lake in Yunnan
洱 is a specific geographical name referring to a lake in Yunnan, China. Its meaning is tied to that place name rather than a general concept.
洱 combines 氵 (water) with 耳, likely as a phono-semantic compound used for the name of a lake. The exact historical development is uncertain.
The water radical 氵 beside an ear 耳 suggests listening to the water of a specific lake. Picture the ear hearing the gentle waves of Lake Erhai in Yunnan.
For ジ, imagine a giant ear listening to the lake, and the sound it hears is a soft 'ji' like the gentle lapping of water: ji -> ジ.