FLOOD06611

• County: Elbert
• Basin: South Platte
• Title: Flood Prone Areas in Elbert County, Colorado - Technical Addendum
• Date: 1/1/1982
• Prepared For: Elbert County
• Prepared By: USGS
• Floodplain - Doc Type: Floodplain Report/Masterplan

ENTRY OF CROSS-SECTION DATA INTO COMPUTER

U.S. Geological Survey Computer Program E431, listed in "User's Manual, Com-
puter Applications for Step-Backwater and Floodway Analyses" (Shearman, 1976), was
used to calculate "individual cross-section hydraulic properties. First the cross-
section data obtained from field surveys were recorded on Form 1891A (see section
on "Backwater Analysis Coding Form"). A brief description of the 80-column data-'
input cards 1 isted on the form is as follows:

I
Card 1 gives the cross~section number, card number (ascending sequence numbers
must be assigned to each card 1, 3, 5, and 6 for each cross section), identi-
fies the stream by name, shows the quarter of the 7.5-minute topographic map
on which the cross section is located, gives the alphanumeric index code of '
the map, and provides the section, Township South, and Range West landline
description. Columns 65 and 66 specify a tolerance (TOL) of 0.02 ft in bal-
ancing the energy equation if step-backwater methods are used. Columns 68
and 69 (~h) specify that the hydraul ic values be printed at 0.2-ft intervals
above a selected base height (see card 3) so that straight-line interpolation
of data wi 11 provi de suffi ci ent accuracy. A Froude number (FN) of 1.0 was
entered in columns 71 and 72.

Card 2 is not needed for cross-section printout and can be omitted.

Card 3 describes the cross-section properties so that internal edit checks may be
made by the computer program. Included on the cards are: A specification
that the hydraul ic properties be printed out (col. 15). the number of survey
points (cols. 17-19), the number of subareas (cols. 21 and 22), and a desig-
nation of the base. height, or beginning elevation (cols. 24-27). Dummy values
in columns 35. 37. 38, 40. and 41 suppress error messages during the computer
program's internal editing process.

Card 4 is not needed for cross-section printout and can be omitted.

Card 5. Multiple cards 5 are used to input surveyed ground elevations. Five ele-
vations are listed per card. Data include horizontal station distances, in
feet (increasing from left to right), subarea "number, and elevations (without
the decimal point) in feet and tenths of feet. Data are right justified in
the appropriate field.

Card 6 provides Manning "n" channel-roughness information for the cross section.
The computer fields show (b) depth of flow below which a constant roughness
value may be applied and (a) depth of flow above which another "n"value ap-
plies. Depths (b) and (a) must be separated by at least 1 foot; interpolation'
between (b) and (a) occurs during computation.

These data were then punched on cards for entry into the computer.
of the card-input data for each of the 93 cross sections surveyed are
this report under "Computer Printouts of Card Images of Cross-Section
Streams in Elbert County, Colo."

P . ;
rlntouts
1 isted in
Data for

2