Reading MaterialImpact of sea-level rise on fluvial and glacial valleysPowerPoint PresentationTypes of EstuariesSlide 5Slide 6Estuarine SedimentationSlide 8Sediment TransportSlide 10Slide 11Estuarine CirculationSlide 13Particle FlocculationSlide 15Turbidity MaximumSlide 17River DeltasSlide 19Slide 20Slide 21Location and Shape of DeltasSlide 23Slide 24Deltaic SedimentationSlide 26Slide 27Slide 28Slide 29Examples of Word QuestionsSlide 31Examples of Sentence QuestionsSlide 33Reading MaterialOn reserve in:Ocean-Fisheries library (Oceanography Teaching Building)Through the following web site:https://eres.lib.washington.edu/eres/coursepage.aspx?cid=4291&page=docs\\Type in your UW Net ID when prompted and accept the Copyright statement.“The Estuarine Environment”, from “The World Ocean”W.A. Anikouchine and R.W. Sternberg, Prentice-Hall“River Deltas”, from “The Coast of Puget Sound”J.P. Downing, Puget Sound Books“River Deltas”, from “Coasts”R.A. Davis, Prentice-HallImpact of sea-level rise on fluvial and glacial valleys20,000 y to 7,000 y agovalleys flooded, all sediment trapped7,000 y ago to presentif little sediment supply – estuaries and fjords still fillingtrapping mechanisms very important(Chesapeake Bay)if moderate sediment supply – estuaries nearly fullsome sediment leaks to continental shelf(Columbia River)if much sediment supply – estuaries full and sediment overflowingdeltas build seaward(Mississippi Delta)Chesapeake and Delaware BaysCoastal-Plain EstuariesDrowned river valleysTypes of EstuariesCoastal-Plain estuary (drowned river valley)V shape in cross section – result of fluvial erosionhorn shape (i.e., triangular) in map view – water floods to topographic contour linesexample: Chesapeake BayFjord (drowned glacial valley)U shape in cross section, deep – result of glacial erosionshallow sill at mouthexamples: high latitudes, Alaska, Scotland, Scandinavia, ChileTypes of EstuariesTypes of EstuariesBar-built estuary (lagoon)sand spit or barrier island encloses embaymentshallowexample: Willapa BayTectonic estuarydown-dropped basin (due to plate tectonics)located near ocean, and seawater floods basin example: San Francisco Bay (not very common)Estuarine Sedimentationrelevant to rivers – end of fluvial processesrelevant to beaches – traps or releases sediment to beachSand supplied by rivers (10%)transported as bedloadtrapped near head of estuarywhere gradient of river surface goes to zero (sea level)Mud supplied by rivers (90%)transported as suspended loadtrapped throughout estuarycritical processes: water circulation particle flocculationDistinction between particle transport as bedload and suspended loadNote that “saltation” is intermediate between bedload and suspended loadSediment TransportBedloadgravel = >2 mm sand = 2 mm to 0.064 mm (or 64 microns)particles bounce and roll along bottomrelatively slow means of transporterosion depends on particle sizeSuspended loadsilt = 0.064 mm to 0.004 mm (64-4 microns)clay = <0.004 mm (<4 microns)particles float with waterrelatively fast means of transporterosion depends on particle size and degree of consolidationErosion curve for different grain sizesVelocity necessary to erode gravel and sand depends on grain sizeVelocity necessary to erode silt and clay depends on size, but also the degree of consolidationConsolidation = how much water has been removed from between particlesEstuarine CirculationSalt wedgeEstuarine CirculationSalt wedgefresh water at surface moving seawardboundary with underlying salt water = haloclinefriction with salt water, causes mixingsome salt water carried seaward with fresh waternew salt water moves landward, near bottomtherefore, landward bottom current = salt wedgeFjord circulationshallow sill inhibits exchange of deep wateroxygen is consumed by animals in deep water behind sillanoxia (absence of oxygen) can develop, and animals dieFjord CirculationDeep sillShallow sillthorough mixing of deep waterpoor mixing of deep waterParticle FlocculationFlocculation = formation of aggregates from groups of silt and clay particlesElectrical charges at surface (due to breaks in mineral structure)mostly negative chargesfresh water - particles repel each otherbrackish/salt water – particles attracted to each other form flocsFlocs are larger than particles and sink fasterSilt and clay particles have platey shapeparticles join end to face, forming “card-house” structuresediment reaches bed of estuary with much water within flocs(ultimately leads to consolidation of delta surfaces)Floc CharacteristicsIndividual silt and clay particles are platey in shapeFlocs are formed with “cardhouse” structureWater separates particlesBed deposit initially has much space filled with waterTurbidity MaximumTurbidity = sediment in suspensionFluvial suspended particles carried seaward in surface waterthey flocculate and sinkEstuarine suspended particles carried landward in bottom waterThey meet at the halocline and cause highest turbidity in estuarythis is the turbidity maximumBase of turbidity maximum is where most particles deposit on bedLocation of turbidity maximum moves upstream and downstream:over hours, due to tidesover months, due to seasonal changes in water dischargeUltimately, muddy sediment deposits over most of estuaryESTUARIES ARE EXCELLENT SEDIMENT TRAPSEstuarine CirculationRiver DeltasEvolve from coastal-plain estuariesRivers with much sediment filled their estuaries during the past ~7000 ysea-level rise was slowestuaries are excellent sediment trapsInfilled estuaries have triangular shape = Greek letter Δfrom shape of Nile DeltaSediment supply must be able to overcome:slow rise in sea leveltectonic subsidenceerosion by tides, waves, currentsconsolidation of sediment accumulatingNile DeltaFlowing northward into Mediterranean SeaTwo primary distributaries todayWaves rework shoreline into cuspate shapeActive portion of Mississippi DeltaThe shape is a bird-foot deltaSedimentation is associated with individual distributary channelsThese form because tidal currents are very weak and waves are generally very smallGlobal Distribution of DeltasLocation and Shape of DeltasDeltas found many places in worldmost common where river with much sediment enters protected settinge.g.: small body of water (Mediterranean Sea, Gulf of Mexico, Puget Sound)behind island or reef (Trinidad, Great Barrier Reef)behind seasonal sea ice (Bering Sea, Arctic Ocean)Where river reaches sea level, it
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