FLOOD09199

• County: Statewide
• Basin: Statewide
• Title: HEC-2 Water Surface Profiles - Users Manual
• Date: 11/1/1976
• Prepared For: US
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

NINV on card Jl equal to 1 and entering the known water surface elevation as
variable WSELK on card X2 for each cross section. lfhen an adverse slope is
encountered, computations restart using n-values from the previous section,
but WTN computations continue.

(2) Another method is to specify the discharge and an assumed set
of "n" values, and have the program compute a water surface profile which
can be compared with the high water profile. For this method WSELK may be
input on card X2, without entering the computations, so that it can be
easily compared with the computed water surface elevation on the output.

g. Multiple Stream Profiles. The water surface profile computations
may be computed up both forks of a river or throughout a whole river basin
for single or multiple profiles in a single computer run. The profile is
first computed for reach 1 from the most downstream point to the end of
one tributary. The data for a second tributary (reach 2), whose starting
water surface elevation was determined when reach 1 was calculated, follows
the data for reach 1 except that the first field of the Xl card (section
number) is negative and is equal to the section number in reach 1 where'
the starting water surface elevation for reach 2 was determined. When
a negative section number is encountered, the program will search its
memory for the computed water surface elevation that corresponds to the
negative section number. It will then start computing the profile for
reach 2 with the previously determined water surface elevation.

h. Storage-outflow Data. Punched cards can be obtained from HEC-2
for stream routing by the Modified PuIs Method using program HEC-l. The
cards punched are Y,2 and 3 cards (see program description for HEC-l).
This option can be used only if multiple profiles are computed from the
same cross sectional data and if the summary printout is requested.
Interpolated cross sections determined by the computer may be used.
Routing reach sections may not be interpolated sections. However, it
may not be wise to use interpolated cross sections since a different
number of cross sections might be interpolated between two given cross
sections for different magnitudes of dischsrge which could cause
inconsistencies in the incremental storage volumes. The ability to
repeat the previous cross section by using only an Xl card (i.e., field
2 on the Xl card is blank) can be used where additional cross sections
are needed at the ends of routing reaches and in place of the interpolated
cross sections. The J4 card calls for this option.

i. Critical Depth Computation. Critical depth will not be computed
for all cross sections in this program unless that option is requested on
the J2 card, since this takes about half of the computation time. However,
the program will check each cross section to see if the depth is close to
critical. If the depth is near critical, it will calculate critical depth
using subroutine DC by determining the point of minimum specific energy using
a discharge weighted velocity head. Critical depth will always be computed
for supercritical profile and it will be determined for low flow for the
cross section upstream of a special bridge. This low flow critical depth
is calculated by subroutine YCRIT for a trapezoidal section.

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