PERMFILE106431

• Permit No: C1980005
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: HYMO MODEL
• Section_Exhibit Name: TAB 07 APPENDIX 7-6 ATTACHMENT 7-6-1
• Media Type: D
• Archive: No

i
Six hydrogtaphs can be stored in a HYMO
program at a time. The hydrographs aze identi-
fied by storage location numbers 1 through 6.
Therefore, the same storage location number
must be used for many hydrographs in a HYMO
program. This is especially true when routing is
done through large watersheds. However, no
more than six hydrographs aze ever needed at
one time because HYMO programs begin at the
head of a watershed and work downstream
through one reach at a time. When a storage
location number is used to store or compute
another hydrograph, the first hydmgraph is lost.
The user should be sure that the hydrograph will
not be referred to again before using the storage
location number for another command.
To store, compute, or route a hydrograph, the
user must specify the time increment. There aze
no rigid rules about selecting the time incre-
ment, but generally it should not be greater than
one-fifth of the time to the peak of the
hydrograph. This rule usually provides enough
points to adec)uately define the hydrograph. All
hydrographs aze limited to 300 points.
For the commands "STORE HYD," "COM-
PUTE HYD," "ADD HYD," "ROUTE," and
"ROUTE RESERVOIR," the user must specify
the number of the outflow hydrograph. The
hydrograph identification numbers aze used to
designate specific routing reaches, incremental
aeeas, reservoirs, and partial hydrographs. The
partial hydrograph number is given to all hydro-
graphs other than outflow hydtogtaphs from
reaches, incremental aeeas, or reservoirs. The
identification numbers for each group aze
Reaches .. 1-100
Partial hydrogtaphs ... .101-300
Incremental areas .301-500
Reservoirs ... .. .. .501+
Command Rules
The first command for any watershed is
START. The two data items associated with this
command aze the time ryinfall begins on the
watershed and a code for punching output data.
If a storm is to be routed through a watershed
only once, the punch code is deleted. However,
if more than one routing is to be performed, set
the punch code equal to a positive number, and
the output data for the first routing will be
punched for use in the second routing. More
than one routing is usually required.
Two commands, RECALL HYD and STORE
TRAVEL TIME, were designed to be computer
punched for second routings; consequently,
these commands do not appeaz in the table.
The STORE HYD command is used to store
the coordinates of a hydrograph in the com-
puter. It can be used for storing measured
hydrogtaphs or hydrographs computed by
methods other than the one used in FiYMO. The
irrput data required for STORE HYD aze storage
location number, hydrograph identification
number, time increment, watershed azea, and
flow rates of the hydrograph at the specified
time increment.
The CObIPUTE HYD command is used to
compute hydrographs from the incremental
areas of the watershed. The first five items of
data are storage location number, hydrograph
identification number, time increment, water-
shed azea, and SCS runoff curve number (3).
Normally, data items 6 and 7 aze watershed
height and main stem length. The height and
length aze used to compute the recession con-
stant Kand the time to peak tp . However, if K
and $ are known or estimated by some other
method, they can be entered directly into the
program. This is accomplished by placing a
minus sign before the values of K and tp and
entering them as data items 6 and 7, respective-
ly. The remaining data items aze values of the
mass rainfall at the specified time increment.
Since most watersheds have a limited number
of rain gages, the same mass rainfall data may be
used to develop several hydrographs. Once the
mass rainfall data have been entered in a
COMPUTE HYD command, they can be re-
peated for any number of COMPUTE HYD
commands without repunching the data.
Instead, punch a negative number for the eighth
data item of all COMPUTE HYD commands that
use the same rain gage. When data from another
rain gage are entered, the data from the first rain
gage aze lost and cannot be recalled by using the
negative number code.
The RECALL HYD command is one of the
two commands that aze computer punched.
When the punch code is a positive number, the
output from STORE IiYD and COMPUTE HYD
aze p,rnched on cards with the RECALL HYD
command. The RECALL HYD command stores
7-6-1-7

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