Throughout Disneyland there are clear water attractions such as Small World, Splash Mountain and the Pirates of the Caribbean with their own body of water. Then there are the dark water attractions which are all connected together. The clear water attractions are isolated but the dark water attractions are connected. This stream is attached to the moat that goes around Sleeping Beauty's Castle to the left but to the right it's tethered into the river from the Jungle Cruise.
Having the water flowing adds so much background sound and energy which emotionally makes us feel like we are someplace tropical.
One of the subtle details that makes Adventureland feel tropical is this stream right along the edge of the Indiana Jones queue and the beginning of the treehouse. This stream is creating the sound of water that makes us think that we're someplace in the wilderness. This water is connected to the rivers of the Jungle Cruise. But aside from the adventurous water noise, all of the plant life, the rock sculptures, the noise of the water are pieces of the puzzle that feel distant from one another when really they're quite close.
At the head of the waterfall or the pump, that helps recirculate the water to all the different destinations, so the water system can fully irrigate and self-regulate not go stagnant.
Growing up in Los Angeles in the 70s/80s we visited Disneyland on a regular basis and often after school, before "Annual Passes".