FLOOD06423

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Preparation of Input Data for Automatic Computation of State-Discharge Relations at Culverts
• Date: 1/1/2000
• Prepared By: Matthai, Stull, Davidian
• Floodplain - Doc Type: Educational/Technical/Reference Information

AUTOMATIC COMPUTATION OF STAGE-DISCHARGE RI';LATIONS AT C\IIXEHTS 7

by types of flow and by entrance geometries.
The six flow types are divided into three
groups. each group having a discharge equa-
tion of the same general form. Thus, flow
types 1, 2. and 3 form one group; types 4
and 6 another; and type 5 the third. The coef-
ficient C is descriptive of the live- stream
"Contraction at the inlet and its subsequent ex-
pansion in the barrel of the culvert. Hence,
base coefficients for types 1, 2. and 3 flow
should be identical for identical geometri~s,
as should coefficients for types 4 and 6.

Entrance geometries have heen classified
in four general categories: (I) flush setting
in vertical headwall, (2) wingwall entrance,
(3) projecting entrance, and (4) mitered pipe
set flush with sloping embankment. These
four classes have been subdivided as nec-
essary in Bodhaine (1968), but they are all
comII?-on to the three flow-type groups.

Adjustment for Degree of Contraction

The degree of contraction may affect the
the value of the discharge coefficient if flow
is type 1, 2, or 3. The ratio of channel Con-
traction, m, is defined as (I - AI AI) where

A is the area of flow at the control section
(section 2 for type 1 flow, and section 3 for
lypes 2 and 3 flow). If m is less than 0.80,

the term (l/C2 - 1) in the equations for flow
types I, 2. and 3 is replaced during the com-
putation by

\ 0.64

I [0.784 - (0.98 - CHI -

!2... )]2
Al

I
1 ~ .
\

Office Computations

Plot a plan of the sit~ from th~ survey
notes (Benson and Dalrymple, 1967, p. 25)
and scale distances as needed. Select the
discharges and tail water elevations, and de-
termine discharge coefficients for -the range
anticipated. See more detailed instructions
in subsequent sections on the preparation of
data for cards 5, 6, and 7. If the headwater'
elevation for a particular low-head compu-
tation is higher than the ground elevation at
either end of the approach section. no result
will be obtained.

Preparation of Data

The program requires a complete and

.~

an"urale set of data for a 8uct"l'Hsflll ('ompu-
tation. If some hit of rt'quil~t"d inrol'mation
is lacking or ineorrcct.. the t"omputation will
generally he ahorted, though elTonpous an-
swers may be obtained depending upon tilt"
nature of the. input error. Careful attentioh
to instructions for completing the data shept
is essential. The reason for placing a digit
or a symbol in a particular column may not
be obvious. but these are instructions to the
computer to direct the sequence of operations
or to provide a reference identification.

Use Geological Survey form 9-1695.Stage-
Discharge Relations at Culverts (fig. 2), for
each culvert.

Only one form is needed for .a culvert if
up to 12 selected discharges and 10 tailwater
elevations will define the rating. A second
form with all data entered for all cards can
be used if more discharges or tail water ele-
vations are needed.

The cards are numbered 2 to 9 (there is
no card 1) in column 80 of the form; in the
following instructions, "card 2. II Ilcard 3, "
etc., refer to these numbers. Each card
has space for a sequence number of up to
five digits. The sequence numbers simplify
the arranging of punched cards in proper
order and will insure no mixing of cards be-
tween decks for several culverts. For a
given culvert problem, up to 12 cards. are
used, and these should be sequential within
the set, starting the first card (a card 2)
with any sequence number, and continuing
for that particular culvert by increasing se-
quence numbers for subsequent cards by 1.
A second culvert problem can start off with
any new sequence number for its card 2, and
this sequence number may be larger or
smaner than those in the previous culvert
problem.

In filling out the forms, care must be
taken to leave designated blank spaces blank
and to put no symbols in any space earmarked
for a decimal. All minus signs must occupy
a space alone, and may not be overpunched
with any other symhol.

Make all entries easily readable -- large,
clear, and dark. Use a dark pencil or ink.
If erasures must be made, make the cor-
rected entry legible. Do not cross Qut part
of an entry. Cross out the entire figure and
enter correct digits directly above those