Aquifer geometry and groundwater flow geology and

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Aquifer Geometry and Groundwater Flow Geology and geometry of rocks and sediments will control the behavior of ground water An aquifer without an aquitard above it is an unconfined aquifer An aquifer with an aquitard above and below is a confined aquifer A confined aquifer may see hydrostatic water pressure increase and form an artesian system Drilling into a confined aquifer under pressure will see the water rise above the aquifer In this system the potentiometric surface is the height to which the water would rise
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Aquifer Geometry and Groundwater Flow
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Groundwater Flow Hydraulic head is potential energy in an aquifer – The height of water in an unconfined aquifer reflects the hydraulic head • The higher the water table the higher the head – Ground water flows spontaneously from areas of high hydraulic head to areas with low hydraulic head – Flow velocity is a product of hydraulic conductivity and hydraulic head (Darcy’s Law)
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Soluble rocks and karst
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Dissolution in the subsurface may lead to sinkholes
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Another storage: lakes (~100,000 km3 globally)
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Origin of lake basins: 1. Glacial (Great Lakes) 2. Tectonic (Lake Tahoe, Lake Baikal) 3. Volcanic (Crater Lake, OR) 4. Karst lakes (sinkholes filled with water) 5. River erosion (oxbow lakes) 6. Landslides blocking river valleys
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Streams and Rivers Stream , a flowing water within a channel Drainage basin , a region from which a stream draws water Discharge , the volume of water flowing past a given point/cross section in a specified length of time Load , the total quantity of material that a stream transports by all methods (traction, saltation, suspended, and dissolved) Capacity , a measure of the total load of material a stream can move Gradient , the steepness of the stream channel Base level , the lowest elevation to which the stream can erode downward
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Drainage Basin – Watershed
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Anatomy of a river valley
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Drainage Basin – Watershed
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River Discharge (flow velocity x cross sectional area)
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River Load
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Velocity and Sediment Sorting and Deposition Stream velocity impacts sediment sorting Slow moving water only carries fine-grained sediments Swift moving water carries a wider range of grain sizes Sediments are commonly sorted by size and density Depositional features of a stream Delta , a large, fan-shaped pile of sediment in still waters created by a stream Alluvial fan , a fan-shaped pile of sediment in a larger stream or a region between mountains and a plain formed by a small tributary stream
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Sediments accumulate where water slows down
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Lowland River (meandering) no or little vertical incision lateral erosion channel slope is gentle
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Channel and Floodplain Evolution Meanders , streams don’t flow in straight lines and erode old banks and create new banks, and thus bends form in the streams. Meanders are curves in a stream (or river) Cut bank , the outside and downstream side of the meander.
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