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Enhancements and Modifications to the Full Equations (FEQ) 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 13.3, Tributary Area Block--Tributary Area Tables, Franz and Melching (1997a), p. 164

Section 13.3 Tributary Area Block--Tributary Area Tables

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The tributary area is only required when the model is to compute lateral inflows to branches or level-pool reservoirs. FEQ computes the lateral inflows from the product of an area tributary to a computational element and a unit-area runoff intensity for that area. The input described below must define where FEQ is to find the data for the unit-area runoff intensities, what is the distribution of tributary area among the computational elements, and which unit-area runoff intensities is to be used for each element's tributary area.

For conceptual convenience the tributary area in an unsteady flow model for FEQ is broken into subareas based on the rainfall data used to estimate the unit-area runoff intensities. This reflects the reality that a single rain gage must be used to represent the temporal rainfall pattern over an extensive land area even though the surface conditions vary widely. Each surface condition will have a different time series of unit-area runoff intensity even though the same time series of rainfall data is used in the rainfall-runoff computations. FEQ groups the various time series of unit-area runoff intensity derived from a rain gage under the concept of a gage number, assigned by the user to the rain gage. For example, if two rain gages, say one at Wheaton and the other at O'Hare airport are used, the user could assign gage 1 to Wheaton and gage 2 to O'Hare. The watershed area assigned to Wheaton might have three different time series of runoff, one for impervious surfaces, one for forested surfaces, and the last for surfaces covered with grass. All three time series are implied by gage number 1 when the number is used in subsequent input. Although the user assigns gage numbers they must start at 1 and be consecutive thereafter.

The first part of the tributary area input relates gage numbers to the source of the time series data in the computer system. Two sources for the unit-area runoff intensities are supported by FEQ. They are selected by the value given to DIFFUS in the Run Control Block.

If DIFFUS=YES, then the source of the unit-area runoff intensity time series is a Diffuse Time-Series File (DTSF) that contains the time series for all land use and gage combinations. A DTSF stores multiple runoff events each with its own starting and ending times. These values over ride the starting and ending times given in the Run Control Block. Furthermore, FEQ will automatically compute the conditions in a dummy event, the first event stored in the DTSF. This event will always be computed to set the initial conditions to be used by all subsequent events in the DTSF. Provision is made for storing summary results from each event in a flood frequency file for later analysis.

On the other hand if DIFFUS=DSS, then the source of the unit-area runoff intensities is one or more HEC DSS files. A HEC DSS pathname defines one time series so that if there are 20 land-use and gage combinations there will be 20 different path names required to define the unit-area runoff intensities. The data type for these path names must be PER-CUM. The time series must be regular-interval time series and all time series must have the same time step. The units of the data are assumed to be in inches per interval but FEQ does not make use of the HEC DSS UNITS field at this time. The structure of the HEC DSS does not permit storage of starting and ending times as does the DTSF. Therefore the starting and ending times given in the Run Control Block are retained and only one event is run. No flood frequency file is used because only one event is run at a time.

The second part of the tributary area input defines the distribution of tributary area across computational elements. This distribution is independent of the source of the runoff intensities and is discussed after the two alternative sources for runoff intensity are described.

If DIFFUS=YES Return to section 13.3 Tributary Area Block--Tributary
Area Tables, and Melching (1997a), p. 164

LINE 1

Variable: TSFDSN, TSFNAM
Format: 7X, I5, A64
Example: TSFDSN=00012\SALT\TSFLONG
Explanation:
Supplies the FORTRAN unit number and name for the DTSF giving the unit-area runoff intensities on the tributary areas. If TSFNAM is non-blank, FEQ will attempt to open a file with name given by the contents of TSFNAM (most micro-computers) as the DTSF. On IBM mainframes the name given by TSFNAM will be the ddname for the DD statement defining the dataset. If the TSFNAM is blank IBM mainframes will attempt an implicit open if the proper DD statement defining the unit number given by TSFDSN is present. Some micro-computer environments will prompt the user for the file name in this case and some will abort execution. The unit number can be omitted and if it is given FEQ will not use the value. The unit number field is retained for consistency with old input files. Only the file name needs to be given.

LINE 2
Variable: FFFDSN, FFFNAM
Format: 7X, I5, A32
Example: FFFDSN=00011\SALT\UPMS\FFF
Explanation:
Supplies the FORTRAN unit number for the file to be used to store the flows and stages required for making a flood frequency analysis. If FFFNAM is non-blank, FEQ will attempt to open a file with name given by the contents of FFFNAM (most micro-computers) to store the values needed for flood frequency analysis. On IBM mainframes the name given by FFFNAM will be the ddname for the DD statement defining the dataset. If the FFFNAM is blank IBM mainframes will attempt an implicit open if the proper DD statement defining the unit number given by FFFDSN is present. Some micro-computer environments will prompt the user for the file name in this case and some will abort execution. The unit number can be omitted and if it is given FEQ will not use the value. The unit number field is retained for consistency with old input files. Only the file name needs to be given.

LINE 3
Variable: NLUSE
Format: 6X, I5
Example: NLUSE=00006
Explanation:
Gives the number of cover type/land uses and rain gage combinations represented by the tributary areas. For example, if there are three land uses in each of two segments in the hydrologic simulation then NLUSE=6. The maximum number of diffuse tributary areas allowed in FEQ is specified in the parameter MNDIFA and MXGLU in the INCLUDE file ARSIZE.PRM. The current number of land uses per gage is 12.

LINE 4
Variable: NGAGE
Format: 6X, I5
Example: NGAGE=00003
Explanation:
Gives the number of gages used to define the runoff intensities on the tributary area for the watershed.

LINE 5
Variable: HEAD
Format: A80
Example: GAGE NCOV
Explanation:
Heading for the gage number cover type table.

LINE 6 (one for each raingage)
Variable: GAGE, NCOV
Format: 2I5
Explanation:
Gives the gage number (in ascending order) and its number of cover types. There must be a line for each gage and the sum of the number of cover types must be the same as the value of NLUSE given on line 3. Line 6 is repeated as required to specify the number of cover types for each gage subarea in the watershed.
FEQ assumes that the runoff intensities in each record of the DTSF are stored in the order given here. The order is under the control of the user but a logical ordering should be used because the order of input for tributary area is tied to the order of appearance of the runoff values in the DTSF. Giving the runoff values in land-cover-type order for each gage has worked well in the past.

Back to Franz and Melching (1997a), p. 166 for lines 7-9