Hydrology Exam 3.txt

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TipTheScales
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214015
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Hydrology Exam 3.txt
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2013-04-17 00:42:13
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Hydrology
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Hydrology Exam 3
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  1. Infiltration:
    The flow of water from the ground surface into the soil
  2. Groundwater zone:
    Also called the saturated zone, where water completely fills up the pore spaces
  3. The water table:
    The top of the saturated/groundwater zone
  4. Soil water:
    Occurring in the unsaturated zone, where some pores contain water and others, air
  5. Unsaturated zone:
    Where soil is only partially infiltrated with water
  6. How does water travel in the saturated zone?
    Motion along the path of decreasing gravitational potential energy
  7. What factors affect infiltration rates?
    • Water viscosity (the greater, the lesser the infiltration)
    • Soil permeability (the greater, the greater the infiltration)
  8. What affects water viscosity?
    Increases with decrease in temperature
  9. What affects soil permeability?
    • Soil type: Fine-grained vs. coarse-grained
    • Rainfall intensity: The heavier the rain, the lesser the rate of infiltration (due to the compactment of the soil increasing water being run off
    • Water quality: Calcium ions in water makes clay flocculate (the combination of clay particles to form crumbs), increasing permeability, whereas sodium ions cause deflocculation
  10. How to measure infiltration?
    • It would be inaccurate, but our best estimate would be to determine the average depth of rainfall over a drainage basin and subtract from that the measurement of streamflow out of the basin (runoff; this method does ignore evaporation)
    • Another way is to map all the soil types in the basin and make infiltrometer measurements on each soil type, similar to the Theissen method of finding total precipitation over a basin.
  11. Soil water:
    Subsurface water in the unsaturated zone
  12. Porosity (Soil Water; what it is and what it depends on):
    • Volume of pore spaces/total volume
    • Depends on grain shape, arrangement, and degree of assortment
    • (Size not that important)
  13. Field capacity (Soil Water):
    Volume of capillary water/total volume; quantity of water held against gravity
  14. Gravity water:
    Pore volume-capillary water
  15. Specific yield (Soil Water):
    • Volume of gravity water/total volume; after the saturation point
    • (Higher with higher permeability)
  16. How to measure soil in water:
    • Gravimetric method: Weigh, dry, reweigh (disadvantage is the removal of study soil)
    • Tensiometer: measures capillary “suction” force of soil pores (H2O from tube with porous staff is sucked out as soil dries, creating a measurable vacuum; the relationship between the soil water tension and the particular soil can approximate the soil water content; may be expensive, hoever)
  17. Irrigation methods:
    Gravity (Furrows, Wild Floods), Sprinklers, Drip Irrigation
  18. Gravity Irrigation:
    • Furrows: For “row” crops, from higher to lower elevation
    • (Challenges: adequate steepness, erosion, evaporation, infiltration {bad water quality})
    • 
Wild Floods: Surrounding land with embankments to form basin and then flooding it with water
    • (Challenges: Uniform distribution, erosion, evaporation, infiltration…30-50% efficiency)
  19. Sprinklers:
    • Used when there is groundwater or soil permeability is too high
    • Less water used, higher efficiency, , low risk of erosion/infiltration, but higher energy need
  20. Drip Irrigation:
    • Direct to root irrigation
    • Highest efficiency, but high cost, chance of clogging, possible salt deposits
  21. Most irrigated states:
    • (dry west (of 100th meridian), humid east)
    • California, Nebraska, Texas, Arkansas, Colorado. Kansas, Idaho, Florida, Washington, Oregon
  22. Comparison of irrigation between states:
    • Irrigation techniques depend of the type of crop and the water source.
    • To compare, the west uses =< 20 in. rain/year (generally melted snow)…our gw is >100 ft deep, expensive to pump; East uses ~30 in. rain/year (generally gw)
  23. How much of the population uses groundwater?
    50%
  24. Groundwater comprises how much of our freshwater supply?
    25%
  25. Zone of saturation:
    Groundwater reservoir
  26. Aquifer:
    A geologic formation that is both porous and permeable, storing, trasmiting and yielding significant amounts of water
  27. What makes a good aquifer?
    High porosity, high permeability
  28. Best aquifers?
    Unconsolidated sand/gravel, coarse-grained
  29. Consolidated Sediments serving as aquifers
    • Volcanic rock
    • Sandstone
    • Limestone
    • Fractured grantie
  30. Unconfined aquifer:
    Unconfined beneath the water table (watertable aquifers
  31. Confined aquifer:
    Confined underneath an impermeable boundary
  32. Perched aquifer:
    Groundwater body perched on an impervious formation above the regional water table
  33. Porosity (Ground Water):
    • Ratio of space available to water to volume of aquifer
    • Primary: upon first formation of aquifer
    • Secondary: after cracking or dissolution has occurred
  34. Permeability:
    • A porous mediums ability to transmit fluid
    • Determined by size and degree of interconnected ness between pore spaces
  35. Darcy’s law
    • Q = K A ((h1-h2)/L)
    • Where Q = quantity of discharge (Volume/Time)K = coefficient of
    • permeability = hydraulic conductivity (property of fluid + material;
    • distance/time)Q/A=KiI= (h1-h2)/ L =hydraulic gradient
    • Real velocity = Vx =V/n where n=porosity
    • V= Ki Apparent Velocity
  36. Specific retention:
    • Volume of capillary water/total volume;
    • Capillary water held after a particular drainage time

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