Sediment Transport Flowing water transports
Description: Sediment Transport Flowing water transports sediment as: Bedload particles roll, slide, or bounce along bottom Suspended load particles carried above bottom by fluid turbulence and grain collisions (dispersive pressure) What is the
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slide1. Sediment Transport<br>
slide2. Flowing water transports sediment as:
Bedload – particles roll, slide, or bounce along bottom
Suspended load – particles carried above bottom by fluid turbulence and grain collisions (“dispersive pressure”)<br>
slide3. What is the significance of grain size? What do sedimentary structures tell us about flow conditions? Controls on grain movement during bedload transport Relationship between bedform type and flow conditions<br>
slide4. What forces act on a sediment grain in moving fluid? Gravity Forces hindering movement Forces promoting movement Fluid Drag Lift Friction and Electrostatic + -<br>
slide5. Gravity Forces hindering movement
Forces promoting movement Fluid Drag FR = m g Resisting force due to inertia: Simply mass × gravity, but grain mass is awkward FR = 4/3 p r3 (rgrain – rfluid) g Replace mass by volume and density FR = Z1 D3 (rgrain – rfluid) g Combine constants into single term Z<br>
slide6. Egrain = ½ V (rfluid) u2 Mass is volume × density FM = Z2 A (rfluid) u2 Energy is force × distance FM = Z2 D2 (rfluid) u2 Gravity Forces hindering movement
Forces promoting movement Fluid Drag Fluid velocity necessary to create moving force:<br>
slide7. At initiation of grain movement, inertia = fluid drag FM = Z2 D2 (rfluid) u2 FR = Z1 D3 (rgrain – rfluid) g Gravity Forces hindering movement
Forces promoting movement Fluid Drag =<br>
slide8. Relationship doesn’t apply at fine grain sizes because Shields’ criterion doesn’t account for friction or electrostatic forces Shields’ Criterion Describes the maximum particle size (D) that can be moved by a current of velocity u – called the competence of the flow – shown by Hjulström diagram For typical river conditions:<br>
slide9. Fluctuating current velocity in natural settings results in alternating erosion and transport with deposition (changing competence and capacity)
This is the main reason why sedimentary rocks are layered<br>
slide2. Flowing water transports sediment as:
Bedload – particles roll, slide, or bounce along bottom
Suspended load – particles carried above bottom by fluid turbulence and grain collisions (“dispersive pressure”)<br>
slide3. What is the significance of grain size? What do sedimentary structures tell us about flow conditions? Controls on grain movement during bedload transport Relationship between bedform type and flow conditions<br>
slide4. What forces act on a sediment grain in moving fluid? Gravity Forces hindering movement Forces promoting movement Fluid Drag Lift Friction and Electrostatic + -<br>
slide5. Gravity Forces hindering movement
Forces promoting movement Fluid Drag FR = m g Resisting force due to inertia: Simply mass × gravity, but grain mass is awkward FR = 4/3 p r3 (rgrain – rfluid) g Replace mass by volume and density FR = Z1 D3 (rgrain – rfluid) g Combine constants into single term Z<br>
slide6. Egrain = ½ V (rfluid) u2 Mass is volume × density FM = Z2 A (rfluid) u2 Energy is force × distance FM = Z2 D2 (rfluid) u2 Gravity Forces hindering movement
Forces promoting movement Fluid Drag Fluid velocity necessary to create moving force:<br>
slide7. At initiation of grain movement, inertia = fluid drag FM = Z2 D2 (rfluid) u2 FR = Z1 D3 (rgrain – rfluid) g Gravity Forces hindering movement
Forces promoting movement Fluid Drag =<br>
slide8. Relationship doesn’t apply at fine grain sizes because Shields’ criterion doesn’t account for friction or electrostatic forces Shields’ Criterion Describes the maximum particle size (D) that can be moved by a current of velocity u – called the competence of the flow – shown by Hjulström diagram For typical river conditions:<br>
slide9. Fluctuating current velocity in natural settings results in alternating erosion and transport with deposition (changing competence and capacity)
This is the main reason why sedimentary rocks are layered<br>