Hydraulics of the sharp-crested weir is investigated in order to obtain the base data for flood control planning of the rivers with weir(s). Relationship between the discharge and the upstream head has been obtained based on the momentum theorem, then the formulas for these two hydraulic quantities have been derived. In forming the momentum theorem, results of the previous experimental studies on the pressure distribution on the upstream surface of the weir and in the flow section where the lower nap becomes highest immediately behind the weir crest have been reflected. The obtained formulas are much more rational hydraulically and showed better agreement with experimental data than the previous ones in the upstream head range greater than weir height which is necessary in the application to the flood management planning.

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