Hydrologic cycleStreams- alluvial processes• 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 Intermittent• How 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.Alluvial; alluvium• Stream processes are called ALLUVIAL• Material deposited by stream is called ALLUVIUMTypes of streams: parts of streams (Head, mouth, stream profile, channel, floodplain, valley, tributary, distributary, mouth, delta)- Braided streams- Meandering - Graded stream - a stream that isbalanced between water flow, andsediment erosion and depositiono Changes in the equilibriumcondition will change thestream profile Movement alongfaults Dams- Know the chart on down gradient Drainage 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 areasDrainage patterns (trellis, dendritic, rectangular, radial) and what they mean• 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: 1.Dendritic, 3.Trellis, 4.Radial & 2.RectangularStream piracy• Headward erosion can cause streams erode through Drainage DIVIDES and capture and divert the flow of another streamheadward erosion headward extension of stream channelsCompetence versus capacity• 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 VelocityDischarge; Q=VxA• DISCHARGE – the volume of water a stream moves at a given point• Measured as Volume/time• Volume = Cubic length• Stream Discharge (Q) is measured by:Q = A x VA = Cross sectional area of stream (length2)V = Stream velocity (Length/time)Load – bed load, suspended load, dissolved load; saltation•Load – material carried by stream–Types of stream load•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 sediment•Bed load-(coarse particles) 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 load•Dissolved load (ions in solution)- 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 loadsV-shaped valleys; U-shaped valleys’ Broad U shaped valleys – how/why these occur and how related to energy and stream profile. Features and characteristics of the various valley shapes- V-Shaped Valleyo Numerous rapids and waterfallso Extensive downcutting (erosion)o Minimal deposition of sedimento Stream course is more-or-less o Straight No Floodplains- U-Shaped Valleyo Few if any rapids and waterfallso Side Cutting is dominant erosiono Sediments deposited on floodplaino Streams meander (width of meander belt = width of floodplain)- Broad U-shaped Valleyo No rapids and waterfallso Side cutting is extensiveo Extensive floodplain depositso Width of floodplain is many times the width of the meander beltMeandering streams – spoon-shaped channel profile. How/why of meandering streams.• Very low gradient• Sidecutting produces “bends” in stream path• The sinuous curves of stream are called MEANDERS• Meanders form from lateral erosion, which creates differentials in stream velocitySpoon shaped Channels- Higher energy = more erosion on Cut Bank side- Cut Bank side is deeper- Lower Energy = deposition on Point Bar Side- Point bar side is shallowerCutback, point bar, oxbow(same as cutoff lakes.) - Meanders can be cut off from the stream and form Oxbow LakesCharacteristics of meandering streamsBraided streams• High sediment loads cause stream channels to become choked• Many channels develop• Associated with glacial melts; and dry regionsStream erosion versus deposition features• 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 lengthGroundwater (GW)Porosity; permeability – factors affect these characteristics• Porosity – is the amount of void spaces in rock or soil.– Relates to how much liquid (or gas) geologic material can hold– Percentage of the volume– Affected by the size and shape of particles– Increased by fracturing or dissolution– Decreased by compaction and cementation– Well sorted sediments have higher porosity than poorly sorted sediments • Permeability is the connectedness of these pore spaces– How easily fluids move through geologic material– Permeability is a property of the rock• Controls the ability of water to flow through a rock or soil• Other liquids such as oil flow through rock• Density and viscosity influence flow rateAquifers – confined; unconfined• If Soil or Rock has High Porosity and High Permeability and we can extract usable water it is called an AQUIFER• 2 types• UNCONFINED Aquifers• Open to the surface• Usually defined by the beginning of the Water Table• The depth to the water table varies with response to rainfall• Can be near the surface during wet seasons; Deeper during dry periods• The shape of the water table (and unconfined aquifers) generally follows topography•