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Using correct water surface elevation for CE-QUAL-W2 bathymetry


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Hello all

I am getting confused with the way in which I need to create my bathymetry file in WMS for CE-QUAL-W2 in terms of the initial water surface elevation for my model run.

I have been provided a reservoir bathymetry map that was created when the reservoir was at a level of ~509 masl. This is in the form of a raster file from ArcGIS, and I have exported the data as an ASCII file and opened it as a DEM in WMS to be converted to a TIN (as recommended previously on this forum). Therefore the maximum elevation of the TIN in WMS is ~509 masl.

But this is not the maximum water surface elevation of the reservoir water level data (just the elevation at the time the DEM reservoir boundary was created), sometimes the water level goes up to ~511 masl. So my first question is how should I address this in WMS when setting up the CE-QUAL-W2 interface?

The second question refers to the CE-QUAL-W2 bathymetry input file created in WMS. When I follow the tutorial and set the 'top elevation' when calculating the rating curve, layers etc for the segments. What is the 'top elevation' exactly? Is it the maximum elevation of the TIN, the maximum elevation the water reaches during the model run, or in is my initial water surface elevation on the first day of the model run?

I.e. Should I be creating a new bathymetry input file in WMS each time I run the model depending on the initial water level on the day the model run starts?

Sorry it's long winded, but I'd be grateful for all guidance anybody can provide!!!

Many thanks

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I will have to think about this some, but I think you would want the maximum possible water surface elevation of the reservoir as the top elevation, so the dam crest elevation would be a good value to use. Maybe somebody else on the forum has more input on this though since I have not used the model in practice to know what most people use. If nobody replies, I'll check into this in more detail and get an answer for you.

You could combine your bathymetry data with readily available elevation data from the internet as long as a coordinate projection is defined for your bathymetry data. You should be able to use the Get Data tool in WMS to download a DEM for the area surrounding your reservoir and merge the DEM with the DEM containing your bathymetry data to create a single DEM. Then convert the resulting merged DEM to a TIN.

I do know that people usually create a single bathymetry file for a given reservoir, so that's what you should plan on doing.


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Hi Chris

Thank you for replying. I'll see if anybody else replies, if not then the dam crest elevation sounds like a good plan, although the dam crest elevation is actually lower than the maximum water level reached over a period when there was flooding, so there's data over the time while the reservoir levels itself out to maximum capacity.

If you do create a single bathymetry file for a given reservoir, then how do you change ELWS each time you run the model with a different starting date? If you just change it manually in the npt file, then won't the calculated widths of the cells need to also be adjusted?


Edited by JTerry
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I think you can just change the inital water surface elevation (ELWS) values without needing to change the cell widths, but you might want to try this to see if your results are reasonable. Scott Wells or Chris Berger at Portland State U might be able to answer your specific questions about the model also. WMS just writes out a constant value for ELWS and uses the top elevation specified in the Global Layer Parameters editor.

There are lots of CE-QUAL-W2 related resources available (such as cequalw2wiki.com, xmswiki.com, and especially the PSU CE-QUAL-W2 web pages and model and documentation downloads), but they are difficult to sift through to get your questions answered. I hope this helps. Let me know if I can help with anything else.


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