Hydrology 101

1. Hydrology 101 OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Hydrology 101 Jason R. Vogel, Ph.D., P.E. Biosystems and Agricultural Engineering Oklahoma State University

2. Where is the water?

3. Where is the surface water in Oklahoma?

4. OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department The Hydrologic Cycle • Precipitation – rain and snow • Runoff – over the land • Stream Flow –rivers and lakes (discharge) • Lake Storage • Infiltration – into the soil • Percolation – to groundwater (recharge) • Evaporation and Evapotranspiration Source: Chow, Maidment, and Mays, Applied Hydrology, 1988

5. A Watershed is all the land that drains to one point on the landscape. P is precipitation If rain falls inside the watershed boundary, it flows toward thewatershed outlet.

6. We measure rainfall in inches of depth. Depth x area = Volume 1 inch x 1 acre = 1 ac-inch or 27,000 gallons 1 footx 1 acre = 1 ac-ft or 326,000 gallons Acres inches

7. Precipitation in Oklahoma in 2008 12.5 inches 62 inches

8. Evapotranspiration (ET) is evaporation plus transpiration Evapotranspiration ET is water that goes back to the atmosphere.

9. Introduction to Hydrology OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Evaporation/Evapotranspiration • Evapotranspiration – • Evaporation from rivers, lakes, bare soil, and vegetative surfaces • Evapotranspiration pumps water out of the ground through plant roots and leaves. • The largest part of thehydrologic cycle (globallyabout 62% of rainfallreturns directly to the atmosphere).

10. Introduction to Hydrology OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Potential ET and Actual ET • Lake Evaporation – close to Potential ET • Potential ET (PET) – ET for a well-watered reference crop (turf grass or alfalfa) • PET depends on the evaporative demand of the atmosphere • air temperature, relative humidity, solar radiation, wind speed • PET always exceeds Actual ET

11. Introduction to Hydrology OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Actual ET • Actual ET depends on how much water there is and what plants are involved.

12. Annual Average PET

13. OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Surface Water and Watersheds A Watershed is all the land that drains to one point on the landscape. Watershed Divide or Boundary Watershed Outlet

14. Runoff and Stream Flow (Q) Runoff and Stream Flow Discharge, Q, is measured in cubic feet/second (cfs)

15. OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Surface Water • How do we describe surface water? • Lakes/Reservoirs: • Stage (depth) • Volume (ac-ft or gallons) • Rivers/Streams: • Stage (depth) • Discharge, Q (cfs) • Velocity (ft/sec) Honey Creek near Grove, OK

16. http://waterdata.usgs.gov/nwis OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Hydrograph – stream stage (ft) 11.0 ft of Stage 4.0 ft of Stage

17. http://waterdata.usgs.gov/nwis Hydrograph – Discharge (cfs) 10,000 cfs 1,000 cfs

18. http://waterdata.usgs.gov/nwis OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Hydrograph and Rainfall 4 inch Rain

19. Infiltration is movement of water from surface into the soil • Depends on soil texture - Conductivity • Depends on vegetation and surface conditions • Soil Cover • Root density • Surface roughness • Depends on soil wetness • Depends onCompaction

20. OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Infiltration • Soil Texture and Hydraulic Conductivity, K:

21. OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Estimating Runoff - What doesn’t infiltrate must runoff Infiltration capacity Q Rainfall Rate Infiltration capacity declines as soil gets wetter

22. OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Runoff • Amount of runoff depends on land cover • Can be quantified through runoff coefficient…

23. OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Hydrographs Peak runoff rate Surface Runoffnoff Source: Mays, Water Resources Engineering, 2001

24. OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Hydrographs The water table supplies baseflow to the stream. Source: Mays, Water Resources Engineering, 2001

25. OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Hydrographs

26. OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Shape of the hydrograph also depends on… • Temporal distribution of rainfall • Impervious areas of the watershed • Ponds, diversions, and flood control structures Source: Mays, Water Resources Engineering, 2001

27. OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Shape of the hydrograph depends on construction, compaction, and impervious area. Impervious Area After construction Before Source: Mays, Water Resources Engineering, 2001

28. Loads and Concentrations • Concentration is measured as parts per million or mg/L. • Load is the quantity of material per unit time – it is measured in Pounds/Day, Tons/Year, Kilograms/hour, grams/second. • To measure load, you need both a concentration and flow rate: Load = Concentration x Discharge

29. OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Hydrologists use Statistics… • Hydrologic statistics  Frequency Analysis • Magnitude of Storms, Floods, or even Drought can be described by its frequency. • Bigger events occur less frequently. • We can describe the size event by its expected frequency or Return Period.

30. OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Return Period • Return Period (T) = average recurrence interval between events equaling or exceeding a specific magnitude

31. Return Period – another way to look at it The probability of an event is the inverse of its return period. • A10-yr storm has 1/10 or 10% chance of occurring in any given year. • A 100-yr storm has 1% chance. Note: a 500-yr storm is bigger than a 100-yr storm, but it may not be much bigger. …and return period is estimated from the period of record – but we do not know the future.

32. Hydrologic Considerations for Water Quality • Everything in the watershed affects water quality, but not everything is equally effective. • Most pollutants travel with water – how much water determines when and how much the pollutants arrive. • Some water infiltrates the soil – and takes pollutants with it. • Some pollutants break down or become stabilized before they reach the water body. • Some pollutants originate near or in the stream (these are the first concern).

33. Hydrologic Considerations for Water Quality • Nonpoint pollution is dependent on rainfall frequency (probability) • Does not occur every day • Magnitude of rainfall varies • Consider the return period or probability of occurrence • Impervious areas transmit pollutants more effectively than areas where infiltration occurs. • Roads make very efficient channels –carry water and pollutants.