Guide to Hydrological Practices, 6th edition, Volume I - Hydrology.nl

I.2-8
GUIDE TO HYDROLOGICAL PRACTICES
Table I.2.2. Recommended symbols, units and conversion factors
I II III IV V VI VII
Item Element Symbol
Recommended
Units
Also in use
Conversion
factor*
Remarks
1 Acceleration due to g m s –2 ft s –2 0.305 ISO
gravity
2 Albedo r Expressed as a decimal
3 Area (crosssectional)
(drainage
basin)
A m 2
km 2 ft 2
0.0929
acre
0.00405
ha
0.01
mile 2 2.59
4 Chemical quality mg l –1 ppm ~ 1 For dilute
solutions
5 Chezy coefficient
C m 1/2 s –1 ft 1/2 s –1 0.552 ISO
[v (R h
S) –1/2 ]
6 Conveyance K m 3 s –1 ft 3 s –1 0.0283 ISO
7 Degree day D Degree day Degree day Conversion
formula:
°C = 5/9
(°F–32)
ISO
ISO
Column IV
is based on
°C scale and
column V on
°F scale
8 Density p kg m –3 lb ft –3 16.0185 ISO
9 Depth, diameter,
thickness
10 Discharge (riverflow)
(wells)
(unit area–Q A –1 ,
or partial)
d
m
cm
11 Drawdown s m
cm
12 Dynamic viscosity
(absolute)
ft
in
0.305
2.54
Q
m 3 s –1
ft 3 s –1
0.0283
Q we
l s –1 gal (US) min –1 0.063
q m 3 s –1 km –2
l s –1 km -2 ft 3 s –1 mile –2 0.0109
10.9
ft 0.305
30.5
η N s m –2 ISO
Pa, s, kg m –1 s –1
also in use
13 Evaporation E mm in 25.4
14 Evapotranspiration ET mm in 25.4
15 Froude number Fr Dimensionless number ISO
16 Head, elevation z m ft 0.305 ISO
17 Head, pressure h p
m kg (force) cm –2
lb (force) in –2 10.00
0.705
18 Head, static (water
level) = z + h p
h
h
cm
m
ft 30.05
0.305
ISO
19 Head, total =
z + h p
+ h v
H m ft 0.305 ISO
20 Head, velocity
= v 2 (2g) –I h v
cm
m
ft 30.05
0.305
ISO
ISO
ISO