port, harbor
湊 centers on a place where things gather, especially watercraft: a port or harbor. The gathering sense extends naturally to the idea of people or things coming together.
湊 combines 氵 (water) with 奏, which likely contributes the sound and the idea of gathering or converging. The character suggests water gathering at a port.
Water 氵 meets the gathering component 奏: picture boats and goods converging at a busy harbor.
For ソウ, imagine a harbor so crowded that boats are packed like a tight row: sew -> ソウ, as if the boats are sewn together at the port.
end of spring