WSPC03077

• File Number: 8062
• Description: Federal Water Rights - Colorado Litigation - National Forest ISF Claims - Division 2
• State: CO
• Basin: Statewide
• Date: 1/1/1996
• Author: CWCB
• Title: Materials of Interest - Development of Instream Flow Recommendations in Colorado Using R2CROSS - CWCB
• Water Supply Pro - Doc Type: Report/Study

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001951

Appendix A - Program Calculations

Some R2CROSS users may be
interested in the operation and layout of the
Lotus 1-2-3 macro, Figure L depicts the
sequence of operations performed within each
R2CROSS menu option. Figure M provides the
layout of the R2CROSS macro within the Lotus
I -2-3 worksheet. The four major computations
performed within the R2CROSS macro are sag-
tape corrections, estimation of Manning's "n",
calculation of a water line comparison table,
and calculation of a staging table.

Sal1- Tl\Pe Calculations,
Channel geometry measurements that
are taken using the sag-tape methodology must
be corrected to a level reference. R2CROSS
uses catenary curve formulas to compute these
corrections from a sagging tape that has been
leveled at each end, The use of the catenary
curve solution is based on the assumption that
the suspended, steel tape is analogous to, a'
suspended cable placed under a unidirectionaIly
distributed load (Laursen 1978),
The derivation of the catenary curve
solution is beyond the scope of this manuscript.
Basically, R2CROSS uses the length of tape in
suspension, the tension applied to the tape, and
the standard weight of one foot of tape to apply
the necessary vertical distance corrections to
each cell vertical within the cross section.
When using a level and stadia rod to
survey channel geometry, the tape weight and
tension defaults, supplied in the original
R2CROSS,WK4 worksheet, will simulate an

extremely light tape stretched at very high
tension. This results in a sag correction of
approximately zero at each cell vertical,

Use of Manninl1's EQJIation,
Manning's equation is defined as:

Q - 1.486*A*R2I3*SI/2
n
where;
Q = discharge (cfs);
A = cross-sectional area (fe);
R = hydraulic radius (ft);
S = slope (ftIft); and
n = Manning's "n", a dimensionless
coefficient of roughness.

Manning's equation is used in two
separate R2CROSS calculations, It is fust used
within the "Verify" option to provide an initial
estimate of Manning's "n" using the rearranged
equation:
n = 1.486* A *R 213* S 1/2
Q
The parameters Q, A, R, and S are I
calculated from the raw field data and used to
solve directly for "n" (Figures G and J). Once
estimated, Manning's "n" remains constant
throughout the remainder of the streamflow
modeling.
Manning's equation is also used within
the "Calculate" option to solve for Q at each
simulated water surface elevation within the
staging table (Table 4).

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