1 / 191

COMET University Faculty Hydrometeorology Course June 2000

COMET University Faculty Hydrometeorology Course June 2000. Dennis L. Johnson. Dennis L. Johnson, Asst. Professor Juniata College Environmental Science & Studies (814) 641-5335 (Phone) (814) 641 – 3685 (Fax) Johnson@juniata.edu (Email) Http://www.Juniata.edu/~johnson/. Usual Houghton.

lilike
Download Presentation

COMET University Faculty Hydrometeorology Course June 2000

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. COMET University FacultyHydrometeorology CourseJune 2000 Dennis L. Johnson

  2. Dennis L. Johnson, Asst. ProfessorJuniata CollegeEnvironmental Science & Studies(814) 641-5335 (Phone)(814) 641 – 3685 (Fax)Johnson@juniata.edu (Email)Http://www.Juniata.edu/~johnson/

  3. Usual Houghton

  4. Hydrometeorological Operations in the “Modernized NWS”

  5. 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.

  6. What’s a Flood? • What is a flood????? • A rather elusive definition • Generally contains terms like: • High water • High flows • Normal water course • Human impact(s) • Etc…

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

  8. My Recipes • “BIG” heavy soaking rains… • Low infiltration rates • Snow melt • Rain on snow • Very intense precipitation • Dam failure • Others….??

  9. Does a Flood Have to Happen in a Defined Water Course or Waterway? ….and If a Flood Does Occur in an Overland Situation – Does the Nearest Stream Even Feel It?

  10. FEMA - NFIP…(www.fema.gov/nfip) Flood--A general and temporary condition of partial or complete inundation of normally dry land areas from: Overflow of inland or tidal waters. The unusual and rapid accumulation or runoff of surface waters from any source. Mudslides (i.e., mudflows) which are proximately caused by flood, as defined above, and are akin to a river of liquid and flowing mud on the surface of normally dry land areas, as when earth is carried by a current of water and deposited along the path of the current. The collapse or subsidence of land along the shore of a lake or other body of water as a result of erosion or undermining caused by waves or currents of water exceeding the cyclical levels which result in flood, as defined above.

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

  12. 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).

  13. Big Picture Long term and short term

  14. Long Term(Climate and the Hydrologic Cycle)

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

  16. 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

  17. Our Focus • More on the short term.. • The combination(s) of precipitation and hydrologic conditions that lead up to a potential flooding situation… • “basin hydrology” – although basin hydrology looks at the long term hydrologic budget, as well.

  18. Let’s Take a Minute to Look at Hydrology and the Properties, Units, Concepts, & Terminology

  19. Hydrology … An Earth Science. It Encompasses the Occurrence, Distribution, Movement, and Properties of the Waters of the Earth and Their Environmental Relationships." (Viessman, Knapp, Lewis, & Harbaugh, 1977 - Introduction to Hydrology, Harper & Row Publishers, New York)

  20. History of Hydrology (Hydrometeorology)

  21. Early on…. • Early philosophers speculated on the hydrologic cycle: • Homer believed that there existed large subterranean reservoirs that fed the rivers, seas, springs, and wells - was he wrong? • Homer did understand the dependence of flow in the Greek aqueducts on conveyance and velocity!

  22. History, Cont.... • In the first century B.C., Marcus Vitruvius in the treatise de Architectura Libri Decem (the engineers chief handbook), vol. 8 hypothesized that rain and snow falling in the mountains infiltrated into the earth’s surface and appeared in the lowlands as springs and streams.....

  23. Early Success..... • 4000 b.C. The Egyptians built a dam on the Nile to allow barren lands to again be used for agricultural purposes.

  24. More Early Successes • 1000’s of years later, a canal to carry fresh water from Cairo to Suez was built. • Towns in Mesopotamia were protected by flooding from high earthen walls.

  25. Early Disputes and Rules • The cities of Lagash and Umma of Mesopotamia have documented water disputes. • The Romans decree: • Ne quis aquam oletato dolo malo ubi publice saliet si quis oletarit sestertiorum X mila multa esto. • It is forbidden to pollute the public water supply; Any deliberate offender shall be punished by a fine of 10,000 sesterces!

  26. Qualitative Understanding • Near end of 15th century, Leonardo da Vinci and Bernard Palissy independently reached conclusions on the hydrologic cycle - based on a philosophical understanding. • There was still a lack of quantitative understanding of the hydrologic cycle.

  27. The 17th Century • Perrault, Mariotte, and Halley began quantitative measurements and applications. • Perrault measured rainfall and runoff over the seine river drainage basin for ~ 3 years - he illustrated that rainfall WAS adequate in quantity to account for river flows. • Mariotte gauged the velocity of the flow in the river seine and estimated flows by also estimating river cross sectional areas. • Halley was an astronomer! He estimated evaporation from the Mediterranean sea and correlated it to river flows into the med, concluding that river flows were sufficient enough to provide that volume of water.

  28. The 18th Century • Bernoulli - famous for hydraulics and fluid mechanics - the piezometer, the pitot tube, and Bernoulli’s theorem. • The Chezy formula (channel flow).

  29. The 19th Century • Hagen-Poiseuille - capillary flow equation. • Darcy’s - flow in porous media. • Duptuit-Thien well formula. • Manning - open channel flow. • Systematic stream gaging. • Mostly empirical in nature.

  30. The 20th Century • Government agencies began to develop programs – good or bad? • Rational analysis begins. • Sherman - unit hydrograph theory. • Horton - infiltration theory. • Snyder - unit hydrograph. • Clark - unit hydrograph. • Etc...........

  31. Modern Day • Very computer and data intensive • High tech instruments • Scale issues • Policy issues • Etc................. • “Diamond edge on an old axe”……

  32. Units & Properties of Water

  33. The Watershed • A watershed is an area of land that drains to a single outlet and is separated from other watersheds by a divide. • Every watershed has a drainage area. • Related terms: drainage basin, sub-basin, sub-area.

  34. Area • 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

  35. 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.

  36. 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

  37. 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

  38. Power • Hp = gHQ/550 • 1 hp = 550 ft*lb/sec = 0.7547 kilowatts

  39. Hydrology Terminology • Streamflowis the movement of water through a channel. • Thecross-sectional areaof a stream is the region bounded by the walls of the stream and the water surface. The cross-sectional area is illustrated below. • See alsoManning’s “n”. Cross-sectional Area Stream Flow

  40. Diagram 1 Diagram 2 Hydrology Terminology • Manning’s “n”is a measure of the roughness of a surface, and in streamflow it is the roughness of the channel bottom and it’s sides. Diagram 2 will have a higher Manning’s “n” because it has rougher surface due to the jagged bottom and pebbles.

  41. Routing Hydrologic Hydraulic Hydrology Terminology • Routing is used to account for storage and translation effects.

  42. Hydrology Terminology Generalized effect of routing

  43. Hydrology Terminology • Snowfallis a form of precipitation that comes down in white or translucent ice crystals. • Snowmeltis the excess water produced by the melting of snow. This leads to flooding possibilities in the spring when temperatures begin to rise. There is generally a delay in the snowmelt response of a basin due to the melting process and travel times. • Snowpackis the amount of annual accumulation at higher elevations.

  44. Hydrology Terminology • Runoffis the excess precipitation and is often considered a “fast” response. • Overland flowis the flow of water across the land surface. • Sub-surface flowis the flow of water through the soil layers to the stream. • Baseflowis the flow in a channel due to ground water or subsurface supplies. The baseflow is generally increased by precipitation events that produce enough infiltration.

  45. Hydrology Terminology • Infiltrationis the movement of water from the surface into the soil. • The rate of infiltration is based on a number of factors, including but not limited to: • soil types • current conditions • precipitation intensity

  46. Hydrology Terminology • The velocity of the flow is very dependent on the slope of the stream bottom. The greater the slope the greater the potential velocity of the flow. • The “wave” speed is the velocity of the flood wave down the channel. The speed of this wave affects how quickly the downstream area will effected.

  47. Energy Grade Line headloss Hydraulic Grade Line (water surface) Depth1 Channel Bottom Elevation Head Depth2 Datum Hydrology Terminology • Theenergy grade linerepresents the depth of the water surface and the velocity component of the Bernoulli equation. • Thehydraulic grade linerepresents the depth of the water surface.

  48. Hydrology Terminology • Karst hydrology is caused by pores and holes in limestone formations. This increases the infiltration into the limestone, reducing the runoff potential. • The slope changes the speed of runoff and therefore effects collection times.

  49. Hydrology Terminology • The frequency of a storm event is described by its return period. For example a two year storm event has a 1 in 2 chance of occurring in any given year. • The probability is also affected by the return period. Thus the probability of a 2 year storm occurring is 50%. The probability of a 100-year event occurring is 1/100 or 1%

  50. Basin Hydrology

More Related