Hydrology Lab #1 Units.
Just as hydrology has taken concepts from many fields and languages, the units
used in hydrology come from many sources.
It is common practice in the USA to use both
metric and U.S. units.
liter is 1 cubic decimeter hence there are 1,000 liters in a cubic meter. A
liter at STP weighs 1 kilogram or 2.205 pounds. There are 3.79 liters in a
A gallon contains the amount of ale the king
could drink at a single sitting and
weighs 8.33 pounds.
The cubic foot
7.480 gallons is also a unit of measure of volume of water and weighs 62.31 pounds.
feet per second (CFS) is a common unit of flow.
How thirsty are you?
average person needs something like 1-2 quarts of water a day,
although consumption could be much higher in hot arid areas.
during fraternity parties (of beer anyway)
are therefore good units for individual water consumption.
How thirsty is your toilet?
typical consumption of water in residential settings is closer to 100 gallons
per day per person.
gallons is not a very convenient unit for measuring municipal water use.
How thirsty is your cotton crop?
consumes far more water than municipal uses, so gallons are rarely used for
measuring agricultural water use.
Rather the acre foot is the
common measure for large quantities of water and is approximately 325,851
is the volume of water that will cover one acre of land to the depth of one
foot. It is equal to 43,560 cubic feet of water.
Calculation I. Is water cheaper than dirt:
farmers pay as little as $5 per acre foot for water delivered from federal
water projects to their farms. How many pounds of water does a farmer get for a
Cost per pound.
acre equals 43,560 square feet, 1 acre foot equals 43,560 cubic feet of
water, a cubic foot of water weighs
62.31 pounds so an acre foot weighs 2,714223.6 pounds.
works out to 542,844 pounds of water delivered for a dollar.
that to dirt which for top soil would run about $5 per cubic yard (which would
weigh about 2,600 pounds) plus another $3 per cubic yard for delivery. So this
works out to about 325 pounds of dirt for $1 delivered.
dirt costs over 1,600 times as much as water per pound delivered.
Calculation II. What do you pay for water?
Huntsville today the rate for the first 0-3,000 gallons is $10.65. Then the
rate is $1.80 per thousand gallons.
the initial fixed fees this works out to 555.56 gallons per dollar or
alternatively $.002 per gallon.
If farmers paid what you do:
an acre foot would cost: 325,851 gal -3000 gal or 322,851 gal at $.002 per gal
or $645.70 plus $10.65 for the first 3,000 gallons or $656.35 per acre foot.
is more than 100 times what many farmers pay for water.
Example III. Residential consumption.
typical residential suburban family (i.e. has a lawn) uses about 1/3 of an acre
foot of water per year, about 75% for
typical alfalfa farmer uses 5-7 acre feet of water per acre per year and will
farm perhaps 640 acres.
would be equivalent to the water used by a typical town of about 10,000 people.
Gallons per day X 365 days = 65,700 gallons per year.
Acre feet X 640 acres = 3,840 acre feet per year X 329,250 gallons per acre
foot =12,3360,000 gallons/ 65,700 gallons per family
Island Hotel in Las Vegas employs 7,000 people and generates about $500 million
in revenues each year, it consumes 300 acre feet of fresh water per year (it
recycles its water for landscape irrigation).
The average small farmer
in Nevada that is growing an irrigated crop such as hay or alfalfa uses 2-10
times more water to support himself,
his family and some migrant labor.
Units of Flow:
measures of volume, measures of flow are most important in hydrology.
important measures of flow are Cubic foot per second (CFS) (which
is used for streams and rivers).
small stream might be 1-10 CFS a large river 100,000 or more CFS.
per minute (GPM) is the typical unit for production from wells. A
typical well will product 20-100 GPM while very large wells will produce 2000
or more GPM.
of gallons per day (MGD) is a typical unit for water treatment plants
and sewage treatment plants. A small plant might be 1-10 MGD while a large
plant might be 100-200 MGD.
meters per second is not as common in the U.S. but is common everywhere
Example V Flow in Harmon Creek
Harmon Creek has an average flow something
like 10 CFS.
many gallons is this in a second? A day
or a year?:
gal/cf x 10 cfs =
gallons per second.
day 60 sec/min x 60 min/hr x 24hr/day = 6,462,720 per day.
365 days per year = 2,358,892,800 gallons per year.
How much does this water weigh?
8.33 pounds per gallon this is:
Creek for sale?
I could own the flow in this creek and sell it in Huntsville at the Cities
rate what would it be worth?
gallons / 325,851 acre-feet/gal x $656.35/acre-foot =
of water velocity are feet/sec or meters/sec and
of stage height are feet or meters.
are also units of concentration, typically parts per million PPM or parts per
is the density of a substance relative to the density of water:
has a specific gravity of 1, solid rock and the particle matter in soil
typically has a specific gravity of 2.65, Gasoline has a specific gravity of
.75, PCB have a specific gravity of 1.6.
Example VI: Toxic transformers.
A transformer with
hazardous waste PCBs inside it:
Concentration of 480,000
ppm of PCB s and the other material is mineral oil with a specific gravity of
approximately .8. Volume of transformer is 900 gallon and it is 100 % full.
EPA wants to know what
is the weight in Kg of hazardous waste shipment?
x .48) + (.8 x .52)) 900 gal x 8.33Ibs/gal/2.205 lbs/kg.
+ .42) 1.19 x 900 gal. 1,071 x 8.33 =
8,921.43/2.205 = 4,046 kilograms.
should be reasonably able to convert between these units, since some exam
problems will involve calculations where you need to make simple unit
conversions (with supplied conversion factors).
meter = 3.281 feet.
mile = 5280 feet
kilometer = 1,000 meters = 1,000,000 mm.
cubic meter = 264.2 gallons.
cubic foot = 7.48 gallons, 28.32 liters.
liter = .2642 gallons.
acre foot = 325,851 gallons.
cubic meter per second = 35.32 cubic feet per second
cubic foot per second for 1 day = 1.98
Conversion factors metric to U.S. customary
hectare = 2.471 acres, 10,000 square meters.
acre = 43,560 square feet.
kg = 2.205 pounds.
cubic decimeter = 1 kg.
gallon = 8.33 pounds
cubic foot = 62.31 pounds
meter/sec = 2.237 mi/hr.
foot/sec = 1.097 km/hr.
inch of run-off per hour from one acre = 1 cubic foot per second of flow.