CHECK-RAS Exercise

Computation of encroachment stations at structures.

There are some messages in CHECK-RAS that do not provide the solution because at the time of release of CHECK-RAS the solution to the problem was not yet established. One of the messages is the FW FW 02 message; you will see the following:

RS: 5380


FW FW 02 Encroachment method is 4. However, encroachment stations are not computed at this river station. Please investigate the problem.

When you highlight the message number FW FW 02, the following help information is displayed:

Help:

CHECK-RAS cannot find the left and right encroachment stations in the User Table, CHECKRAS. Please investigate why HEC-RAS may not compute the encroachment stations. However, this message will not be checked at the culvert and inline weir because HEC-RAS did not provide the encroachment stations at these structures.

We will provide one solution to this problem. The user is encouraged to inform us if there are other solutions to this problem. We will provide all solutions when CHECK-RAS is updated.

Please download the project file, plan files, geometric file, and flow file to your computer by clicking here.(WinZip format)

Problem

Please review plan 01 first by opening with the HEC-RAS program. Please open Steady Flow Analysis window, Options, and Encroachments. You will find that Encroachment Method 4 with a surcharge value of 1.0 was used at all the cross sections including the bridge cross section, which is at RS 5380. Section 2 of the bridge is at RS 5250 and Section 3 of the bridge is at RS 5385.

Please run this plan and open the Profile Output Table window, Standard Tables, Encroachment 1. Please select only the 100-year and floodway profiles from the Options menu and Profiles command. You will see the following:

At RS 5385, Top Width Act value for the floodway and the 100-year profiles are the same.


At RS 5385, 5380 BRU, and 5380 BRD, Enc Sta L and Enc Sta R are not computed.


At RS 5250, Enc Sta L is equal to Ch Sta L and Enc Sta R is equal to Ch Sta R.

HEC-RAS normally will use the encroachment stations at Section 2 of the structure as the encroachment stations at the bridge sections and Section 3 of the structure if encroachment method 4 is used at Section 2, Bridge Section, and Section 3. However, in this case the Enc Sta L of 561.77 and Enc Sta R of 616.74 at RS 5250 (Section 2) is within the channel bank stations of 558.86 and 639.25 of RS 5385, and RS 5380 BRU. Since encroachment stations are not allowed to compute within the channel bank stations when encroachment method 4 is used, HEC-RAS did not compute encroachment stations at RS 5385 and RS 5380.

Please generate the report file to check with the CHECK-RAS program. When generating the report file, please make sure that all the boxes in the Input Data are checked, all the boxes except Flow Distribution, and Summary of Errors, Warnings, and Notes are checked in the Output, and the Selected Summary Tables box has CHECKRAS as the only table. After closing the Report Generator window, please save the project.

Run the CHECK-RAS program. Select the project and extract the data. Select the profiles and select the floodway check button. Click the Yes button to the statement "You need to specify allowable surcharge ......".

Please review the report; you will see the message FW FW 02 at RS 5380. When you highlight the message FW FW 02, the Help message does not provide you with a solution at this time.

Solution

The solution is given in plan 02. In order for HEC-RAS to compute encroachment stations for this case, encroachment method 1 must be used at RS 5385 (Section 3) and RS 5380 (Bridge Section). Since the encroachment stations are at the channel bank stations at RS 5250 (Section 2) and the type of flow is pressure flow for the 100-year flood, the encroachment stations at RS 5385 and RS 5380 are set at the channel bank stations of these river stations.

Please open plan 02 in the Steady Flow Analysis window. Please use Options, Encroachments to review the encroachment stations. Encroachment Method 1 is specified at RS 5385 and RS 5380 and the Enc Sta L (Value 1) is equal to 558.86 and Enc Sta R (Value 2) is equal to 639.25.

Please run plan 02 and open the Profile Output Table window, Standard Tables, Encroachment 1. Please select only the 100-year and floodway profiles from the Options menu and Profiles command. You will notice the following:

At RS 5385, Top Width Act value for the floodway profile is smaller than the 100-year profile.


At RS 5385, 5380 BRU, and 5380 BRD, Enc Sta L and Enc Sta R are computed.

Since the surcharge values are not more than the allowable value of 1.00 and not less than -0.09, and the floodway widths seem to be transitioning from one river station to the other smoothly, the encroachment stations at RS 5385 and RS 5380 do not need to be adjusted further.

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Last Modified: Friday, 15-Jun-2007 11:57:20 EDT