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[FEQUTL Update Contents]
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
5.3, CHANRAT command, Franz and Melching (1997b), p. 87
Section 5.3 CHANRAT Command
To
RELEASE.TXT
LINE 7
Variable: 
HEAD 
Format: 
A80 
Example:
HEAD SEQUENCE FOR TABLE
Explanation: Descriptive label
for subsequent input.
LINE 8
Variable: 
NFRAC 
Format: 
6X,I5 
Example: 
NFRAC= 21 
Explanation: 
Gives the number of partial freedrop
fractions to use in computing the tailwater heads. See discussion of twodimensional
function tables in Chapter 7, Program Structure and Function Table Definitions
in FEQ: A Modeling System for Unsteady FreeSurface Flow in a Network of
Channels, Franz (1996) for a discussion of partial free drops. 
LINE 9
Variable: 
POWER 
Format: 
6X,F10.0 
Example: 
POWER= 2.0 
Explanation: 
Gives the power used to distribute
the partial free drops from 0 to 1. The proportion of free drop is given
by 

for 
LINE 9a
Variable: 
LIPREC 
Format: 
7X,F10.0 
Example: 
LIPREC= 0.02 
Explanation: 
Optional input of the linear interpolation
precision to use as the target for automatic definition of the head sequence.
If LIPREC is not present, the following line, 9b, is not given either.
The head sequence must then be given in its entirety. If LIPREC is present,
then line 9b must be present and CHANRAT only uses two values of upstream
head. The first value is the minimum value of head and the last of the
two heads is the maximum value of head. If more than two heads are given
the first and last values are used. All intermediate values are skipped. 
LINE 9b
Variable: 
MINPFD 
Format: 
7X,F10.0 
Example: 
MINPFD= 0.01 
Explanation: 
Must appear if LIPREC line appears.
Gives the minimum value of partial free drop to use in the automatic assignment
of partial free drop values. 

Notes on automatic head selection:
The following considerations apply when LIPREC and MINPFD are used: 

1. When LIPREC and MINPFD are used,
NFRAC should have a value between 30 and 60. It is used to define a series
of upstream heads as well as partial free drops to use in defining the
final spacing to be used in the computations. 

2. POWER is not now used if automatic
head selection is requested. However, it may be used in the future and
is retained for consistency with past input. 

3. The desired interpolation precision
may not be met in all cases. Rapid changes in table value may not be detected. 

4. The default integration error tolerance
in CHANRAT is reduced to 0.05 if automatic head selection is requested.
If you explicitly set the integration error tolerance to a value different
than the default, that value will be used. The smaller tolerance is used
to get greater consistency in error estimates. Some of the lack of meeting
the error tolerance is a result of the other tolerances in the computations.
If they are too loose, erratic results, on the order of a fraction of a
per cent, result. However, this is often enough to be a large part of a
small relative error. Requesting relative errors smaller than 1 per cent
is not wise and may not work. 

5. MINPFD should not be too small.
0.01 is probably small enough. This often gives a factor of four or so
between the largest and smallest flow tabulated for a given upstream head.
A MINPFD of 0.005 or less will probably show many locations with LIPREC
exceeded. This is primarily the result of the difficulty of computing reliable
flows when the drop is small, sometimes less than oneten thousandth of
a foot! 

6. Using small minimum heads can result
in there being many upstream heads because free flow tends to increase
with head roughly proportional to the cube of the head. This requires close
spacing at small heads in order to maintain a small uniform relative error. 

7. If the errors reported in the output
are larger than LIPREC by significant amounts, try increasing NFRAC to
60 or so. Do not go much larger because internal space may be exhausted.
This can sometimes improve the results. 
Back
to Franz and Melching (1997b), p. 87, section 5.3, CHANRAT Command
To
update for new section 1.2.3a, Table Interpolation and Automatic Breakpoint
Procedure