HEC-RAS Floodway Encroachment Analysis

[Sdk444]

Hello all,

I'm working with Hec-Ras to perform a floodway encroachment analysis. I've followed the simple directions in the help manual. I've accessed the encroachment window via steady flow analysis. Once the window is open I have my offsets set to zero and I have it checked to do equal conveyance reduction. I select method 4 because I know my targeted increase (its 0.2 feet). I have two problems, (1) It won't let me select my first profile which is my 100-year flow, its fixed on my second profile which is my 10-year flow. The help menu says the analysis can only be performed on profiles 2 through 15 (or what ever numbers have been selected by the user in the flow data editor). While in the flow data editor I'm not sure how I can set my 100-year flow to be current. (2) After setting my range of station values and running the analysis I find that it has only run the analysis for 4 out of the 24 stations I selected.

Any help is much appreciated, thank you.

 

[Sdk444]

I got it to see the profile I wanted but now I can't seem to get any results coming through. I don't know what I'm doing wrong. I see others have posted about going to each cross section individually? I'm not sure what this means. If I'm not mistaken I'm supposed to see thick black lines on the cross sections representing the floodway right?

 

[debgallery]

I'm a little late on this but maybe it will help you in the future (or others with the same questions).

You say you're not seeing anything - I'm assuming you're looking at the Cross-section window. First, make sure you're showing the correct "plan" (right click and select "Plans"), also, make sure you're showing the correct profiles (same deal, right click and select "profiles"). You'll want to have you're hundred year and your floodway profiles.

Still not seeing the encroachments (thick black lines)? You're encroachment stations are probably outside of your water surface (so they're not really affecting anything - hence not showing up). This is where you would edit your cross-section encroachments individually. Go to the "Steady Flow Analysis" window and open the correct "Plan". Go to the "options" pull down window and select "Encroachments. You said you selected method 4, which should have given you some initial values. Now you want to import those values to Method 1 (make sure your River, Profile and Reach are correct before hitting the "Import to Method 1" button). Now value 1 and value 2 represent the left and right bank stations for each cross-section. You can change those manually then rerun your plan.

This is a very iterative process and will take a lot of back and forth. I usually keep the Profile Output Table open to Standard Table Encroachment 1 so I can see the change in water surface elevation easily - just make sure to hit the "Reload Data" button every time you rerun the plan.

If you're still stuck it might help to upload the HEC-RAS file.

 

[Sdk444]

Thanks so much for your response. I've gotten the encroachments to show up. As I mentioned in my first post I'm looking to see what the floodway would be with a 0.2 foot rise in water elevation. This should be the value (+0.2) I'm looking for in the Delta WS column of the Standard Encroachment 1 Output table right?

So having imported my values to Method 1 I now have a table of Value 1 and Value 2 columns. These are the values I'm assuming I can mess around with to get the Delta WS I'm looking for. And if I understand the encroachment lines correctly, my floodway is the distance between the vertical thick black lines?

I would gladly include the file but I'm not sure how to upload the variety of Hec-Ras files required for my model.

 

[debgallery]

Yes, you are correct, the floodway is the distance between the vertical black lines. Sounds like you're getting there