The total capital expenditure chargeable to a project shall be allocated between the three main objects, namely, irrigation, power and flood control as follows, namely:---
         (1) expenditure solely attributable to any of these objects, including a proportionate share of overhead and general charges, shall be charged to that object, and
         (2) expenditure common to two or more of the said objects, including a proportionate share of overhead and general charges, shall be allocated to each of such objects in proportion to the expenditure which, according to the estimates of the Corporation, would have been incurred in constructing a separate structure solely for that object, less any amount determined under clause (1) in respect of that object.