STREAM SYSTEMS and FLOODS The Hydrologic Cycle Precipitation Evaporation Infiltration Earth s Water and the Hydrologic Cycle Runoff Transpiration The Hydrologic Cycle The Hydrologic Cycle Oceans not filling up Evaporation precipitation System is balanced Earth s Water and the Hydrologic Cycle Runoff is the streams RUNNING WATER Comes from precipitation Transports sediment Erode channels DRAINAGE BASIN Area that drains into a stream Separated by drainage divides Tributaries contribute water to trunk stream Willamette Basin http blog oregonlive com breakingnews 2008 02 large willamette gif THE WORK OF STREAMS Erosion Transportation Deposition EROSION Lifting loose particles Abrasion Dissolution CONTROLS OF EROSION Depends on velocity Gradient Channel characteristics Discharge GRADIENT Slope of channel Vertical drop channel length Stream Gradient Slope of channel along length of stream Changes from head to mouth of stream CHANNEL CHARACTERISTICS Shape Size Roughness Gradient CHANNEL SHAPE Same cross sectional area Channel perimeter about doubled DISCHARGE Volume of water flowing past a point in a certain amount of time Increases downstream Cross sectional area x velocity Gaging station GAGING STATION DISCHARGE CALCULATION http www waterwatch org au library module 4 flow html 10 Willamette Discharge Winter 2006 http waterdata usgs gov or nwis uv format gif period 31 site no 14191000 FLOODS River rises above normal bank retainment Described as Flood Stage Measured in feet above bank full discharge Floods occur periodically due to weather variations Rainfall Snowmelt Uncommon events like landslide or lava dams Willamette Valley 1996 http www bpa gov Power pl columbia 4 gal 2 htm Lake Oswego 1996 http www ci oswego or us engineer images Copyof96 flood 03 000 jpg Willamette Flood http zebu uoregon edu flood3 html RECURRENCE INTERVAL 100 year flood 1 chance of occurrence in a given year 20 year flood 5 chance 500 year flood 0 02 chance Types of Floods Riverine floods Slow events from protracted rainfall Fast events from sudden rainfall Coastal floods Storm surge High tide rainfall Catastrophic floods Flood effects Infrastructure damage Disease Crop and food supply Natural vegetation Flood Control Containment Water management Flood plain building restrictions Levees Pink is levees Brown is hill lines http www mvd usace army mil mrc mrt index php Dams http www bpa gov corporate bpanews library images dams descriptions detroit cfm Flood zone http en tourduvalat org nos programmes observatoires biodiversite et politiques publiques observatoire des zones humi des mediterraneennes Floodplain building plan http www australianecosystems com au projects edgewater estate htm SUMMARY OF CHANGES FROM HEAD TO MOUTH OF STREAM Channel gradient Channel size Discharge Velocity of flow controlled by Gradient Channel shape Discharge THE WORK OF STREAMS Erosion Transportation Deposition TRANSPORTATION Three modes of moving material In solution Dissolved load Suspended load Sliding rolling bouncing Bed load DISSOLVED LOAD From groundwater runoff and channel Supplies ocean with minerals in solution SUSPENDED LOAD Most of material transported Sand silt clay Larger particles in flood BED LOAD Too large to keep suspended Grinds channel and downcuts TRANSPORTATION Competence Capacity COMPETENCE Size of particles Depends on velocity Velocity is proportional to the square of competence CAPACITY Amount of material Depends on discharge Competence vs Capacity Elephant has greater competence Can carry heavier loads Competence vs Capacity Many ants is greater capacity The Work of Streams Greatest competence with greatest velocity Greatest capacity with greatest discharge Maximum during floods The Work of Streams Erosion Transportation Deposition Bedrock Channel High gradient Many rapids and waterfalls http www paul chesterfield btinternet co uk pages landscapes12 htm DEPOSITION Slowing of velocity Largest particles deposited first ALLUVIUM Alluvial Channel High Velocity in Center Velocity displaced around meander curve Channel Pattern Natural progression to more meandering channel character http www ucpress edu books pages 6664 6664 ch04 html Development of meanders http www ucpress edu books pages 6664 6664 ch04 html Development of Meanders http www ucpress edu books pages 6664 6664 ch04 html Channel development Channel development Channel development Formation of Oxbow Lake http www ucpress edu books pages 6664 6664 ch04 html Well Established Meandering Stream http www ucpress edu books pages 6664 6664 ch04 html Channel Pattern High Gradient Highly variable discharge High coarse sediment load Braided channel develops Braided Channel http www ucpress edu books pages 6664 6664 ch04 html Glacial Stream Dart River South Island New Zealand http www bartholmai com NZ2 WebPages 20NZ2 Pages Image51 html http www geology ucdavis edu gel109 SedStructures Lg AKRiverChannel jpg Deposition by Streams Delta Where stream enters standing body of water Velocity slows drops its suspended load Lengthens the stream Distributaries http earth esa int images article archive nile html Glaciers Rivers of ice Moving downslope or out from accumulation center Distinctive erosional and depositional landforms River of Ice http web syr edu bwertl glaciers html Alpine Glacier http www homeralaskacharters com glacier tours htm http www groundtruthtrekking org AKMap php U shaped valley Horns cirques http formontana net striations html Striations Striations 200 Ma ago http www seismo ethz ch kradolfer Angewandte Erdbebenseismologie earth pangaea htm Continental Ice Sheet Greenland http www homepage montana edu geol445 hyperglac morphology1 Antarctica http www homepage montana edu geol445 hyperglac morphology1 http www soils wisc edu courses SS325 primary htm Pleistocene Glacial Impact Outlet glacier http www awi de en news press releases detail item scientists expect increased melting of mountain glaciers
View Full Document
Unlocking...