“Accumulated overdraft” means the aggregate amount, as determined from time to time by the board of directors of the replenishment district, by which the quantity of ground water removed by any natural or artificial means from the ground water supplies within such replenishment district during all preceding water years shall have exceeded the quantity of nonsaline water replaced therein by the replenishment of such ground water supplies in such water years by any natural or artificial means, the respective determination to be based upon reports, records, and other data or evidence found by such board of directors to be adequate for the purpose of making such determination.