Fluvial Systems Ch 15 Lecture Notes PDF

Fluvial Systems - Ch 15 Lecture #16 November 14th, 2023 Fluvial Processes • Dominant continental land surfaces erosional process, responsible for most sediment transportation. • Other fluid erosional agents are glaciers, waves and wind. • Overland and stream flow erode landscapes and develop river...

Fluvial Systems - Ch 15 Lecture #16 November 14th, 2023 Fluvial Processes • Dominant continental land surfaces erosional process, responsible for most sediment transportation. • Other fluid erosional agents are glaciers, waves and wind. • Overland and stream flow erode landscapes and develop rivers. • Material is transported and deposited by fluvial systems. • Responsible for the formation of most valleys. • Deltas and floodplains are depositional fluvial landforms. Slope Erosion • Infiltration excess overland flow • Saturation overland flow • Hortonian overland flow Runoff Distribution Warm coastal zones Sheet Erosion/Runoff Erosion • • • • Gradient Volume Slope length Soil type/cohesion Accelerated Erosion • Removal of plant cover • By Fire • By Logging • By other disturbance • Rain splash detaches fine particles Rills and Gullies • Torrential rains • Steep slopes • Result is barren topography • Badlands Work of Streams • Stream Erosion • Stream Transport • Stream deposition Stream Erosion Processes • Controlled by the stream velocity 1) Hydraulic action 1) Bank caving 2) Bed friction 2) Abrasion 3) Corrosion •q Giant’s Kettle • Abrasional erosion through the mobilization of cobbles and gravel, grinding the bedrock down. Stream Transport • Stream load 1) Dissolved load 2) Suspension load • Float load 3) Bed load Dissolved Load Hjulström Curve • Relationship between river velocity and particles size. • Demonstrates when they will be: • Eroded • Transported • Deposited Hjulström Curve This Photo by Unknown Author is licensed under CC BY Global Fluvial Sediment Transport • 95% of sediment transported by rivers • 15-20 Gt/yr 16 Global Denudation • 15% chemical weathering • The rest is physical weathering expressed in fluvial sediment transport. 17 Channel Morphology • Channel Gradient • Channel Stability • Sediment caliber • Sediment supply Meandering Stream Formation • Thalweg – fastest water • Helical flow – corkscrew Counter Point Bars Meandering Stream Time Lapse Formation of an Oxbow Lake Sylvester et al., 2021 LiDAR Imagery Flood Deposition Alluvial Terraces • • • • Decrease in sediment supply Similar water supply Channel scour Excavation Stream Gradation • More sediment input = steeper stream bed • Steeper stream bed = higher water velocity • Higher velocity = lower stream bed • Sediment transport tends toward equilibrium • A graded stream is in equilibrium Graded Stream – Longitudinal Profile Evolution of a Graded Stream • Waterfalls and Rapids • Capacity exceeds load • Channel gradient reduced • Flood plain development Nick Points Waterfalls • Waterfalls and rapids – upstream erosion zone • Formation occurs on faults and resistant strata Geographic Cycle Toward graded stream Peneplain at Base Level Uplift rejuvenation Complexity = Reality • Bedrock resistance varies • Stability is rare • Crustal unloading brings isostatic compensation • Tectonic processes more consistent than sudden Fluvial Processes in Arid Climates • Deep water table • Streams loose water • Evaporation • Infiltration Fluvial Processes in Arid Climates • Short braided streams • Alluvial deposits and fans