Final answer:
To calculate river discharge, the measurements needed are the river's cross-sectional area, average flow velocity, and a consistent unit of time, typically resulting in a discharge unit of cubic meters per second.
Step-by-step explanation:
To calculate the discharge of a river at a certain point, one must measure the river's cross-sectional area, and average flow velocity, and have a unit of time for which the discharge is being calculated. The cross-sectional area can be determined by measuring the width and depth of the river at regular intervals across the channel.
Average flow velocity is typically gathered using a flow meter, where measurements are taken at various depths and points across the river's cross-section. The unit of time chosen is typically seconds, to remain consistent with the commonly used discharge unit of cubic meters per second (m³/s). Discharge is then found by multiplying the cross-sectional area by the average flow velocity and is represented by the formula Q=A*v, where Q is discharge, A is area, and v is velocity.