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Where is most of the freshwater contained on the planet
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98% of all freshwater is contained in the antartic ice sheet. Approximately 1.2% of the left over freshwater is contained in the greenland ice sheet.
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Drainage basin
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The land areas that contribute to flow of a particular stream at a particular point.
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Rain making mechanisms
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-Orographic (Mountain precipitation)
-Air Instability (thunderstorms) |
What is going to determine what kind of events are going to occur in a drainage basin?
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Scale of a drainage basin.
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Problems with rain gauges
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-Usually at airports have have no trees and therefor nothing to intercept the falling precipitation.
-Gauges tend to move around cities as the city grows so it gives inconsistant data or double mass curves. |
Converting point data to spatially average data
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1. Arithmatic mean
2. Theissan Polygons 3. Isohyetal method |
Arithmatic Mean
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Good for quick measurements. Not accurate, as all places will end up with the same amounts.
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Theissan Polygons
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Irregular polygons drawn around each rain gauge where you can measure the effect of rain on each gauge.
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Isohyetal Method
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Using lines of equal rainfall. Allows to interpolate the pattern of rainfall in the way that it actually fell. Topography affects rainfall amounts and this method will reflect that.
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Frequency analysis
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Concept of the size of the event is bound up in its frequency.
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Return period is calculated by:
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Return period = 1/Probability
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Evaporation Pans (problems)
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The conditions of heat exchange and air flow around an evaporation pan differ from those of thw water body they are intended to reflect.
Therefor, data from the pans must be adjusted by a correlation factor called a pan coefficient. |
Most common type of evaporation pan
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Class A evaporation pan.
-Circular pan of ungalvanized iron. -4 ft in diameter -10 inches deep. -Supported on frame 6 inch off ground. |
Methods of measuring or calculation evaporation
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1) Evaporation Pans
2)Mass transfer equations 3) Water budgeting |
Hydrologic Data
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Most hydrologic data is expressed in units of depth (cm, mm) volume (m3), or rate (Depth of volume)
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