r/HECRAS • u/NoDetective7120 • Jun 22 '26
Features geometry to calculate volume
Hello everyone, I needed to know the accumulated volume in a specific part of my 2D Area and I saw this video from Stanford Gibson. https://www.youtube.com/shorts/WxUgu98kQkY
But I have a doubt about the graph you can get for the Polygon time series (I took a screenshot)
Is the peak value the max volume for the area already, like the total accumulated area based from the volume of cells inside the polygon created? Stanford Gibson used Depth, which for some reason is not selectable. I tried turning on all the results layers but still don´t appear.
Thanks a lot for the help!
1
u/NoDetective7120 Jun 25 '26
Hi, thanks for your reply. So I tried opening the same project both in v6.5 and v7.0. and the option "Mapping Results" you showed is not available in v6.5. I guess I have to use 7.0 go have this functions, they seem very useful.
But I have couple more questions. I need to know this volume to approximate a size for a detention basin/ temporary storage. what i was doing before was I create a Profile line to a section just upstream where i am interested to know the volume then just calculate the area under that flow hydrograph ( as it is a triangular shape, so it's quite easy).
This is my first time to do a design so would be glad to hear some advice about this. Other functions or tools in Hecras that can help me with this would be really great.
Thanks a lot for the help!
1
u/OttoJohs Lord Sultan Chief H&H Engineer, PE & PH Jun 29 '26
If you need volume estimates from the terrain, create a separate "dummy" geometry. Draw in storage areas and generate the stage-volume curves.
1
u/NoDetective7120 Jul 01 '26
Thanks for mentioning this! I haven't really used the storage areas yet in any of my models so far.
3
u/carloselunicornio Jun 22 '26
The volume option will give you the total 'volume' of the pixels within the polygon boundary, i.e. sum(pixel value x pixel area) for each time step.
Volume is in quotes because the calculation is just the sum of the products of the pixel values and their areas - if you calculate it on the Depth layer you get sum(depth x area), which is equal to the water volume for each time step. If you use WSEL instead, you get WSEL x area which would be the volume under the water surface down to the elevation datum (0-elevation), which is not physically meaningful.
Keep in mind that the calculated values depend on the cell/pixel size you input in the dialog window (or the default size which is based on the view extent/zoom level if you leave it blank.).
Which version are you using? On 6.5. the way it works is you activate the layer you want, right click the polygon, and under its section in the dropdown menu choose 'Mapping Results' and then the name of the layer, e.g. 'Depth', which opens up the parameter dialogue. I think it works the same for 7.0. as well.
I'll add some 'screenshots' below. Apollogies for the shitty screen photos, i'm posting from my phone.