Water flows more quickly when falling under pressure to a lower z-level. This leads many players to assume that an increased difference in altitude will further increase the speed of flow. My own experience with water, however, suggested that relative altitude would determine only the level to which pressurized water would rise, not the speed at which it would travel.
I performed an experiment in which a two-level-high and a five-level-high cistern containing equivalent volumes of water were drained simultaneously.
The taller cistern actually drained more slowly than the shorter one, showing that an increased altitude difference does not cause an increase in flow rate.
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Submitted by: Doppel - 2009-08-23
Your floodgates and towers aren't located in the same position relative to the cisterns. I'm guessing that both fill at the same speed when everything is lined up correctly.
Would be interesting to see if this experiment is repeated with bigger extremes, thinking a 20 z level high tower against a 2 z level high one.
Submitted by: Quietust - 2009-08-23
It actually makes sense - each tile of water can only push down once per frame (and it usually takes 8 frames or so for an entire Z-level to move downward - single-step through falling water to see the pattern), so a larger surface area will result in greater pressure for a shorter duration.
Submitted by: Gugunja - 2009-08-23
To be sure, I conducted an experiment with 2 1x1 columns of water. One was 5 z-levels high and the other was 12 z-levels high with the bottoms being on the same level, and the original water source being the same (a stagnant pond on the surface. I watched how long it took each of them to fill a 1x4 space on the bottom level once floodgates were removed (simultaneously). There was no significant difference.
Submitted by: Kanddak - 2009-08-26
First of all I need to link this thread: Hydrodynamics Education
This is most of my current working theory of water.
So, Doppel: what's your theory of how water moves that would explain why the alignment would make a difference? My prediction: You can't produce any alignment of the two cisterns that will put the 5x5 tower ahead. I'll eagerly await your own video to prove me wrong.
Gugunja: Yes, I would expect two 1x1 towers to go at about the same speed. You also filled a very small space that would make it hard to observe a difference.
Submitted by: Kami - 2009-10-23
Toad has explained somewhere how water in dwarf fortress workes. There does not exist any kind of pressure like in the real world. Pressure (if you can call it like that) meaning the speed water moves form a full tile to an empty tile does not depend on the height but on the area of the water surface.