Reading MaterialImpact of sea-level rise on fluvial and glacial valleysSlide 3Slide 4Slide 5Slide 6Slide 7Types of Estuaries Estuary = semi-enclosed coastal environment where freshwater and ocean water meet and mixSlide 9Types of EstuariesEstuarine SedimentationSlide 12Sediment TransportSlide 14Slide 15Estuarine CirculationSlide 17Particle FlocculationSlide 19Turbidity MaximumSlide 21River DeltasSlide 23Slide 24Location and Shape of DeltasSlide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Deltaic SedimentationSlide 34Slide 35Slide 36Slide 37Slide 38Slide 39Reading Material“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-HallEstuaries and DeltasEstuary = semi-enclosed coastal environment where freshwater and ocean water meet and mixDelta = sedimentary deposit at mouth of river that causes coastline to protrude into oceanImpact 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 valleysImpact 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)Some sediment from Columbia River escapes estuary and accumulates on the adjacent continental shelf.Prevailing transport mechanisms carry sediment northward, and most accumulates on the middle shelfImpact 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)Active portion of Mississippi DeltaThe shape is a bird-foot deltaFlooded river valley (estuary) filled, and sediment is (was) building coastline seawardTypes of EstuariesEstuary = semi-enclosed coastal environment where freshwater and ocean water meet and mixCoastal-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 bedload (and suspended load)trapped 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 individual 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
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