Parallel drainage pattern. A parallel drainage system is a pattern of rivers caused by steep slopes with some relief. Because of the steep slopes, the streams are swift and straight, with very few tributaries, and all flow in the same direction.
1 In Creative, the player can use spawn eggs to spawn most mobs. 2  When mobs are spawned this way, all normal spawning requirements, such as light level and block type, are ignored. 3  Any entity can be spawned using the /summon command.
Slimes spawn 1/10 times than normal hostile mobs. Make sure you have the area well lit and the area around it well lit also to decrease the chances of hostile mobs spawning. Plus you have to get a certain radius so mobs can spawn. I had the same trouble too with my slime chunk, you just have to wait a while.