For such a recursive type calculation, computer computations reduce
the effort required. However, since this is a one-dimensional formulation
of the problem, it is possible to carry out the necessary computations
manually.
The March 1955 storm on Lake Erie is used to demonstrate the scheme.
A plan view of Lake Erie is shown in Figure 3-59. The width and crosssection area of the Lake are shown in Figure 3-60, mean bottom profile in
Figure 3-61, and wind and wind direction data for the March 1955 storm in
Figure 3-62.
In the following example problem computations are made at a single
spatial point where Q is evaluated at a distance of 3Ax from Buffalo
(Fig. 3-59) at a time when the wind speeds are approximately maximum.
Tables similar to Table 3-10 should be used in manual calculations.
************** EXAMPLE PROBLEM **************
GIVEN:
△x = 10 miles
△t = 0.2 hrs.
g = 79000 mi/hr2
K = 0.003
The wind at the new time level is 50.5 miles per hour and 6 = 4.0°.
The corresponding water surface widths for this section are b^i/2 = 26.3
miles and b£^3/2 3 21.0 miles. The values from preceding calculations at
the previous time level are
Q”
1+1
= 0.0707 mi?/hr
s”
,
=
1+1/ 2
3.32 ft.
sn bi+3/2 ' : 3.76 ft.
An
i+1/2
0.426 mi?
An
1+3/2 ' = 0.278 mi?
n
Di+l/2 s = 0.0162 mi.
D"+3/2 ■
' 0.0132 mi.
Also required is the value of
is given as +0.0915 mi?/hr.
from the previous spatial step which
3-134