Fluvial GeomorphologySediment TransportDegradationAggradationStream TerracesEquilibriumChannel FormsSuspended LoadBed LoadCauses of DegradationCauses of AggradationGEO 155 1st Edition Lecture 20Last Lecture Hydrology and HydrographsOutline of Current LectureI. Steams as Geomorphic Agentsa. Work That Streams Doi. Sediment Transportii. Degradationiii. Aggradationb. Equilibrium and Changei. Small Scale: Channel Formii. Large Scale: Causes of Degradation and Aggradationc. SlidesCurrent LectureFluvial GeomorphologyThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- How rives shape land formsSediment Transport1. Bed loada. Sediment is too large to be picked up by the stream so it moves along the bottom of the river2. Suspended loada. Particles of rock are carried by the stream, but they are small enough to remain suspended i. The movement of various sizes of the particles is dependent on size and energy of the water body3. Dissolved loada. Rock has been dissolved and carried as solutionDegradation- Valleys formed when streams wear away a landscape downward- GradualAggradation- River deposits alluvium in a valley, which raises the landscape- Valley have flattened bottoms- Alluvium is lose and easy to erodeStream Terraces- Form when flat shells along a valley are revealedo Often times, there are layers of degradation and aggradationo Shows the history of degradation and aggradationEquilibrium- Stream has exactly enough energy to transport the sediment being supplied to it without eroding or depositing any of ito Sediment brought from: Upstream The slopes on either side of the river1. When extra sediment is added to a rivera. There is increased work loadi. Sediment is depositedii. River slope gets steeperb. Increased velocityi. More energyii. Bigger floodsc. Deposition of alluvium stopsi. Works toward equilibriumii. Excess alluvium leveled ofChannel FormsSuspended Load- Narrow and deep river- Particles stay suspended toward the center and toward the surfaceo Unafected by friction- Flows faster- More energyBed Load- At the same river channel, large sediment accumulates at the bottomo Fast moving water from suspended load does not compensate for the additional sediment from bed load- Creates a wide shallow channelo Now capable of moving the bed loadCauses of Degradation - Energy is greater than workloado Land uplift gives water energy to flow downhill Increases energy Bigger floodso Workload is decreased for example by dams Dams backup sediment decreasing the energy of the channel Once the water passes the dam, it is filtered so the energy is increased without any sediment to slow it down- This creates erosion downstream from the damCauses of Aggradation- Workload is greater than the energyo Increased sediment caused by more erosion on the nearby slopeso Decrease energy Smaller floodso Example: at the mouth (intersection) of steep canyons, water passes through; once the stream exits the canyon, it spreads out, slows down, deposits sediment (never in the same location) After repeated floods, a ramp of alluvium is built outside of the canyon known as an alluvium
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