Hydrology BC ENV 3025
Units, dimensions, and conversions
Hydrological quantities
basic measurements (e.g. velocity of water in a stream, mass of water in a raingage)
derived quantities (discharge in a stream)
Units and dimensions
precipitation has the
dimension
length [L] and the
unit
cm or mm or inch
many quantities have a dimension that is some combination of these fundamental dimensions
in equations, the dimensions on both sides have to match
the most common system of units employed today is the SI (System International d'Unites)
Quantity
Dimension
Unit
SI Symbol
Formula
Base units:
length
[L]
meter
m
mass
[M]
kilogram
kg
temperature
[
Q
]
kelvin
K
time
[T]
second
s
Derived units:
area
[L
2
]
square meter
m
2
volume
[L
3
]
cubic meter
m
3
velocity
[L T
-
1
]
meter per second
m s
-
1
acceleration
[L T
-
2
]
meter per second squared
m s
-
2
density
[M L
-
3
]
kilogram per cubic meter
kg m
-
3
force
[M L T
-
2
]
newton
N
kg m s
-
2
pressure
[M L
-
1
T
-
2
]
pascal
Pa
N m
-
2
stress
[M L
-
1
T
-
2
]
pascal
Pa
N m
-
2
energy
[M L
2
T
-
2
]
joule
J
N·m
quantity of heat
[M L
2
T
-
2
]
joule
J
N·m
work
[M L
2
T
-
2
]
joule
J
N·m
power
[M L
2
T
-
3
]
watt
W
J s
-
1
viscosity, dynamic
[M L
-
1
T
-
1
]
pascal-second
Pa·s
viscosity, kinematic
[L
2
T
-
1
]
square meter per second
m
2
s
-
1
specific heat
[L
2
Q
-
1
T
-
2
]
joule per kilogram-kelvin
J kg
-
1
K
-
1
Table A1.1 Base and derived units relevant to hydrology in SI measurement
Significant figures and precision
no more digits than justified by the precision of a measurement should be presented
derived quantities should reflect the number of significant digits of the least relatively precise number involved in the calculation
Unit Conversions
how to perform unit concersions
for a list of the most common unit conversions, see this
Table
Resources
Hornberger G.M. et al. (1998) Elements of Physical Hydrology,
Appendix 1
.