This program reads cross-section files and the corresponding MXS files (please see the material on Sections in Chapter 6 of this manual) and creates input files that can be used to run the HEC-RAS program for river analysis. The HEC-RAS program could be considered to be an advanced Windows-based version of the HEC-2 program. This program makes it easier for CADD and GIS systems to import their data directly for river network analysis. It is also very convenient because the output from the program can be exported directly to CADD programs where this data can be used to create water surface models for inundation mapping.
Data Format
HEC-RAS input files consist of three data sections:
* A header, containing data relevant to all sections of the data in
the file.
* A description of the stream network, containing reach locations and
connectivity.
* A description of the model cross-sections, containing cross-section
location and geometric
data as well as additional HEC-RAS modeling information.
The header information is mainly for the purpose of identifying the project and is mostly not used by the program. The only important information needed by the program is the "Units" section and the value must be "ENGLISH" or "METRIC".
The network is modeled as a set of interconnected streams. Each stream is a set of interconnected reaches. Each reach, hence, MUST have a unique Stream ID and Reach ID.
The Stream Network section contains a series of Point Numbers and the corresponding coordinates. In addition, this section has information pertaining to each Reach. For each Reach, the following information is provided:
* Stream ID and Reach ID. These are 16 character alphanumeric
strings. Together these two
items uniquely identify a Reach.
* Starting (FROM or upstream) point and ending (TO or downstream) point
of the Reach.
The FROM point and TO point here are given by their Point Numbers, as
identified above.
* The coordinates on the Centerline of the Reach, starting with the
FROM point coordinates
and ending with the TO point coordinates.
The Cross-Sections portion of the input file contains data describing the geometric properties at each cross section in the network. The following information is provided at each Cross-Section:
* Stream and Reach ID, to identify which Reach the
Cross-Section is on.
* Station, position of the Cross-Section, relative to the
Stream. The Station is taken as the distance from the current
station to the end of the stream. For this purpose, the stream MUST
be drawn Downstream to Upstream. THIS IS THE MOST
FUNDAMENTAL REQUIREMENT OF THE PROGRAM. If the Stream
is drawn in the other direction, then, it must be reversed
using the command Reverse Polyline under
Edit>Polyline Utilities
* Cut Line: Series of point coordinates, identifying
the surface line of the Cross-Section. HEC-RAS identifies
the cross-sections as going from left to right as seen from upstream to
downstream. The user only needs to make sure that the
stream network is drawn in the right direction (downstream to
upstream); all other conventions are
taken care of by the program.
Modeling Guidelines
Some additional guidelines in drawing the river network in the CAD so
as to model correctly
for HEC-RAS:
* All the Reaches in the Stream Network must be connected at common End Points; disjointed Stream Networks are not allowed; Reaches must also NOT cross each other.
* Streams cannot contain parallel flow lines. If three reaches connect at a node or End Point, at the most TWO of them can have a common Stream ID. (Please note that a Reach is uniquely identified by a Reach ID and a Stream ID.)
* Cross-Section lines can cross a Reach line only once and cannot cross other X-section lines.
Program Execution
Before starting the "Prepare HEC-RAS Input File" command, all the
SCTfiles and
their corresponding MXS files should have been created for every Reach.
Points where
two streams meet would form a node in the stream network. Sections of a
stream between
such nodes should be modeled as a Reach. and drawn as a separate
polyline. Now, change
to the Civil Design Menu. The MXS file for each Reach is created
using the
command Input Edit Section Alignment under
the Sections pulldown menu. Based on any of
the methods for creating section files (described in chapter 6 of this
manual), the Section file
for the Reach is created. The user must manage the .MXS file and the
.SCT file
corresponding to each Reach. At this point, a Stream ID
and Reach ID may be assigned to every Reach, based on a convenient
naming
convention, which is entirely up to the user. These
IDs would be needed when creating the HEC-RAS input file.
The program starts by asking the user for the Header information. The user can input as much information in this dialog box as possible. The "Units" can be "Metric" or "English".
Next, the user will be prompted to enter the .MXS and .SCT file names, the Stream ID and Reach ID for each Reach that you wish to add to your model. The user can enter data (IDs and file names) for as many Reaches as wished. That is, the user can create input files for each Reach individually and import them individually into HEC-RAS or create a combined input file for all the Reaches in the Stream Network. This makes it very convenient to add more Reaches to the HEC-RAS model at a later stage or do the analysis for various sections separately. After entering as many Reaches as needed, the user presses "Exit" to stop entering any further Reaches and to continue with the program execution.
On pressing "Exit", the user is prompted for the Input HEC-RAS file to be created. HEC-RAS input files have a .GEO extension. When the file is chosen at the prompt, the program creates the input file for HEC-RAS. This file can be used to import geometric data into HEC-RAS, as described below. You must have HEC-RAS version 2.0 or higher installed on your computer.
After starting HEC-RAS, select "Geometric Data" from under the "Edit" pulldown menu. This brings up a Geometric data editor, complete with a CAD screen and various options. From the "File" pulldown menu of the Geometric data editor, choose the "Import Geometric Data > GIS Format" command. This brings up a file browser and allows you to choose a geometric data file. Choose the .GEO file just created. This should load the geometric data into HEC-RAS, which is then converted into a CAD format drawing and shows up in the Geometric Data Editor in the form of a Stream network, with EndPoint, Stream ID and Reach IDs, Cross Sections stationing information, along with directions of in each Reach.
At this point, the user can edit several aspects of the data where Carlson only provides default values. Specifically, the Bank Positions and overbank reach lengths can be adjusted here. In addition, the Manning's coefficient has to be entered for all the cross-sections for all the left, right and center flows. As of HEC-RAS release 2.0, there is no way to input a default value for the Manning's coefficient, but this situation may improve in future releases of HEC-RAS, in which case the Carlson program will be modified immediately.
Other data that needs to be modified is the location of the left and
right banks. By default, the
left bank is given to be at 0.45 times the cross-section length and the
right bank is given to be at
0.55 times the cross-section length. In order to correctly model the
channel geometry, the location of the banks must be accurately defined
for each cross-section. This can be done by clicking on
the "Cross-Sections" icon in the "Geometric Data Editor" or by clicking
with the left mouse on the
cross-section to be edited. This brings up all the geometric data
related to that particular
cross-section, which may be edited as required.
The left and right overbank lengths are defaulted to equal the centerline length ( which may not be equal in the case of a sharp bend in the stream). These values can also be edited in the same cross-section editor as mentioned above.
Geometric data can be stored by running "Save Geometric Data" from the "Geometric Data Editor". The file extension assigned for Geometric data files is *.g*, which means that successive geometric data files will be given file extensions in a numeric sequence, beginning with *.g01.
Information specific to each analysis can be entered in the "Steady Flow Data Editor", which can be brought up by selecting "Steady Flow Data" from the Edit pulldown menu of the main HEC-RAS window. The data that can be selected here are the number of profiles that need to be run, flow in each reach for each profile simulation and the Hydraulic boundary conditions at each Reach for each Profile simulation. This information is stored in a file with the extension *.f01 and so on for successive files.
Once all the geometric data and Steady flow data has been
entered, the simulation can be run
by selecting "Steady Flow Analysis" from the "Simulate" pulldown menu
in the main
HEC-RAS window. After selecting the type of flow condition
(sub-critical, super-critical or mixed), the user selects the "Compute"
button to complete the analysis. If there are errors or serious
warnings,
the program reports them in a text editor. Otherwise, the program
shells out to a DOS screen
and completes all the necessary calculations. Several options are
available for viewing and
editing output from the HEC-RAS program, which are best explained in
their manual.
Pulldown Menu Location: Watershed->HEC-Ras Water Surface
Model
Keyboard Commands: sct2ras
Prerequisite: Section data (.sct)
File Names: \lsp\sct2ras.lsp, \lsp\regrade.arx