Derive equtSaturated hydraulic conductivity Ks measured using a falling$-$head permeameter, Ks $=$ d$^2/$D$^2*$L$/$t$*$LN$($h$0/$h$),$ where d is the diameter of the small water tower, D is the diameter of the soil sample, L is the length of the soil sample, h$0$ is the initial water pressure head in the water tower above the higher end of the sample $($measured at time t $=0),$ h is the second water pressure head in the water tower measured at a time t $>0$