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Unformatted text preview: t this point the user should repeat these tasks until all of the encroachment
data are entered (i.e., for all the reaches and locations in the model, as well as
all of the profiles for which the user wants to perform the encroachment
analysis). Once all of the encroachment data are entered, the user presses the
OK button and the data will be applied and the window will close. The user
can return to the encroachment window and edit the data at any time. The
encroachment data are not saved to the hard disk at this time, they are only
saved in memory. To save the data to the hard disk, the user should either
select Save Project from the File menu of the main HEC-RAS window, or
10-5 Chapter 10 Performing a Floodway Encroachment Analysis select Save Plan from the File menu of the Steady Flow Analysis window.
The Import Method 1 option, allows the user to transfer the computed
encroachment stations from a previous run (output file) to the input data for a
future run. For example, if the user performs a preliminary encroachment
analysis using any of the methods 2 through 5, they may want to convert the
results from one of the runs to a method 1 encroachment method. This will
allow the user to further define the floodway, using method 1, without having
to enter all of the encroachment stations. The import of encroachment
stations, in this manner, is limited to the results of a single encroachment
profile for each reach. Performing The Floodplain Encroachment Analysis
The HEC-RAS floodway procedure is based on calculating a natural profile
(no encroachments) as the first profile of a multiple profile run. Subsequent
profiles are calculated with the various encroachment options available in the
In general, when performing a floodway analysis, encroachment methods 4
and 5 are normally used to get a first cut at the encroachment stations.
Recognizing that the initial floodway computations may provide changes in
water surface elevations greater, or less, than the "target" increase, initial
computer runs are usually made with several "target" values. The initial
computer results should then be analyzed for increases in water surface
elevations, changes in velocities, changes in top width, and other parameters.
Also, plotting the results with the X-Y-Z perspective plot, or onto a topo map,
is recommended. From these initial results, new estimates can be made and
After a few initial runs, the encroachment stations should become more
defined. Because portions of several computed profiles may be used, the
final computer runs are usually made with encroachment Method 1 defining
the specific encroachment stations at each cross section. Additional runs are
often made with Method 1, allowing the user to adjust encroachment stations
at specific cross sections to further define the floodway.
While the floodway analysis generally focuses on the change in water surface
elevation, it is important to remember that the floodway must be consistent
with local development plans and provide reasonable hydraulic transitions
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This note was uploaded on 03/16/2013 for the course ENGINEERIN 401 taught by Professor Tommas during the Spring '13 term at University of Alberta.
- Spring '13