Streams & Running WaterThought-like questionsStream Gradients Larger Gradient = steeper slopesVelocity, Erosion, DepositionPowerPoint PresentationSlide 6Slide 7Slide 8Slide 9Saltation – particles hop, and skipSlide 11Slide 12Slide 13Slide 14Slide 15Slide 16More Transport termsSlide 18Slide 19Slide 20Stream processesSlide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Floodplain developmentSlide 31Slide 32Slide 33Floods – Large Discharge (Q) when a stream over flows its banks and leaves channelSlide 35Slide 36Stream Terraces can develop along floodplainsSlide 38Slide 39Slide 40Alluvial fansSlide 42Streams & Running WaterStreams & Running WaterLecture 30Lecture 30Thought-like questions•How does stream gradient relate to: a) erosion and deposition? B) The sediment size a stream can carry? C) The valley shape of a stream?•What are the types of “load” a stream can carry? How do these different load types move?•Do alluvial fans provide cooling relief from the heat?Stream GradientsLarger Gradient = steeper slopesMore erosionHigher velocityMore depositionLower velocityVelocity, Erosion, Deposition•More material can be carried with higher velocity•Larger particles can be moved with higher velocity•At low velocities, Deposition of material carried by the stream begins•Velocity is dependent upon gradient (and gradient can change along a stream’s path)Stream Flow Dynamics•Load – material carried by stream–Types of stream load•Suspended load (fine particles) •Bed load (coarse particles)•Dissolved load (ions in solution)Stream Flow Dynamics•Suspended Load - fine particles carried long distances suspended in the stream water–Carried along at approximately the same rate as the stream water velocity–Usually the largest fraction of transported sedimentStream Flow Dynamics•Bed Load - particles moved along the stream bed by rolling, sliding, or saltation–Saltation involves coarse particles jumping forward –Bed load moves slower than water velocity–Velocity controls the grain size of the bed loadSaltation – particles hop, and skipStream Flow Dynamics•Dissolved Load is a product of chemical weathering–Primarily composed of seven common ions•Cations - Ca+2, Na+1, Mg+2, K+1•Anions - HCO3-1, SO4-2, Cl-1–Streams that receive large amounts of groundwater have higher dissolved loads–Streams that receive mostly surface run-off have lower dissolved loadsStream Flow Dynamics•Stream water velocity determines the type of flow found in the stream–Low flow velocities - laminar flow–High flow velocities - turbulent flow•Turbulent flow helps keep small particles suspended in the water columnMore Transport terms•Capacity – the maximum volume of Sediment that a stream can carry–Capacity is a function of stream Discharge (Q) which is the volume of water moved for a given period of time•Competence – the largest sized particle a stream can move–Competence is a function of stream VelocityHigher velocityMore competenceLower velocityLess competenceBut, if Q is largeMore capacityCapacityCapacityCompetenceStream processes•Erosion and deposition by streams•Streams erode by either:DOWNCUTTING or SIDECUTTING•Development of stream valleys as erosion proceeds•Development of floodplains as deposition proceeds•Changes in channel shape occur along stream’s lengthMore downcuttingLess downcutting more Side cuttingDowncutting of Channels•Bottom of stream channel abraded by transported sand & gravel–May create steep narrow gorges or potholes–May occur only during high flow due to size of particlesStream characteristics – longitudinal profileV-shaped valleyNumerous rapids and waterfallsExtensive downcutting (erosion)Minimal deposition of sedimentStream course is more-or-less straightNo FloodplainsStream characteristics – longitudinal profileU-shaped valleyFew if any rapids and waterfallsSide Cutting is dominant erosionSediments deposited on floodplainStreams meander (width of meander belt = width of floodplain)Stream characteristics – longitudinal profileBroadly U-shaped valleyNo rapids and waterfallsSide cutting is extensiveExtensive floodplain depositsWidth of floodplain is many times the width of the meander beltFloodplain development•Deep valleys form when streams have high energy to erode as well as transport sediment–V- Shaped valleys•Broad, flat valleys form when streams have little energy to erode but can still transport sediment–U- Shaped valleysLower gradientU-shaped valleysSide cutting is dominantDeposition of sediment during floodingFloodplains develop; some meandersSide cutting is dominant erosionCreates U-shaped valleysDeposition occurs during floodsFloods – Large Discharge (Q)when a stream over flows its banks and leaves channelVelocity decreases when the stream leaves channelSediment is released from waterFloods build Natural Levees of coarse material along banksFine-grained material “blankets” flood plains, creatingBroad, flat areas or swamps and backwater regionsStream Terraces can develop along floodplainsAlluvial fans•Deposition of sediment from Intermittent Streams•Usually where highlands drain into low areas•Form “Fan” shaped deposits•Common in Arid