My friend in Theni, Tamil Nadu has a 60 acre farm, of which 50 is laid out with an orchard of pomegrante, lime, sapota and trees like teak, etc. There are approximately about 3000 trees on this 50 acres. He has installed drip irrigation.

If he were to discontinue reliance on groundwater which is now at about 400 feet, what size and depth of a pond would he have to construct to ensure that water for 9 months a year for all trees is available through rainwater harvesting?

My rough scratchings indicate that about 18,000 kilolitres of water is required. This would mean a pond of about 50m x 120m with a depth of 3m. Am I correct?

And is it feasible to collect and store rainwater in this way for irrigation?

Pls comment and reply.