# What is the water (hydrologic) cycle? Why is it important?

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What is the water (hydrologic) cycle? Why is it important?

The hydrologic cycle http://observe.arc.nasa.gov/nasa/earth/hydrocycle/hydro2.html

The Hydrologic Cycle F Water input and output is in balance (globally) P = R + ET

The Hydrologic Cycle F Local variations can have serious consequences (floods or drought) F http://observe.arc.nasa.gov/nasa/exhibit s/flood/flood_1.html http://observe.arc.nasa.gov/nasa/exhibit s/flood/flood_1.html http://observe.arc.nasa.gov/nasa/exhibit s/flood/flood_1.html F http://ma.water.usgs.gov/floods/flood_2 006_05.html http://ma.water.usgs.gov/floods/flood_2 006_05.html http://ma.water.usgs.gov/floods/flood_2 006_05.html

Hydrologic Balance F Measuring the amount of water coming in and going out to assess availability

Measuring Runoff (R) F Measure how fast the water is moving in the stream (velocity, ft./sec) width depth velocity F F velocity (ft/sec) x area (sq. ft) = cu.ft/sec F Measure the width and depth of the stream = area (sq. ft.) stream = area (sq. ft.)

Precipitation (Input) F How do we measure it? F Rain gauge collects 1 inch of rain. What does that mean? F In a one-inch rain, what is the volume of water that falls on an area of one square mile?

Measuring Precipitation (P) F 1 inch = 1/12 feet F 1 sq. mi = 5,280 ft x 5,280 ft = 27,878,400sq.ft. F 27,878,400 sq.ft. x 1/12 feet = 2,323,200 cu.ft. F 2,323,200 cu.ft. x 7.48 gal./cu.ft = 17,377,536 gals. (17 x 10 6 gals.) F If rain fell over 1 day, the rate is 2,323,200 cu. ft. ÷ 86,400 sec/day = 26.9 cu. ft/sec.

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