Draw down radius through clay barrier

[lsp01]

I am trying to find an accepted method of calculating the draw down radius associated with a stormwater pond having a controled discharge set below the accepted groundwater table.

We are trying to reduce potential wetland impacts due to the lowering of the water table by introducing clay barrier wall along one side of the pond. Our problem is that the confining layer is to deep to efficiently key into. Since contamination is not an issue, some seepage is okay.

I have used the "Ponds" program by Seereeram to calculate drawdown for the pond without the clay barrier, but it doesn't consider varying permeabilities. The best we have come up with is pro-rating the permeability using the depth of the clay wall and the overall depth to the confining layer.

Has anyone else wrestled with this problem??

Laura P, P.E.

 

[BigH]

See Cedergren's book on Seepage, et al - or Terzaghi and Peck. That, my friend, is why we all learned to do flow diagrams for water seepage. You can adjust your flow diagram for various permeabilities as per notes in T&P. It is a hand calc - but you should be able to get a reasonable estimate.