Full Equations Utilities (FEQUTL) Model for the Approximation of Hydraulic Characteristics of Open Channels and Control Structures During Unsteady Flow
Purpose: Cross-section function tables containing the cross-section hydraulic characteristics needed in the FEQ model for simulating flow in a branch are computed in the FEQX command. Coordinate points on the boundary of the cross section are given in a fixed format.
Variable: TAB, CIN
Format: 7X, I5, A50
Example: TABLE #= 00025 MONOTONE SAVE22
|TAB is the table number that identifies the cross-section function
table computed from the cross-section boundary description specified in
the subsequent lines.
CIN is an alphanumeric field in which the user may specify several options after the table number. The options are as follows.
EXTEND: A vertical, frictionless extension is added to the first or last point of the cross section, as needed, to match the point of maximum elevation in the cross section.
MONOTONE: The offsets for the cross section are examined to ensure that they are increasing. This is useful in preliminary checking of cross sections for natural streams.
NEWBETA: The momentum-flux correction coefficient,, and the kinetic-energy-flux correction coefficient,, are computed by application of a method suggested by Schönfeld (1951) and discussed in section 3.1.2. The geometric mean of the critical flows estimated using the momentum and energy principles is tabulated in this option.
NEWBETAE: Same as NEWBETA except that the critical flow tabulated is based on the energy principle.
NEWBETAM: Same as NEWBETA except that the critical flow tabulated is based on the momentum principle.
NEWBETA, NEWBETAM, and NEWBETAE can only be used for cross sections that do not have converging boundaries. Thus, these options imply checking for monotonicity.
OLDBETA: The coefficients and for the cross section are computed from equations 7 and 8 in section 3.1.1. The velocity-distribution coefficients,i and i, in each subsection of the cross section in these equations are taken to be 1.0 if USGSBETA = NO in the Standard Header Block (section 5.1). If USGSBETA = YES, then these coefficients are estimated as described following equation 8 in section 3.1.1. In either case, the critical flow in the cross section is estimated as if the velocity distribution coefficients are both 1. Thus, critical flow is computed ignoring the effect of velocity distribution.
SAVEnn: A copy of the resulting table is saved internally in the FEQUTL
computations in type nn format, where nn gives the two-digit table type
with the valid range from 20 to 25.
NOSAVE: A copy of the table is not saved internally in the FEQUTL computations. This is the default action if none of the save options are given.
OUTnn: A copy of the table is output to the standard function-table file in the Type nn format. If no output option is given, a cross-section function table of type 21 is output to the standard-function table file.
NOOUT: Output of the table to the standard function-table file is suppressed.
Variables: STAT, LEFT, RIGHT
Format: 8X, F10.0, 6X, F10.0, 7X, F10.0
Example: STATION = 8.256 LEFT = 100.0 RIGHT = 967.
|STAT is the station of the cross section.
LEFT is the offset on the left side of the cross section where a vertical frictionless wall is added in the computation of the cross section.
RIGHT is the offset on the right side of the cross section where a vertical frictionless wall is added in computation of the cross section.
Thus, encroachments on the cross section can be indicated without changing
the cross section. If LEFT RIGHT, then the encroachments
are not calculated. LEFT is set equal to RIGHT by default if the input
Variables: NAVM, SCALE, SHIFT
Format: 5X, I5, 7X, F10.0, 7X, F10.0
Example: NAVM = 00001 SCALE = 1.0 SHIFT = 0.2
|NAVM specifies the methodology for computing the effective roughness
of a compound cross section and also provides optional values for scaling
of the offsets and shifting of the elevations. If NAVM = 0, the
total conveyance is computed from the sum of the subsection conveyances
(given by equations 5 and 6). This is the method applied for most open
channels and results in the total discharge equal to the sum of the subsection
discharges. If NAVM = 1, a weighted-average Manning's n value
is computed with the wetted perimeter in each subsection as the weight.
The conveyance for the cross section is then computed with the weighted-average
n value. This is the method usually applied for closed conduits
with abrupt changes of roughness around the perimeter and results in the
total discharge equal to an assumed uniform flow velocity times the flow
SCALE is multiplied with the offsets and can be applied to adjust for scaled measurements from a map. The default value is 1.
SHIFT is added to the elevation of each point on the boundary of the cross section. The default value is 0.
|NSUB is the number of subsections. The valid range for NSUB is from
1 to 96.
N( i ) is Manning's n for each subsection for the cross section.
The divisions between subsections are defined by frictionless, vertical lines. If variations in Manning's n with depth are required, the FEQXEXT command (section 5.9) must be applied.
|HEAD is a user-defined heading to describe the information on subsequent lines.|
|X( i ) is the offset of the coordinate point i on the
boundary of the cross section.
Z( i ) is the elevation of the coordinate point i on the boundary of the cross section.
SB( i ) is the subsection number for the coordinate point i
on the boundary of the cross section. If SB( i ) is left blank or
zero, the subsection number from the previous point will be assigned to
the current point. The last point on the cross-section boundary is indicated
by a subsection number
The boundary is assumed to be adequately defined by connecting these coordinate points with straight lines. The input for a point applies to the line segment connecting that point to the next point. Thus, a subsection assignment is not needed for the last point because no line segment connects it and a subsequent point. Therefore, the subsection for the last point is used as a flag to signal the end of the cross-section specification.
A closed-conduit section can be specified by defining the offsets and
elevations of points around the perimeter of the section. The description
should begin at the high point of the section and should not close completely
so that a free surface remains. The closed-conduit section should be traversed
in a counterclockwise direction when specifying points on the boundary.