HYDROLOGY – LECTURE 1
Hydrology as a science and as a profession
Hydrologic cycle and world water balance
Water as a physical substance
Water data sharing
Engr. NLB
LECTURE OBJECTIVES
1. Understand the major components of the hydrologic
cycle.
2. Appreciate the wide variety of precipitation types in
various climate regions and lay a foundation for how
precipitation affects upcoming topics such as runoff and
erosion.
3. Quantitatively use important concepts such as return
period and storm duration.
4. Discuss precipitation data availability
Key Words: hydrology cycle, precipitation, water balance
HYDROLOGY AS A SCIENCE
“Hydrology is the science that
treats the waters of the earth, their
occurrence, circulation and
distribution, their chemical and
physical properties, and their
reaction with their environment,
including their relation to living
things. The domain of hydrology
embraces the full life history of
water on the earth” The “Blue Book”
From “Opportunities in Hydrologic Science”, National Academies Press, 1992
http://www.nap.edu/catalog.php?record_id=1543
Has this definition evolved in recent years? Are new issues important?
A profession is a “calling requiring
specialized knowledge, which has as its
prime purpose the rendering of a public
service”
What hydrologists do:
Water use – water withdrawal and
instream uses
Water Control – flood and drought
mitigation
Pollution Control – point and nonpoint
sources
HYDROLOGY AS A
PROFESSION
Have these functions changed in recent years? Are priorities different now?
WHAT ARE THE
COMPONENTS OF THE
HYDROLOGIC CYCLE?
HYDROLOGIC CYCLE
HYDROLOGIC MEASUREMENTS
Want data to help understand weather patterns, help predict future
weather, design conservation structures, reduce NPS pollution, etc.
Precipitation – rain gage and/or snow gage
Accumulated snow – snow survey
Runoff – stream gages
Evaporation – pan, ET w/ lysimeters, sap flow meters
Groundwater levels – monitoring wells
Other important meteorological data for modeling and design:
Wind speed
Solar radiation
Temperature
GLOBAL WATER BALANCE (VOLUMETRIC)
Units are in volume per year relative to precipitation on
land (119,000 km3/yr) which is 100 units
Precipitation Atmospheric moisture flow Precipitation Evaporation
100 39 385 424
Evaporation
61
Surface Outflow
38
Land (148.7 km2) Ocean (361.3 km2)
(29% of earth area) Subsurface Outflow (71% of earth area)
1
What conclusions can we draw from these data?
DIGITAL ATLAS OF THE WORLD WATER BALANCE
(PRECIPITATION)
http://www.crwr.utexas.edu/gis/gishyd98/atlas/world.htm#animations
WATER BALANCE
INPUTS – OUTPUTS = CHANGE IN
STORAGE
Precipitation Evaporation
Runoff
Subsurface Flow
Storage Transpiration
Runoff
Irrigation
Deep Seepage
Infiltration
• Water Budget Volumes
• Ft3 (m3)
• Gal (L)
• Acre-feet (ac-ft)
• Inches (cm) over an area
GLOBAL WATER BALANCE
Precipitation Atmospheric moisture flow Precipitation Evaporation
800 mm (31 in) 316 mm (12 in) 1270 mm (50 in) 1400 mm (55 in)
Evaporation
480 mm (19 in)
Outflow
320 mm (12 in)
Land (148.7 km2) (Values relative to land Ocean (361.3 km2)
(29% of earth area) area) (71% of earth area)
What conclusions can we draw from these data?
Applied Hydrology, Table 1.1.2,
GLOBAL WATER RESOURCES
105,000 km3 or
0.0076% of total
water
RESIDENCE TIME
Residence time:
Average travel time for water to pass through a subsystem of the
hydrologic cycle
Tr = S/Q
Storage/flow rate
Residence time of global atmospheric moisture (Ex. 1.1.1)
Volume (storage) of atmospheric water: 12,900 km3
Flow rate of moisture from the atmosphere as precipitation = 577,000 km3/yr
Tr = 12,900/577,000 = 0.022 yr = 8.2 days
One reason why weather cannot be forecast accurately more than a few days
ahead!
EXAMPLE PROBLEM
How much irrigation is required
during the growing season if the crop
requires 850 mm of water for optimal
production? How many liters of
water will be pumped if the field is 10 Precipitation = 500 mm
ha?
Percolation Runoff = 15 mm
below root zone
50 mm
SOLUTION:
Inputs – Outputs = Change in Storage
Inputs = precipitation (500 mm) + irrigation (?)
Outputs = runoff (15 mm) and deep seepage (50 mm)
Change in storage = Water required by plants (850 mm)
(500 + I) – (15 + 50) = 850
Irrigation = 415 mm
Liters of water = 415 mm * 10 ha
= 0.415 m * 100,000 m2
= 41500 m3 = 41,500,000 L
Electrons desired
“s” shell – 2
“p” shell – 8
Total – 10
Electrons available:
Hydrogen H1 – 1
Oxygen O16 – 8
For H2O – 10
WATER MOLECULE
http://www.brooklyn.cuny.edu/bc/ahp/SDgraphics/PSgraphics/SD.PS.LG.Water.html
POLAR BONDING
10– 50 times weaker
than covalent bonds
between atoms in a
molecule
Water as a solvent --
more substances
dissolve in greater
quantities in water than
in any other liquid
http://www1.lsbu.ac.uk/water/hbond.html
Water as a solid
(ice) is less dense
than it is as a liquid
Maximum density is
at 4°C
WATER DENSITY
http://www.chem1.com/acad/sci/aboutwater.html
END
-NLB
