K. Chapter 12 - Chapter 12 Running Water Def'n: Hydrosphere...

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Chapter 12 Running Water Def’n: Hydrosphere – consists of the waters on the Earth including water vapor in the atmosphere,groundwater (studied in Chapter 13), water in the oceans, running water on the continents, and frozen water in glaciers (Chapter 14). The hydrosphere interacts with the Earth’s other systems. See Table 1.1, p. 8. Def”n: Hydrologic Cycle – The continuous recycling of water from the oceans, through the atmosphere, to the continents and back to the oceans. See Figure 12.4, p. 337 This cycle is: 1.) powered by solar radiation 2.) possible because water easily changes state (from liquid to gas) under surface conditions. The running water portion of the hydrosphere is very important in sediment erosion, transportation, and deposition, and is therefore the most important geologic process modifying Earth’s land surface. In order to understand the hydrosphere, we need to look at the hydrologic cycle. This is a dynamic, continuous cycle just as the rock cycle is a dynamic, continuous process of change from one rock type to another. Running Water Characteristics of Flow Laminar – streamlines are parallel to one another Little or no mixing between adjacent layers Ex.) viscous fluids such as cold motor oil or syrup Turbulent – streamlines are complexly intertwined Mixing between adjacent layers in the fluid Ex.) water is low viscosity, so turbulent Controls on water’s viscosity: - temperature - velocity - roughness of the surface over which flow occurs Turbulent flow is energetic, capable of erosion and sediment transport. This chapter deals with turbulent water flow.
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During a rainstorm, water collects on a surface and moves downslope. This is runoff. Depends on: Def’n: Infiltration capacity – the rate at which surface materials can absorb water. Controlled by: Intensity and duration of rainfall Condition of surface (wet or dry; loosely unconsolidated or packed) Water flow is initially slow and causes little erosion. As water moves downhill, it accelerates. Sheet flow – a more or less continuous sheet of shallow water moves over the surface. May cause sheet erosion. Channel flow - confined to long trough-like depressions that vary from tiny rills to huge rivers. We will use the terms stream and river when discussing channel flow. Characteristics of Channel Flow Gradient vertical drop _____ horizontal distance Ex.: a river’s source is 1000 m above sea level and it flows a distance of 500 km. 1000 m --------- = 2 m/km gradient 500 km Gradient varies : between channels along a single channel. Rivers and streams are typically steeper near their headwaters than where they discharge into the sea. Velocity – the downstream distance water travels in a given time. Usually m/sec or ft/sec Flow velocity varies across a channel’s width as well as along its length. Velocity is slower and turbulence is greater near a channel’s bed and banks due to increased friction. Velocity is also influenced by channel shape and roughness.
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This note was uploaded on 04/16/2008 for the course GEOL 1403 taught by Professor Teague during the Spring '08 term at Tarrant County.

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K. Chapter 12 - Chapter 12 Running Water Def'n: Hydrosphere...

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