1. Hydrologic Overview &
Quantities
It is important to understand the big
picture when attempting to forecast.
This includes the interactive
components and hydrologic quantities.
3. The complexity of what we are trying to
accomplish….
Infiltration
Evaporation &
Condensation
The Water
Budget
Photosynthesis &
Respiration
Antecedent
Moisture
Conditions
Transpiration &
Interception
Variable Source
Area
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!
Basin Process
Representation
Infiltration
Excess Precip.
Interception
Storage
Time
Series
Time
Series
5. From A Basin View
Excess Precip.
Excess Precip.
Model
Basin “Routing”
Runoff
Stream Hydrograph
“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).
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....
Location of
Storage
Total Water
(acre-feet)
Percent of
Total
Percent of
Fresh
Residence
Time
(years)
Total water on
earth
1.033 x 1015 100.0
Oceans 1.0 x 1015 96.8
Total Fresh
Water
3.314 x 1013 3.2 100.0 6977
Ice and
Glaciers
2.475 x 1013 75.4 5210
Groundwater
Deep
4.62 x 1012 14.0 973
Groundwater
Shallow
3.63 x 1012 11.0 764
Lakes 9.9 x 1010 0.3 21
Biosphere 8.1 x 1010 0.24 17.1
Soil Moisture 1.98 x 1010 0.06 4.17
Atmosphere 1.155 x 1010 0.035 2.43
Rivers 9.9 x 1010 0.003 2.1
15. Units & Properties of Water
Property Symbol Value Comments
Density
(mass/volume)
~1.94 slugs/ft3
~ 1.0 g/cm3
Slug = lb*s2/ft
Specific Weight
(weight/volume)
62.4 Lbs/ft3
9.81 kN/m3
g
Specific Volume
Specific Gravity s.g. 1.0 for water
@ 32.9o F
s.g.fluid =
gfluid/gwater
Vapor Pressure ~0.4 psi Vapor pressure of
the fluid - not the
atmosphere
16. Some Common Unit Conversions
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
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 = HQ/550
• 1 hp = 550 ft*lb/sec = 0.7547 kilowatts
weight of water
H = head or elevation difference
Q = flow
Hydropower wants a lot of flow and
a full reservoir…..
