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Hydrologic Overview & Quantities

Hydrologic Overview & Quantities. It is important to understand the big picture when attempting to forecast. This includes the interactive components and hydrologic quantities. Hydrologic Cycle. Precipitation. Evapotranspiration. Interception. Storage. Infiltration. Runoff. Streamflow.

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Hydrologic Overview & Quantities

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  1. Hydrologic Overview & Quantities It is important to understand the big picture when attempting to forecast. This includes the interactive components and hydrologic quantities.

  2. Hydrologic Cycle Precipitation Evapotranspiration Interception Storage Infiltration Runoff Streamflow

  3. Energy Sphere Atmosphere Hydrosphere Biosphere Terrasphere The complexity of what we are trying to accomplish…. Evaporation & Condensation The Water Budget Antecedent Moisture Conditions Photosynthesis & Respiration Infiltration Variable Source Area Transpiration & Interception Time of Concentration The “sphere” concept was borrowed from Dr. Peter Black:Watershed Hydrology – 2nd Edition, Peter Black, 1996, Ann Arbor Press (ISBN# 1-5704 027-1)

  4. Models try to mimic this! Infiltration Excess Precip. Interception Storage Basin Process Representation Time Series Time Series

  5. From A Basin View Excess Precip. Excess Precip. Model Basin “Routing” Runoff Hydrograph Stream “Routing”

  6. The Runoff Picture • Hydrology is long term and short term…. • In this course we will mainly focus on the short term: • Floods & flood flows. • Generating runoff/high flows. • Predicting/forecasting flows. • Space/time scales.

  7. Recipe(s) for a Flood/High Flows • What causes a flood / high flow? • What are the conditions? • What are the types of flooding situations? • Your area or other areas…..

  8. What Are the Defining Characteristics of a Flood? • Timing – rise time, recession, duration. • Flows – peak flows, magnitude (statistical). • Precipitation – intensity, duration, frequency….

  9. What Controls the Timing, Flow, and Precipitation? • The hydrology – short term and long term. • The meteorology – short term (weather/storm type) and long term (climate).

  10. Short TermWeather (storm type) & “current hydrologic conditions”

  11. Watershed Characteristics • Area • Slope • Land Use • Soils • Geology • Climate • Geomorphology

  12. Some of the “Right” Combinations…. • Precipitation –vs.- infiltration • Precipitation intensity > infiltration rate • Precipitation total > infiltration capacity • “Storage” in the system is full • Human induced high water or flows • Natural alterations to the watershed

  13. Our Focus - Forecasting • Must be both short & long term.. • The combination(s) of precipitation and hydrologic conditions that lead create a potential flooding situation… • “basin hydrology” – basin hydrology looks at the hydrologic budget in both the short and long term.

  14. How much water is there?Distribution of Earth's Waters and Residence Times....

  15. Units & Properties of Water

  16. Area Some Common Unit Conversions • 1 acre = 43,560 ft2 • 1 mi2 = 640 acres • 1 hectare = 100m x 100m = 2.471 acres = 10,000 m2 • 1 km2 = 0.386 mi2

  17. Volume • 1 acre-foot = 1 ac-ft = 1 acre of water x 1 foot deep = 43,560 x 1 = 43,560 ft3 • 1 ac-inch = 1 acre x 1 inch deep = 43,560 x 1/12 = 3,630 ft3 • 1 ft3 = 7.48 gallons • 1 gallon H2O ~ 8.34 lbs.

  18. Runoff Volume • 1-inch of runoff over 1 square mile : • 1/12 feet x 1 mi2 x 640 acres/mi2 x 43,560 ft2/mi2 = 2,323,200 ft3

  19. Discharge • 1 cfs = 1 cubic foot per second • 1 cfs x 7.48 gal/ft3 x 3600 sec/hr x 24 hrs/day = 646,272 gpd = 0.646 MGD • 1 cfs x 3600 sec/hr x 24 hrs/day = 86,400 cfs/day • 86,400 cfs/day x 1 ac-ft/43,560 ft3 = 1.983 ac-ft/day (~ 2 ac-ft/day) • 1.983 ac-ft/day x 12 inches/ft x 1 day/24 hrs = 0.992 ac-in/hr • 1 ac-in/hr x 43,560 ft3/ac-ft x 1 hr/3600 sec x 1 ft/12 inches = 1.008 cfs

  20. Power • Hp = gHQ/550 • 1 hp = 550 ft*lb/sec = 0.7547 kilowatts g = weight of water H = head or elevation difference Q = flow Hydropower wants a lot of flow and a full reservoir…..

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