velocities . As you know from intuition and experience , streams that flow fast tend to be turbulent ( flow paths are chaotic and the water surface appears rough ) and the water may be muddy , while those that flow more slowly tend to have laminar flow ( flow and a smooth water surface ) and clear water . Turbulent flow is more effective than laminar flow at keeping sediments in suspension . Stream water also has a dissolved load , which represents ( on average ) about 15 ofthe mass of material transported and includes ions such as calcium ( Ca ) and chloride ( in solution . GEOGRAPHY

Particles in suspension and ions in solution Figure Modes of Transportation Dissolved Ions . Image by Steven , BY . The faster the water is flowing , the larger the particles that can be kept in suspension and transported within the flowing water . However , as Swedish geographer discovered in the , the relationship between grain size and the likelihood of a grain being eroded , transported , or deposited is not as simple as one might imagine . Consider , for example , a grain of sand . If it is resting on the bottom , it will remain there until the velocity is high enough to erode it , around 20 . But once it is in suspension , that same particle will remain in suspension as long as the velocity does drop below 10 . For a 10 gravel grain , the velocity is 105 to be eroded from the bed but only 80 to remain in suspension . mo 17 deposited 10 100 clay silt sand gravel pebbles , cobbles , boulders Particle size ( and type Figure A Diagram Showing the Relationships Between Particle Size Velocity . Image by Steven , BY . GEOGRAPHY

On the other hand , a silt particle only needs a velocity of to remain in suspension but requires 60 to be eroded . In other words , a tiny silt grain requires a greater velocity to be eroded than a grain of sand that is 100 times larger ! For particles , the discrepancy is even greater . In a stream , the most easily eroded particles are small sand grains between and . and anything smaller or larger requires a higher water velocity to be eroded and in the flow . The main reason for this is those smaller particles , and especially the tiny grains of clay , have a strong tendency to stick together , and so are difficult to erode from the stream bed . It is important to be aware that a stream can both erode and deposit sediments at the same time . At 100 , for example , silt , sand , and medium gravel will be eroded from the stream bed and transported in suspension , coarse gravel will be held in suspension , pebbles will be both transported and deposited , and cobbles and boulders will remain stationary on the stream bed . A stream typically reaches its greatest velocity when it is close to flooding over its banks . This is known as the stage . As soon as the flooding stream its banks and occupies the wide area of its flood plain , the water has a much larger area to flow through and the velocity drops significantly . At this point , sediment that was being carried by the water is deposited near the edge of the channel , forming a natural bank or . stage Flood stage Nix , thinner sediments on the material at the channel edge Natural from ' repetitive flooding Figure The Development of Natural During the Flooding ofa Stream . Image by Steven , BY . GEOGRAPHY

Stream Types Stream channels can be straight or curved , deep and slow , or rapid and choked with coarse sediments . The cycle of erosion has some influence on the nature of a stream , but there are other factors that are equally as important . Youthful streams that are actively down cutting their channels tend to be relatively straight and are typically ungraded ( meaning that rapids and falls are common ) Youthful streams commonly have a morphology , meaning that the stream consists of a series of pools connected by rapids and waterfalls . They also have steep gradients and steep and narrow valleys , in some cases steep enough to be called canyons . Figure Waterfall at Whitney Portal , Lone Pine California . Image by Jeremy is used under a license . In mountainous , such as that in the Sierra Nevada , steep youthful streams typically flow into wide and relatively valleys . The youthful streams have high sediment loads , and when they flow into the glacial valleys where the velocity is high enough to carry all of the sediment , braided patterns develop , characterized by a series of narrow channels separated by gravel bars . GEOGRAPHY

Figure The Northern Owens River , The Direction is Southward , Note the Abandoned Channels ( Mag data 2019 . Mature streams water is stored for later use in natural water sources , such as groundwater aquifers , soil water , natural wetlands , and small artificial ponds , tanks , and reservoirs behind major dams . Storing water invites a host of potential issues regardless of that water intended purpose , including contamination through organic and inorganic means . Mature streams will also introduce a small flood plain , caused by the and removal of material , and the river channel itself will begin to develop shapes , such as meanders and braiding . Braided streams can develop anywhere there is more sediment than a stream can transport . One such environment is in volcanic regions , where explosive eruptions produce large amounts of unconsolidated material that gets washed into streams . The Owens River next to Lone Pine in California is a good example of this . Old age streams are easily identified by their very low gradient , rich meanders , and a plethora of oxbow lakes and meander scars . The depositional process becomes more predominant and begins forming deltas , estuaries , levees , and . This landscape will also have a very broad , or wide , and low erosive energy . Think ofthe mighty Mississippi river . A stream that occupies a wide , flat flood plain with a low gradient typically carries only sized and finer sediments and develops a sinuous flow pattern . When a stream flows around a corner , the water on the outside has farther to go and tends to flow faster . This leads to erosion of the banks on the outside ofthe curve , deposition on the inside , and formation of a point bar . Over time , the sinuosity of the stream becomes increasingly exaggerated , and the channel migrates around within its flood plain , forming a meandering pattern . The meander in the GEOGRAPHY

middle of the photo has reached the point where the thin neck of land between two parts of the channel is about to be eroded through . When this happens , another oxbow lake will form . WATER STO RAG Water is stored for later use in natural water sources , such as groundwater aquifers , soil water , natural wetlands , and small artificial ponds , tanks and reservoirs behind major dams . Storing water invites a host of potential issues regardless ofthat water intended purpose , including contamination through organic and inorganic means . Ponds Lakes Ponds and lakes are bordered by hills or low rises so that the water is blocked from flowing directly downhill . Ponds are small bodies of freshwater that usually have no outlet ponds are often fed by underground springs . Lakes are larger bodies of water . Lakes are usually freshwater , although the Great Salt Lake in Utah is just one exception . Water usually drains out of a lake through a river or a stream and all lakes lose water to evaporation . Figure Photo at Lake Sabrina , Bishop California . Image by Jeremy is used under a license . Large lakes have tidal systems and currents and can even affect weather patterns . The Great Lakes in the United States contain 22 of the world fresh surface water . The largest ofthem , Lake GEOGRAPHY

Superior , has a tide that rises and falls several centimeters each day . The Great Lakes are large enough to alter the weather system in the Northeastern United States by the lake effect , which is an increase in snow downwind of the relatively warm lakes . The Great Lakes are home to countless species of fish and wildlife . Lakes form in a variety of different ways in depressions carved by glaciers , in , and along tectonic faults , to name a few . Subglacial lakes are even found below a frozen ice cap . As a result of geologic history and the arrangement of landmasses , most lakes are in the Northern Hemisphere . More than 60 of all the world lakes are in of these lakes were formed by the glaciers that covered most of Canada in the last Ice Age . Limnology is the study of bodies of freshwater and the organisms that live there . The ecosystem of a lake is divided into three distinct sections The surface ( littoral ) zone is the sloped area closest to the edge of the water . The zone ( also the photic or limnetic zone ) has abundant sunlight . The zone ( also the aphotic or zone ) has little or no sunlight . There are several life zones found within a lake . In the littoral zone , sunlight promotes plant growth , which provides food and shelter to animals such as snails , insects , and fish . In the water zone , other plants and fish , such as bass and trout , live . The zone does not have photosynthesis since there is no sunlight . Most organisms are scavengers , such as crabs and catfish that feed on dead organisms that fall to the bottom of the lake . Fungi and bacteria aid in the decomposition in the deep zone . Though different creatures live in the oceans , ocean waters also have these same divisions based on sunlight with similar types of creatures that live in each of the zones . Lakes are not permanent features of a landscape . Some come and go with the seasons , as water levels rise and fall . Over a longer time , lakes disappear when they fill with sediments , if the springs or streams that fill them diminish , or if their outlets grow because of erosion . When the climate of an area changes , lakes can either expand or shrink . Lakes may disappear if precipitation significantly diminishes . Groundwater Although this may seem surprising , water beneath the ground is commonplace . Usually , groundwater travels slowly and silently beneath the surface , but in some locations , it bubbles to the surface at springs . The products of erosion and deposition by groundwater were described in the Erosion and Deposition chapter . Groundwater is the largest reservoir of liquid GEOGRAPHY

freshwater on Earth and is found in aquifers , porous rock , and sediment with water in between . Water is attracted to the soil particles and capillary action , which describes how water moves through a porous media , moves water from wet soil to dry areas . Aquifers are found at different depths . Some are just below the surface and some are found much deeper below the land surface . A region may have more than one aquifer beneath it and even most deserts are above aquifers . The source region for an aquifer beneath a desert is likely to be far from where the aquifer is located for example , it may be in a mountain area . The amount of water that is available to enter groundwater in a region is influenced by the local climate , the slope of the land , the type of rock found at the surface , the vegetation cover , land use in the area , and water retention , which is the amount of water that remains in the ground . More water goes into the ground where there is a lot of rain , flat land , porous rock , exposed soil , and where water is not already filling the soil and rock . Pumping wells can drawdown the water table Precipitation Pumping well Figure Diagram Showing Water Tables , Wells Flow . Image by is in the public domain . The residence time of water in a groundwater aquifer can be from minutes to thousands of years . Groundwater is often called fossil water because it has remained in the ground for so long , often since the end of the ice ages . To be a good aquifer , it must have good porosity ( small spaces between grains ) permeability ( connections between pores ) and natural recharge by precipitation . The water droplets are found in the pores between the sediment grains , which is porosity . When the water can travel between ores , that permeability . To reach an aquifer , surface water infiltrates downward into the ground through tiny spaces or pores in the rock . The water travels down through the permeable rock until it reaches a layer that does not have pores this GEOGRAPHY

rock is impermeable . This impermeable rock layer forms the base of the aquifer . The upper surface where the groundwater reaches is the water table . The Water Table For a groundwater aquifer to contain the same amount of water , the amount of recharge must equal the amount of discharge . What are the likely sources of recharge ?

What are the likely sources of discharge ?

In wet regions , streams are fed by groundwater the surface of the stream is the top of the water table . In dry regions , water seeps down from the stream into the aquifer . These streams are often dry much ofthe year . Water leaves a groundwater reservoir in streams or springs . People take water from aquifers , too . What happens to the water table when there is a lot of rainfall ?

What happens when there is a drought ?

Although groundwater levels do not rise and fall as rapidly as at the surface , over time the water table will rise during wet periods and fall during droughts . One ofthe most interesting , but extremely atypical types of aquifers is found in Florida . Although aquifers are very rarely underground rivers , in Florida water has dissolved the limestone so that streams travel underground and aboveground . Pin It ! Water Cycle View this water animation the to learn more about parts of the water cycle such as groundwater and aquifers . GROUNDWATER USE Groundwater is an extremely important water source for people . Groundwater is a renewable resource and its use is sustainable when the water pumped from the aquifer is replenished . It is important for anyone who intends to dig a well to know how deep beneath the surface the water table is . Because groundwater involves interaction between the Earth and the water , the study of groundwater is called hydrogeology . Some aquifers are overused people pump out more water than is replaced . As the water is pumped out , the water table slowly falls , requiring wells to be dug deeper , which takes more money and energy . Wells may go completely dry if they are not deep enough to reach into the lowered water table . The Aquifer supplies about of the irrigation water in the United States . The aquifer is found from 30 to 100 meters deep over about square kilometers ! The water in the aquifer is mostly from the last ice age . The Aquifer is widely used by people for municipal and agricultural needs . About eight times more water is taken from the Aquifer each year than is replenished . Much ofthe water is used for irrigation of crops in the Bread Basket of the central plains . Currently , there is great concern about the health of this vast aquifer because it is being tapped into and used at a greater rate than being replenished by natural processes . GEOGRAPHY

This could have huge implications in regard to food production in the country ifthis critical water source is depleted . At current rates of use , 70 of the aquifer could be gone by 2050 . Overuse and lowering ofthe water tables of aquifers could have other impacts as well . Lowering the water table may cause the ground surface to sink . Subsidence may occur beneath houses and other structures . When coastal aquifers are overused , saltwater from the ocean may enter the aquifer , contaminating the aquifer and making it less useful for drinking and irrigation . Saltwater incursion is a problem in developed coastal regions , such as in Hawaii . Springs Wells Groundwater meets the surface in a stream , as shown below , or a spring . A spring may be constant or may only flow at certain times of the year . Towns in many locations depend on water from springs . Springs can be an extremely important source of water in locations where surface water is scarce . A well is created by digging or drilling beneath the surface , to reach groundwater . When the water table is close to the surface , wells are a convenient method for extracting water . When the water table is far below the surface , specialized equipment must be used to dig a well . Most wells use motorized pumps to bring water to the surface , but some still require people to use a bucket to draw water up . Finally , it also important to understand how water is cleaned , filtered , and delivered to our homes and work . Too many of us do not know where our water comes from and we take it for granted . This often leads to the wasteful water use of our lawns , showers , and other appliances . Pin It ! Water Treatment ! View this website for more rules and to learn more about parts of the water treatment and the . GEOGRAPHY

Spring wu Figure An Image Showing Both a Natural Spring Well . Image by , UNIT 17 SUMMARY Water is stored in the oceans , glacial ice , the ground , lakes , rivers , and the atmosphere . Its movement is powered by the sun and gravity . All of the precipitation that falls within a drainage basin flows into the stream that drains that area . Stream drainage patterns are determined by the type of rock within the basin . Over geological time , streams change the landscape that they flow within , and eventually , they become graded , meaning their profile is a smooth curve . A stream can lose that gradation if there is renewed uplift or base level changes for some reason . Youthful streams in steep areas erode rapidly , and they tend to have steep , rocky , and relatively straight channels . Where streams empty into areas with lower gradients , braided streams can form . In areas with even lower gradients , and where silt and sand are the dominant sediments , meanders are common . Deltas form where streams flow into standing water . Water transports material , or load , several different ways saltation , traction ( creep ) dissolved , and suspension . GEOGRAPHY