To examine the measuring accuracy for river discharge with floats, flood discharges obtained with float and ADCP measurements have been compared. Since the ADCP can measure vertical velocity distributions and water depth simultaneously, it may be one of accurate discharge measurements under various flow conditions except high flow conditions (e. g., u>3m/s). We also try to improve the accuracy of the float measurement with special attention to evaluations of lateral and vertical velocity distributions. The observed results indicate that the measured discharges obtained with floats are relatively larger than those with the ADCPs. The modifications of the lateral and vertical velocity profiles presented here may improve appreciably the measuring accuracy for flood discharge with floats.