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Full Equations Utilities (FEQUTL) Model for the Approximation of Hydraulic Characteristics of Open Channels and Control Structures During Unsteady Flow


5.1 Standard Header Block

The standard header block must always appear first in the input to FEQUTL. It defines the command names used in FEQUTL to process the subsequent input. Some values and options that control command processing in FEQUTL also are defined. The command names are changed infrequently, usually only when a new version of the software is released. Therefore, the common practice is to copy the standard header block from an available input file.

The number to the right of each command name in the standard header block is an internal control number for FEQUTL. The number must not be changed. The number is used to access the part of FEQUTL that completes the operations defined by the command. Changing the name of the command is inconsequential, but changing the internal control number changes the command drastically.

The lines in the standard header block are as follows.

         UNITS= ENGLISH      (or METRIC )Selects measurement units.
         NCMD= 24            Number of commands present in standard header block     
         FEQX 1
         FLOODWAY 2
         BRIDGE 3
         CULVERT 4
         FINISH 5
         FEQXLST 8
         SEWER 10
         MULPIPES 11
         FTABIN 12
         EMBANKQ 13
         CRITQ 15
         GRITTER 16
         MULCON 18
         CHANRAT 19
         EXPCON 20
         HEC2X 21
         QCLIMIT 22
         XSINTERP 23
         FEQXEXT 25
         CHANNEL 26
         WSPROX 27
         WSPROQZ 28
         WSPROT14 29
         UFGATE 30
         DZLIM= 1.0       Minimum water-surface height increment in output table; must be >0
         NRZERO= 0.08     Minimum nonzero water-surface height in the table; must be > 0
         USGSBETA=NO      Selection of computation of This is the Greek letter Alpha and This is the Greek letter Beta
         EPSARG=4.E5      Convergence criterion for CULVERT, EXPCON
         EPSF=1.E4        Convergence criterion for CULVERT, EXPCON
         EXTEND=NO        Cross-section extension option.

DZLIM and NRZERO are used to control the spacing of the water-surface heights argument values in cross-section tables. The list of water-surface heights in a cross-section table is first developed from the unique water-surface heights values defined by the breakpoints along the boundary of the cross section. This list is then checked for an argument near zero. If no argument near zero is available, the value given by NRZERO is inserted as an argument. The list of arguments also is checked to ensure that the interval between successive arguments in the table is never greater than DZLIM. Both of these parameters are provided to help control the errors of interpolation in conveyance for the cross section. The near-zero point is needed because the conveyance varies rapidly near zero water-surface height, and linear interpolation in the square root of conveyance at small water-surface heights is inaccurate if a near-zero argument is not in the table.

USGSBETA defines the method utilized in computing the momentum correction coefficient, This is the Greek letter Beta, and the energy-flux correction coefficient, This is the Greek letter Alpha, in a cross section. If USGSBETA=NO, then This is the Greek letter Beta= 1.0 and This is the Greek letter Alpha= 1.0 in each subsection of the cross section. If USGSBETA=YES, then the value of This is the Greek letter Beta and This is the Greek letter Alpha in each subsection are computed with the USGS method given in section 3.1.1.

EXTEND defines the procedure for extending or adjusting the channel boundary if the first and last point of a cross-section description are either not at the same elevation or are not the maximum elevation in the section. If EXTEND = YES, then a frictionless vertical extension of the channel boundary at either the first or last point, or both, is applied to match the maximum elevation found at any point in the cross section. The size of the extension is given in a warning message. If EXTEND=NO, then no extension is applied and the table is computed to the minimum of the elevations of the first and last point given on the boundary.

If one side of the cross section is extended in FEQUTL and then a water-surface elevation above the low side of the cross section is computed in FEQ, a warning message cannot be issued in FEQ simulation because only the cross-section table and not the cross section is considered in the FEQ computations. If the extension is large, the results from FEQ may be in error because a large part of the cross section is unknown. It is best to use EXTEND=NO and to manually adjust cross sections that have an inadequate vertical extent as determined in subsequent computations in FEQUTL or FEQ.

Examples of most commands and options for FEQUTL appear in the example input file FEQUTL.EXM. This file may be obtained by electronic retrieval from the World Wide Web (WWW) at http://water.usgs.gov/software/feq.html and by anonymous File Transfer Protocol (FTP) from water.usgs.gov in the pub/software/surface_water/feq directory.

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