Can two spells with AOEs intersect each other?

Question

If my Triton character casts Wall of Water and my friend who is a Warlock casts Hunger of Hadar, can both of these spells intersect one another? My DM does not know to how to respond to this question. Both spell descriptions say

centered at a point you can see within range

I was thinking the warlock could cast the wall at some place then I cast my wall at a point next to the wall so they both intersect. Would that work? Also what about both walls being casted at the same point? Such as the warlock holding an action to cast it on the tree, then when I cast my wall at the same tree both of our spells would come out at the same time at the same area. Can this work?

Answer 1

Different spells can have intersecting areas.

There is no rule preventing different spells from having intersecting areas of effect. They may be some edge cases where the spells themselves prevent the areas from overlapping, but with the example you give, wall of water and hunger of Hadar, these spells can have intersecting areas.

For reference, the rule about overlapping spell effects explicitly states that the effects of different spells add together. From the section "Combining Magical Effects":

The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don't combine, however. Instead, the most potent effect--such as the highest bonus--from those castings applies while their durations overlap, or the most recent effect applies if the castings are equally potent and their durations overlap.

Answer 2

There's no rule against overlapping or intersecting areas of effect

Zones can overlap, and the rules for both apply. Generally the same spell can't affect you twice, so overlapping two castings of the same spell is a bit pointless, but with two casters throwing out spell effects that create zones on the board, there's no general rule that would prevent it from working.

That said, visibility can be a definite concern. In the case you mentioned, the hunger of Hadar zone is magically dark, so you can't target a point inside it with another spell that requires you to see the point you're aiming at. That said, as long as your target point is outside the hunger zone, the area the spell creates can extend into the darkness -- you are not required to see the entire spell area (unless the spell specifically says you are).

Wall of water says, "You create a wall of water on the ground at a point you can see within range. You can make the wall up to 30 feet long, 10 feet high, and 1 foot thick." (A ring shape is also available.) Like wall of fire, it doesn't say how the wall is shaped or where the 'point' is with relation to the wall, so I'll refer you to a few previous questions that discuss those two issues with regard to wall of fire:

What are the permitted shapes of a wall of fire?

Casting wall of fire in a T-shaped corridor

The second one there is really the important one in this case. Note that there is a slight difference in that wall of fire doesn't require you to see the target point. However, based on those answers, presumably the wall of water is a straight line, and the point of origin just needs to be somewhere along the line, but there's enough ambiguity there that your DM could certainly decide to rule otherwise.