To
RELEASE.TXT
Enhancements and Modifications to the Full Equations Utilities (FEQUTL)
Model, March 1995 to August 1999.
Note: This document is separate from the U.S. Geological Survey report by Franz and Melching (1997). This description of enhancements and modifications to the Full Equations Utilities Model has not been approved by the Director of the U.S. Geological Survey.
Input description update for section 5.1 Standard Header Block, Franz and Melching (1997b), p.79
Section 5.1 Standard Header Block
Support for refining the precision
of the constant in Manning's equation exists as an option in the Standard
Header Block. The constant, often given as
or
is the cube
root of the number of feet in a meter. The factor
is the default value if the optional input is left out because this was
the value used in previous versions. In the metric system of units, based
on historical usage and practice, the numeric value of the roughness coefficient
remains unchanged but the constant becomes 1.0 exactly. Apparently the
usage in the English system was derived from the metric system. The small
differences that arise when the approximate coefficient is used for the
English units make verification of the computation in metric units more
difficult. The differences are small but not so small as to be caused by
roundoff or truncation errors in the basic arithmetic operation on the
computer.
When making comparisons between computations
using metric and English units, the acceleration of gravity must be the
same in both sets of computations. A constant value of this acceleration
is adequate almost everywhere FEQ will be applied. The value of
is within a fraction of a per cent of the value normally encountered with
in the United States. However, provision has been added to compute the
gravitational acceleration as a function of latitude and elevation for
those rare cases when such effects might be important.
The optional input is as follows:
Variables: UNITS, NFAC_FLAG, LATITUDE, ELEVATION
Format: 8X,A8,1X,A8,F10.0,F10.0
Example: UNITS= ENGLISH EXACT 38.0 00.
Example: UNITS= ENGLISH
Explanation: Notice that there must
be two spaces following the equal sign before the specification of the
units response. The two responses are METRIC
and
ENGLISH.
The second example, saying nothing about either the factor in Manning's
equation or gravity, is the form used in previous versions and may continue
to be used. The first example shows how to request the exact value of the
factor (within the precision used in the computations) and at the same
time compute a value of gravitational acceleration. The first optional
input, NFAC_FLAG,
signals that the exact value for the factor in Manning's equation be used.
Any non-blank in the field will make that request. The value EXACT
is
given as a suggested value. The next optional input, LATITUDE,
is the latitude in degrees with positive values be north of the equator
and negative values be south of the equator. The final optional input,
ELEVATION,
is the elevation above sea level in feet (meters).
The first example above yields the
following output from FEQUTL:
FEQUTL uses:
NFAC= 1.485919 for Manning's equation.
GRAV= 32.1521 for g.
If we increase the elevation to 10,000
feet, about the highest elevation for application expected, we get
FEQUTL uses:
NFAC= 1.485919 for Manning's equation.
GRAV= 32.1211 for g.
The default values used in FEQUTL are : 32.2 and 1.49. The maximum relative error in gravitational acceleration for these two examples is about 0.26 per cent.
Back to Franz and Melching (1997b), p.79, Standard Header Block, section 5.1