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

Purpose: A 2-D table for flows through a short, prismatic channel that simulates the overbank flow bypassing a culvert or bridge opening is computed with the CHANRAT command. The rating for the flow through the channel resulting from the differences in water-surface elevation across it is given in the table. Additional discussion of this command is presented in section 3.3.

Notes: The results for each upstream head and partial free drop are
printed out with the CHANRAT command. Also printed is a column of values
headed by QDRERR, which is the same as the integration error tolerance
so long as no special problems result during computation. If the value
of QDRERR becomes large, this indicates that the stopping depth tolerances
are too small or that there is some error in the program.

LINE 1

Variable: TABLE

Format: 7X, I5

Example: TABLE *#=* 9900

Explanation:

TABLE gives table number for the table to be computed in FEQUTL. |

Variables: TABTYP, ERRKND, INTHOW, EPSINT, NDDABS, NDDREL

Format: A4,1X,I5,5A5

Example: TYPE

Explanation:

TABTYP gives the type of 2-D table to produce. Currently, tables of
type 6 and of type 13 can be computed in the CHANRAT command.
ERRKND specifies the error measure to apply in the adaptive integration.
An absolute error is selected if ERRKND INTHOW is the method utilized for integration. Simpson adaptive integration
is selected if INTHOW EPSINT is the tolerance value for the adaptive integration and has a default value of 0.1. This default value means that the estimated integration error must be less than 0.1 ft before computations are completed in the adaptive routine for numerical integration. NDDABS is the absolute deviation from normal depth used to control the integration near the singularity in the governing equation at normal depth. The default value for NDDABS is 0.005 ft. NDDREL is the relative deviation from normal depth used to control the integration near the singularity in the governing equation at normal depth. The default value for NDDREL is 0.005. |

Variables other than type are given default values if omitted. These
default values should be applied and changed only when necessary. These
defaults should be changed only with caution.

LINE 3

Variable: LABEL

Format: A5,1X,A50

Example: LABEL *=* Overbank flow at Golf Course Bridge on Dinky
Creek.

Explanation:

LABEL gives a user-defined label to identify the resulting table. |

Variable: XSTAB

Format: A6,1X,I5

Example: XSTAB

Explanation:

XSTAB gives the table number of the cross-section table defining the shape of the channel. This table must contain critical flow. Therefore, it must be type 22 or type 25. |

Variable: BOTSLP

Format: A6,1X,F10.0

Example: BOTSLP

Explanation:

BOTSLP gives the bottom slope of the channel with decline downstream taken as positive. The bottom slope may be negative or zero. The flow must be subcritical. If a flow is supercritical in CHANRAT, an error message will be issued and the rating table will not be computed. |

Variable: LENGTH, ELEV

Format: A6,1X,F10.0, 1X, 8X,F10.0

Example: LENGTH

Explanation:

LENGTH gives the length of the channel, which must be > 0.
ELEV gives the elevation of the midpoint. The elevation of the midpoint is used to compute the elevation for head to be stored in the table for later checking with the value given for elevation for head in FEQ when this table is used. The elevation for head is computed in FEQUTL as the maximum of the two end-point elevations computed from the given slope and one-half the length. In the current example, if the bottom slope was 0.005, the elevation for head would be 256.075. |

Variable: HEAD

Format: A80

Example: HEAD SEQUENCE FOR TABLE

Explanation:

HEAD gives a descriptive label for subsequent input. |

Variable: NFRAC

Format: 6X,I5

Example: NFRAC

Explanation:

NFRAC gives the number of partial free-drop fractions to use in computing the tail-water heads. A complete discussion of partial free-drop fractions for computation of 2-D function tables is given in section 11.2 of the documentation report for the Full Equations model (Franz and Melching, 1997). |

Variable: POWER

Format: 6X,F10.0

Example: POWER

Explanation:

POWER gives the power used to distribute the partial free drops from
0 to 1. The proportion of free drop is given by
i = 1, ..., NFRAC. |

Variable: HUVEC(I)

Format: F10.0

Explanation:

HUVEC gives the upstream heads to use in computing the 2-D table. The input of the list is terminated when a negative head is encountered. Head is measured from the end of the channel with the higher elevation. A nonzero head must result in a nonzero flow. Thus, if the bottom slope is positive, the datum for head is the upstream end of the channel; and if negative, the datum for head is the downstream end of the channel. |

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