Streams & Running WaterQuestions to ponderWater our most important compoundPowerPoint PresentationHydrological cycleEarth’s Water BudgetSurface water - streamsAlluvial processWhat is a Stream?How do streams form?Slide 11Slide 12Drainage basinSlide 14Drainage dividesDrainages are separated by DividesSlide 17Slide 18Drainage patterns can tell us about geologyThe four major drainage patternsParts of a streamStream Gradients Larger Gradient = steeper slopesSlide 23Higher gradient = higher erosionHeadward erosion: headward extension of stream channelsSlide 26Stream PiracySlide 28Slide 29Shenandoah RiverSlide 31Streams try to Reach Base LevelStream profileStreams try to reach base levelSlide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Streams & Running WaterStreams & Running WaterLecture 29Lecture 29Questions to ponder•Why are streams such important geological features?•How do streams erode, transport and deposit material?•How does stream profile influence the dynamics of a stream?******on final•What are common features you would expect in a high gradient area? Low gradient area? Near the point of discharge?Waterour most important compound•Controls climate–High specific heat–77% of earth’s surface covered in H2O•Necessary for life•Chemical reactions–Weathering; Chemical sedimentary rocks•Geologic features–Erosion and Deposition of materialHydrologic CycleHydrological cycleP = E + I + RP = PrecipitationE = Evaporation + TranspirationI = InfiltrationR = RunoffEarth’s Water BudgetSurface water - streams•Running water is the major agent of erosion and deposition•Stream networks dominate the Earth’s surface–Humid as well as arid environments•Most significant landform•Critical to Society–Historical uses; modern uses–Transportation, Power, Manufacturing, Agriculture, water supply, etc.Alluvial process•Stream processes are called ALLUVIAL•Material deposited by stream is called ALLUVIUMWhat is a Stream?•A river or stream is any body of water that is flowing downhill in a well defined channel•River systems consist of a main channel and all its tributaries•Streams ultimately discharge into a basin at the MOUTH•Streams can be Perennial or IntermittentHow do streams form?•During rain storms, some water Infiltrates into the soil and ground–Only a certain amount (depending on soil conditions) can be infiltrated. The remainder is Runoff which flows overland•Water on surface then flows down gradient•When overland flow (sheetwash) collects into channels, or erodes channels, streamflow begins.NOT a streamA stream developsWhen flow becomesconfinedParts of a streamTributariesHeadMouthDrainage basin•The area of land that a stream receives its water (the area that is “Drained by that stream”)•Large streams = Large Drainage areas•Small streams or tributaries = Smaller drainage areas•Tributaries bring in water from head water areasTributariesTrunk streamMouthDrainage divides•Usually topographic highs that separate streams and tributaries from one another•Geology plays an important role–Surface geology–Subsurface geologyDrainages are separated by DividesDrainage patterns can tell us about geology•Some rocks are more resistant to erosion than others•Subsurface structures influence drainage•Streams may follow regional fracture patterns•Topography obviously influences stream flow•4 Drainage pattern types: Dendritic, Trellis, Radial & RectangularDendriticRectangularTrellisRadialThe four major drainage patternsParts of a streamTributariesHeadMouthStream GradientsLarger Gradient = steeper slopesMore erosionHigher velocityMore depositionLower velocityGradient = Rise/RunHigher gradient = higher erosion•Thus, streams can rapidly erode at their Headwaters (point where streams originate)•Higher Gradients also give streams a Higher Velocity.Headward erosion: headward extension of stream channelsStream flowStream flowHeadwardHeadwarderosionerosionStream Piracy•Headward erosion can cause streams erode through Drainage DIVIDES and capture and divert the flow of another streamShenandoah RiverStreams try to ReachBase Level•Base level is where the stream discharges•Local Base Level–Lakes, ponds or other streams•Ultimate Base Level–Sea Level (the oceans)•Gives streams potential energyStream profileMore erosionHigher velocityMore depositionLower velocityStreams try to reach base levelHigher Gradient = Higher VelocityAnd ErosionStream dynamics•Strive to reach equilibrium•Balance between erosion and deposition•“Mature” streams develop gentle convex stream profiles•Graded streams – little erosion or depositionGraded Streams•Graded stream - a stream that is balanced between water flow, and sediment erosion and deposition–Changes in the equilibrium condition will change the stream profile•Movement along faults•DamsClassic stream profileBut….•The “classic” profile is rarely achieved•Some streams get close to this equilibrium•ALL streams try to attain it•Structures, Dams, and Geologic processes can change a streams dynamics making it respondStream responds with increased erosionOriginal stream profileDam creates new, local base