You have to ensure that your system is entirely saturated before.Then you have to verify if the in flow is almost the same as the outflow. It may be not very difficult to measure the flow in case of natural soil (not compacted). For the calculation you have to use the Darcy's law for multilayer.

You can inspire to these formula for your calculation

Great thanks, Cheers

This question may come to Mr.Andry Razakamanantsoa in such case effective porosity is concerned as supposed i have already known hydraulic conductivity. how do we flexibly measure the effective porosity in such case?

Effectively, the simple formulaes that i have proposed suppose that samples are not subject of volume change. It is not truly correct in the previews case but makes easier to estimate the relative value of permeability ( samples are constitued by gravel, sand...). But if you want to consider the effective porosity, then you have to consider the dry weight of each layer, in other term, this statement is true in case of compacted material. If you want to calculate the effective porosity with standard formulae in soil mechanics, In that case it is very important to be sure that each layer has a very low compressibility value (oedometric tests), and the hydraulic gradient is not very high to generate volume change and the last but not the least, samples must have a very low swellng pressure (near zero).

If there is not the case, the effective porosity calculation won't be so flexible. You have to consider the void ratio calculation as with the oedometric testing.

I guess effective porosity should be calculated using a conservative tracer test. You should measure the tracer concentration at several points and then use calibration to find it. Remember that in saturated flow, effective porosity is not used since these are calculated using specific yield or storage terms and the only place where effective porosity accounts for is the unsaturated flow (van genuchten equations) or the transport equations.

You might be seeing the droplet from the first valve but this doesn't mean that the column is totally saturated and the clay being on the second layer can work as an impermeable layer you need to saturated totally .Also you need to be sure that there is no air on the column cause air not only does not contribute to the flux but it also impedes it. ( Q=KA*(hi/z) ) hi=pressure height at the outflow measured from the free surface of water on top till the valve(i) and z = the height of the soil (the lenght from the start of the soil (not from the water above it ) till the end of the soil ->each valves height).Or Q/A =-u=K(dh/dz) (LT^-1) not so important for you i think .

In Peratometers of constant head (same water amount on the top of the column all the time ) we calculate k from K=VL/Ath ,Where V is the volume of water colected in time t , A = the cross-section of each speciment... the profile..., L= the samples length , and h the constant pressure ..the height from the top of the free water surface till the outlet ..valve..

In peratometers of moving ..(Failing head) we once fill a standart volume tube of water and we get it in touch with our speciments and we mesure then the drop of presure ... height on that tube thats h1-h2 in time t , so the type is k=(((rt^2)*L)/((ri^2)*t))ln(h1-h2) ,L= the lenght of the speciment , rt= the profile of the speciment , and ri = the profile ( cross section) of the tube t = time from h1 to go to h2 .see attached image

Ashutosh Singh , Could you provide me with a method of conservative trace test? and a bit specific description about it ? that would be awesome!!

for conservative tracer test you can use uranine. Lets say you start with uranine and u know that you have to measure the hydraulic conductivity and effective porosity of a field. Now you can have a continuous injection of uranine for 30 min or one hour. At the same time you measure the concentration of uranine at different locations in the field. Now as you know the flow and transport equations, you can make a model and find the hydraulic conductivity field and the effective porosity by minimizing the difference between the simulated and measured values. You can setup the model in Modflow/Mt3dms. Note that you wil have to follow the same rules of sensitivity analysis and calibration in finding the effective porosity. There should be literature available by USGS for these kind of tests.

Since you are from Asian Institute of Technology, there will be field hydrogeologist at your institute. They have done these kind of tests scores of time and are specialists too.