Geoscience Reference
In-Depth Information
1000
Fig. 3.16 Intensity-duration-
frequency relationship
for Washington DC,
calculated with Equation
(3.3) and the constants
K
p
=
40,
a
=
0
.
2,
b
=
0
.
19 and
c
=
0
.
79.
100
100 y
50
25
10
5
2y
10
1
15
30 45 min
1
2 days
0.1
1
10
100
Duration D (h)
Double mass curve analysis can also be used to interpolate missing data (Paulhus
and Kohler, 1952), and it has been applied to other types of hydrologic data, such as
streamflow, sediment records and precipitation-runoff relations (Searcy and Hardison,
1960).
3.3.3
Runoff design rainfall data
For engineering design purposes, mainly related to the rational method or the unit hydro-
graph (see Chapter 12), point rainfall data are often organized according to the intensity,
the duration and the frequency of the storm events. Such analyses have been published
for many different locations. Hershfield (1961), Miller (1963) and Bruce (1968) have
published maps covering North America. Similar maps have been produced for other
regions of the world as well. Because rainfall-generating mechanisms can be quite sim-
ilar in different hydrologic regions, many attempts have been made to generalize this
type of information in the form of empirical functions. Some pertinent results can be
found, for example, in the studies by Bell (1969), Chen (1983), Ferreri and Ferro (1990),
Kothyari and Garde (1992), Ferro (1993), Pagliara and Viti (1993) and Alila (2000). This
topic continues to be the subject of research (see, for example, Madsen
et al
., 2002).
A widely used equation, whose evolution can be traced through the work of Meyer
(1917, p. 149), Sherman (1931) and Bernard (1932), can be written as follows
T
r
P
=
K
p
(3.3)
+
b
)
c
(
D
in which
P
is the intensity [L
T] of a rainfall episode of duration
D
[T] and with a return
period
T
r
(see Chapter 13), and
K
p
,
/
,
,
a
b
and
c
are constants for a given location.
Example 3.3. Intensity-duration-frequency relationship
Figure 3.16 shows an example of Equation (3.3) with the constants
K
p
=
40,
a
=
0
.
2,
h
−
1
,
D
in
b
=
0
.
19 h and
c
=
0
.
79
(with
P
in
mm
h,
and
T
r
in
years)
for
