I think the development ...

I think the development objective should be 'improved irrigation efficiency."  Consumptive use can be determined from a 10-day calculation of ET from the local climate data and crop types.  Note I say types because the large area has a low probability of being monocropped.  Irrigation efficiency is the ratio of net water applied.  The net water applied is the total water input minus seepage from canals and percolation losses into the soil from the canal/pipe to the plant.  In most irrigation systems main canals are generally lined and their unit area seepage loss can be estimated from the type of lining.  If the canal is instead a piped system, then there should be no losses. Similarly if the irrgation application system is piped (e.g. trickle) the area of soil losses will be from percolation losses around the plant only.