oklahoma state university biosystems and agricultural engineering department hydrology 101 oklahoma...

OKLAHOMA STATE UNIVERSITYBiosystems and Agricultural Engineering Department

Hydrology 101

Hydrology 101


Hydrology 101

Jason R. Vogel, Ph.D., P.E.

Biosystems and Agricultural Engineering

Oklahoma State University


Hydrology 101

Where is the water?

Oceans and Saline Ground Water

97%

Polar Ice69%

Ground Water30%

Just 0.01% is in All Rivers, Lakes, and Wetlands


Hydrology 101

Where is the surface water in Oklahoma?


Hydrology 101

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 ground

water (recharge) Evaporation and

Evapotranspiration


Source: Chow, Maidment, and Mays, Applied Hydrology, 1988


Hydrology 101

A Watershed is all the land that drains to one point on the landscape.

If rain falls inside the watershed boundary, it flows toward thewatershed outlet.

P is precipitation


Hydrology 101

We measure rainfall in inches of depth.

Depth x area = Volume1 inch x 1 acre = 1 ac-inch or 27,000 gallons

1 foot x 1 acre = 1 ac-ft or 326,000 gallons

Acres

inches


Hydrology 101

Precipitation in Oklahoma in 2008

62 inches

12.5 inches


Hydrology 101

Evapotranspiration (ET) is evaporation plus transpiration

ET is water that goes back to the atmosphere.

Evapotranspiration


Hydrology 101

• 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).


Introduction to Hydrology

Evaporation/Evapotranspiration


Hydrology 101

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




Hydrology 101

Actual ET• Actual ET depends on how much water

there is and what plants are involved.




Hydrology 101

Annual Average PET


Hydrology 101

Surface Water and Watersheds

A Watershed is all the land that drains to one point on the landscape.


Watershed Divide or Boundary

Watershed Outlet


Hydrology 101

Runoff and Stream Flow (Q)

Runoff and Stream Flow

Discharge, Q, is measured in cubic feet/second (cfs)


Hydrology 101

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


Hydrology 101OKLAHOMA STATE UNIVERSITYBiosystems and Agricultural Engineering Department

Hydrograph – stream stage (ft)

11.0 ft of Stage

4.0 ft of Stage

http://waterdata.usgs.gov/nwis



Hydrology 101

Hydrograph – Discharge (cfs)

10,000 cfs

1,000 cfs





Hydrograph and Rainfall


4 inch Rain



Hydrology 101

• Depends on soil texture - Conductivity• Depends on vegetation and surface

conditions– Soil Cover – Root density– Surface

roughness• Depends on

soil wetness• Depends on

Compaction

Infiltration is movement of water from surface into the soil


Hydrology 101

Infiltration


– Soil Texture and Hydraulic Conductivity, K:

Soil Texture Typical K (inches/hr)

Sand 4.64

Loamy Sand 1.18

Loam 0.13

Silt Loam 0.26

Sandy Clay 0.024

Clay 0.012


Hydrology 101

Estimating Runoff - What doesn’t infiltrate must runoff


Q

Infiltration capacity declines as soil gets wetter

Infiltration capacity

Rai

nfal

l Rat

e


Hydrology 101

– Amount of runoff depends on land cover• Can be quantified through runoff coefficient…

Runoff


Description Runoff Coefficient

Pavement:Asphalt, Concrete 0.70-0.95

Lawns, sand soil:2% (Flat)>7% (Steep)

0.05-0.100.15-0.20

Residential:Single FamilyApartments

0.30-0.500.50-0.70


Hydrology 101

Hydrographs


Source: Mays, Water Resources Engineering, 2001

Peak runoff rate

Surface Runoffnoff


Hydrology 101

Hydrographs



The water table supplies baseflow to the stream.



Hydrographs


Hydrology 101

Shape of the hydrograph also depends on…


• Temporal distribution of rainfall• Impervious areas of the watershed• Ponds, diversions, and flood control structures



Hydrology 101

Shape of the hydrograph depends on construction, compaction, and impervious area.



Before

Impervious Area After construction


Hydrology 101

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


Hydrology 101

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.



Hydrology 101

Return Period– Return Period (T) = average recurrence interval between

events equaling or exceeding a specific magnitude


yearsyrsT

yrsyrsyrsyrsyryryrs

57

35

3556315114

20062001199519921977197619751971


Hydrology 101

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.


Hydrology 101

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).


Hydrology 101

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.

oklahoma state university biosystems and agricultural engineering department hydrology 101 oklahoma...

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