Pond Size Calculation for Farm Irrigation

I do research ​in the field of ​water use in ​agricultural ​irrigation and ​I want to make ​a sustainable ​irrigation ​source for ​farmers ​in India.​  ​

What size of ​the pond ​would ​be big ​enough for ​irrigation ​supply of the 2.​5 acres ​area for 4 ​months for ​crops ​which don't ​require too ​much water?​  ​

The idea is ​that the pond ​is ​lined with ​a ​polyethene ​sheet ​and ​filled ​during the ​rainy season by ​rainwater ​harvesting.​  ​

How can I make ​these ​calculations? ​Are there any ​such formulas?​  ​

Which factors ​influence ​the equation ​the most and ​which are ​negligible?​  ​

Which ​depth should ​the pond be? Is ​the depth of 1 ​m okay or ​should it be ​deeper with a ​smaller surface ​to reduce ​evaporation?