wide expanse, abundance, vigorous
浩 centers on vastness and fullness: a wide expanse, great abundance, or vigorous energy. The meanings all point to something large, overflowing, or powerful in scale.
浩 combines 氵 (water) with 告, which likely contributes the sound. The water radical suggests a vast expanse of water, fitting the meanings of wide expanse and abundance.
Water (氵) spreading out in all directions, as if announcing (告) its vastness. Imagine a flood that covers everything, creating a wide expanse of vigorous, abundant water.
For コウ, picture a huge, wide ocean (浩) where a single koi (コイ) fish swims, but the ocean is so vast it's like a 'ko' sound echoing: koi -> コウ, emphasizing the expanse.