Q$-6.$ Find the average drainable porosity $($in percentage$)$ of the soil in a field condition as described here: In a groundwater drainage network, $15$ lateral drains laid at a spacing of $35m$ and each $135m$ long, join a collector drain. The average discharge at the outlet of the collector drain was $12$ litre$-$per$-$second when the water table dropped from surface to $50cm$ below surface in $2\mathrm{.}5$ days.