Groundwater drawdown in swale?

[murdock]

Hello all,

I have been asked to estimate the extent of groundwater level drawdown for a proposed swale (2' deep) that extends through a wetland (presumed groundwater elevation 6" below grade). The regulator is asking for an area around the swale that will have a lowered water table elevation due to this feature.

I haven't found a set of equations that match my needs exactly, I have seen the Theis equation that determines the cone of depression for a water well, and thought my case could be approximated by this condition.

Has anyone else had experience in answering this question?

Regards,

- smm

 

[fattdad]

Consider boundary condition shown on page 4-2

http://armypubs.army.mil/eng/DR_pubs/DR_a/pdf/tm5_818_5.pdf

There's a parameter "L," which you can estimate using page 4-24. Please note that permeability on the equation of 4-24 is in units of 10-4 cm/sec.

The length of zero drawdown is a function of permeability. Get some grain-size data (or run a field test to evaluate). If using grain-size data, here's something that may help:

http://home.comcast.net/~fatt-dad/permeability_correlation.pdf

Please note on the graph that permeability is also shown in units of 10-4 cm/sec.

You may want to consider all flow-to-slot equations if 4-2 doesn't quite work. That reference is a great document.

f-d

¡papá gordo ain’t no madre flaca!