Lecture 25 running water

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Today: Chapter 15: Running Water Announcements: Please not call Aurora on her cell phone number If you need to make contact, so by email Thanks! Homework assignment: Review Interlude E: The hydrological cycle and complete assignment Will be handed out on Monday at the beginning of class and will be due on Wednesday Quiz next Wednesday covering: - Interlude D: Fossils and Evolution - Chapter 12: Deep Time (Historical Geology) - Chapter 16: Mass wasting - Chapter 17: Running water oceans dams plants s r e ir v evaporation lakes rain sediments & soil mountains snow To think about for Monday’s homework: The hydrological cycle Describe how these 10 elements are interrelated in the hydrological cycle Chapter 15: Running Water Topics for today: Hydrological cycle Surface run-off Sheet wash Channel flow Discharge = Velocity x Channel Area Turbulent and laminar flow Stream transport processes Drainage basins and divides Base level and stream profiles Processes of stream erosion How streams carve their channels Processes of stream deposition Downstream changes in channel form and bahavior Effects of changing base level Running Water: Why Care? Running Water: Why care? Running Water: Why care? Hydrological Cycle & Running Water Hydrological cycle (see video): Continuous cycling of water between the atmosphere, oceans and land, driven by gravity and energy from the Sun Running water is the most effective agent of erosion and the dominant external factor in shaping the Earth’s surface Important factors that affect the ability of running water to alter the landscape:  Rainfall  Surface runoff  Rate of evaporation Earth’s Water Inventory Sources of water that sustain stream flow… Fig 17.02 W W Norton Meanders: See videos Where streams become choked with sediment, “braided channels” form This is common where there is a locally abundant supply of sediments Formation of an oxbow lake… Fig 17.26 b W W Norton Fig 17.21 d (c) Martin Miller Elevated floodplain terraces Raising the base level of a stream leads to deposition of sediments and can induce meandering… Fig 17.21 b W W Norton Lowering base level can cause vertical erosion and channel incision, with the formation of terraces… Fig 17.21 c W W Norton Channel incision and terrace formation… Did base level go up or down here? What happened to base level upstream from the dam? Incised meanders What happened to base level here? Base level can be altered by: 1) Local or regional uplift 2) Sea level change Fig 17.10 a, b W W Norton Deltas form where streams enter a lake or the ocean Fig 17.27 a Modified from Hamblin and Christiansen, 1988 As streams enter a standing body of water they lose velocity and deposit their sediment The name “delta” derives from the similarity in shape of classic deltas to the Greek letter of that name… Fig 17.27 b Modified from Hamblin and Christiansen, 1988 Not all deltas have the classic shape Where wave erosion is weak, channels may build outward into the ocean forming a “birds foot: delta, like the Mississippi Fig 17.27 c Modified from Hamblin and Christiansen, 1988 [...]... Sheet flow then accumulates and self-organizes into rivulets and small channels that eventually feed into streams Major River Systems of the Earth RUNNING WATER Stream Valleys Most common surface landform on Earth! V-shaped near headwaters, with many water falls and rapids Slotted canyons may form where bedrock is easily eroded Widen downstream due to erosion of by slope wash and gravity Fig 17.19... directions Major Drainage Basins of North America Fig 17.07 RUNNING WATER Stream Profiles Longitudinal Stream Profile: A cross sectional view that shows how the slope of a stream channel changes along its course Longitudinal stream profile Fig 17.05 a W W Norton Cross sectional profiles at different points along stream course RUNNING WATER Base Level Base level: The downward limit to which a stream.. .RUNNING WATER Process Begins with Surface Runoff “Sheet flow”: Thin sheets of water accumulate and flow over surface Controlled by:  Intensity/duration of rainfall  Soil texture  Soil saturation  Slope angle  Vegetation Initiation of stream... Streams naturally extend their channels in the direction of their headwaters by a process called “headward erosion” Plateau incision by headward erosion… Fig 17.03 d Stephen Marshak A waterfall is a temporary irregularity in the equilibrium profile of a stream that is eventually erased by erosion Fig 17.22 b Stephen Marshak Removal of a waterfall is accomplished by undercutting at the base of the fall... accomplished by undercutting at the base of the fall and collapse of the channel above… Fig 17.24 b W W Norton Rapids… Fig 17.23 Class II W W Norton Extreme Rapids… Fig 17.23 Class V W W Norton RUNNING WATER Movement of Water During Stream Flow Types of flow: Characteristics of flow: Laminar Flow paths follow straight lines, parallel to channel walls Erosive power is relatively low Mode for low stream... whirlpool-like motions Occurs at high velocity & where channel walls are rough Erosive power relatively high! Announcements: Read Chapter 22, “Glaciers”, for Friday I will wrap up the course on Monday with a lecture drawn from Chapter 23 on “Global Change” Review outline for final will be posted to the website on Monday An final update of course grades will also be posted on the course website on Monday
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