How does cross-sectional area affects stream velocity?

The cross-sectional area of a stream influences its velocity due to the principle of continuity, which states that the flow rate must remain constant along a streamline. When the cross-sectional area decreases, the velocity of the water increases to maintain the same flow rate, as seen in narrower sections of a stream. Conversely, when the cross-sectional area increases, the velocity decreases. This relationship explains why streams often flow faster in narrow channels and slower in wider areas.