Karst Geology – Underground flow

[SeanWatt]

Hi, a portion of the creek I’m modeling disappears into karst geology for about 400 m. There is a small surface channel which is wet only during high flow periods. Previous modeling of this creek appears to ignore the karst flow, and route everything through the surface channel. While that is an option, I’d like to explore two other options, and was wondering whether anyone had experience with these options.

1) Build a pipe into the model.

2) Build a “sink” into the model and disappear the flow, and then add it back in where it reappears in the channel.

3) I suppose there is a third option, to just reassign the flow using the flow plan data, but I’m not sure how RAS will accept this, or whether it will. Though this might just be how #2 actually works.

The other problem, of course, is that I don’t yet have a finite idea on what the flow split really should be, and that could be something I have to monitor over a couple of years, and revise the model at a later date.

Thanks,

Sean

[Chris G.]

You could simply use a uniform lateral inflow (use negative flow values to simulate flow leaving the system), or even explore the use of the groundwater internal boundary option. In any case, RAS is not a ground water model and you really should have a good idea of what is leaving the system through the Karst, before you put too muchy stock into the RAS results.

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