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[jcochran]

I recently "energized" a patch of water to power a waterwheel without actually having the water flow and incurring the FPS hit caused by flowing water. But I made a simple mistake. My first reaction upon seeing it (just after committing and hitting the 'lever') was 'Oh shit! Flood recovery time'. followed a short while later by 'Why isn't my fortress flooding?'

In a nutshell, here's what I have


Z+0
##### 
##<##   Stairs leading up to aquifier
##+##
##+##
##+##
##+##
##+##
##X##    Floodgate.
##+##
   ...  Heading towards edge of embark with wall tile smoothed and carved into a fortress to allow water to escape.

Z+1 (Before & during energize)
##### 
##X##   Up/down stairs leading up to aquifier
##O##  Constructed wall to contain water
##+##
##+##
##+##
##+##
#####

Z+1 (After energize)
##### 
##X##   Up/down stairs leading up to aquifier
##O##  Constructed wall to contain water
##+##
##.##
##.##
##.##
#####


In a nutshell, I dug a tunnel that included the area where I wanted some 'flowing' water for my water wheel and had the tunnel go to the edge of the map where I smoothed and carved the tile to allow water to escape. Between the location where I was going to introduce water, I installed a flood gate and opened it. Once, that was done, I dug upwards 3 Z levels until I tapped into the bottom of the aquifier that was above my location. I then walled in the location where I tapped to keep the water under control and waited until the water flow reached the edge of the map and escaped. That based upon some posts in this forum and my own experience "energized" the passageway so that water within it would be considered 'flowing'. I then closed the floodgate.

After closing the floodgate, I then channeled into the tunnel from the Z level above it. Unfortunately, I forgot to have a 2nd flood gate upstream of the one I had installed and just closed. So I was left with an unrestricted path of water from my current location up to the aquifier a couple of Z levels above me. My understanding is that when I channeled into that tunnel of water, I should have immediately unleashed a flood into my fortress. Instead, I got a placid stretch of 7/7 water one Z level befow my channel and when I built my water wheel, it supplied power.

My conclusion... One of the following is true. Don't know which.....
1. Current beliefs on pressure are incorrect.
2. I somehow provoked a bug of some sort in 34.11. Most likely in some sort of optimization of fluid movement code.
3. Stairs permit the flow of water, but eliminate pressure.

[AutomataKittay]

I've seen comments that stairs seem to neutralize water pressure coming above it in older versions, I've not actually had any staircases in use for water in a while that's not been open on multiple levels.

Otherwise, it should've flooded up to equalize pressure, so I'm guessing it's either a bug or you hit a really niche pressurization situtation. Pressure works as understood otherwise.

[Crashmaster]

the tile of free water on the up/down stair on z+1 has no pressure because aquifers do not exert pressure. The water cannot find an open place on a lower level (z+0) to move to so it doesn't move.

just like on the the wiki

[jcochran]

I have to disagree there. The aquifier I tapped into is several Z levels above where I channeled for the water wheel. So I see a 7/7 water tile at the same level as the channel. Plus another 7/7 water tile a Z level higher, and finally one last 7/7 water tile at the point where I tapped into the aquifier. Even if the aquifier doesn't have any pressure, I have a column of water that's 2 Z levels above where I channeled.

Z+0 = Level where I have a tunnel leading to map edge for drainage. Tunnel blocked via flood gate. Has up stair leading to aquifier above.
Z+1 = Level where water wheel is. Additionally, connected to tunnel is up/down stair filled with 7/7 water.
Z+2 = Continuation of up/down stair. Also filled with 7/7 water.
Z+3 = Continuation of up/down stair. Impermeable stone layer directly below aquifier. Filled with 7/7 water.
Z+4 = Aquifier.

So even if an aquifier doesn't have pressure, that standing column of water (that's being filled from above by the aquifier) ought to pushing water into my fortress through the channel giving access to the water wheel. As I mentioned, the only thing I can think of is either a bug, or somehow the stairwell is eliminating pressure.

[WhimsyWink]

All of this is a little over my head ... but to achieve water flow over my wheel that reached into the aquifier I started a pump to output right at one end of the wheel drawing from a channel down tile ... wheel powered up and I stopped pumping ... wheel has been running ever since ... I have no sense of whether it is SUPPOSED to work this way ... I was 'spiff-balling' as we say in these parts ...

[jcochran]

As for power generation in dwarf fortress, you can do far worse than to read this thread.

http://www.bay12forums.com/smf/index.php?topic=99317.0

I've gotten into the habit of when I need power, I'll create as large as a pool as convenient, In many cases, the pool is far larger than what I need immediately, but since the only cost is a bit of digging, it's no big deal. Now, I'll initially use only as many water wheels as needed, but if I need more power later, it's easy to add more wheels, but a lot harder to increase the size of my pool. Usual method of pool generation is as follows.

1. Dig out pool area to include smoothed and carved fortification to provide drainage. Pool has 2 floodgates. One at the entrance, one at exit. Also pool is entirely confined to a single level without any openings and such for water wheels (e.g. It's safe to have pressurized water in it. No flood danger).

2. Now close output flood and open input flood gates and turn on the water. Allow the pool to fill.

3. While keeping input flood gate open, open the output gate and allow the water to drain off the edge of the map.

4. Close the output gate again and let the pool fill to 7/7.

5. Close the input gate.

6. Disassemble the levers controlling the flood gates (I lost a fort once because I foolishly thought that the levers might come in handy one day.)

Now when ever you need an extra 90 power, just channel a nice 1x3 section about into the pool, mount a water wheel and let it spin.

I've gotten the water to fill my pools by tapping into rivers, aquifers, oceans. What ever is available at the time.

Haven't tried to energize any pools by using the caverns. My own thought on the matter is that pouring the water into the cavern lakes is likely to 'break' the continuous flow of water that the program seems to notice to flag a section of water as 'flowing'.

[Crashmaster]

Ok, then I will give an example of a different pressure mechanism that might lead to an answer.

An old fort. River fed 10x10x10 cisten. Its lowest output would not rise water up a verticle shaft the expected amount. When the cistern fill gate is closed isolating it fom the river tiles the water balanced to the correct level as predicted by the wiki.

Theory is that water ways linked to a natural water source or drain (and aquifer is both) have a buggy affect on the pressure in that system.

If you could shut off the connection from the aquifer I would suspect that now the lower channel on z+0 would overfill from the water still in the shaft leading down from the aquifer.

I'll throw a guess out there that this has something to do with implementing natural waterfalls so they don't flood the surrounding terrain.

[jcochran]

Perhaps. But in any case, can't test that theory with this fort (don't have the required floodgate). However, an earlier experience (which is the reason why I now disassemble the control levers after energizing a pool of water) would seem to indicate otherwise. To wit...

I constructed a pool and used as the source of water the ocean on the edge of the map. The pool was about 5 Z levels below the ocean. Ended up with both the input and output floodgates closed, channeled for the waterwheel, built it and hooked it up to the items it needed to power. Then I decided to play around a bit with the levers.

First, I opened the output floodgate to see how fast (or slow) the water drained until the waterwheel no longer functioned.
Second, I opened the input floodgate to see how high the water would get with the drain active.
After I got bored, I then decided to set things back to normal and closed the output floodgate to let the pool refill.
That was my mistake......
The pool filled quite rapidly (during my initial fill of the pool before I started playing around with it and before I channeled it for the waterwheel, it took about 5 ticks to completely fill. And that was for a pool measuring 5x9 tiles. Yes, the water was definitely under pressure). And as soon as it filled, water started pouring up around the waterwheel (thereby teaching me that water wheels don't make water tight connections with the Z level below....).
I immediately attempted to close the input gate. But unfortunately, the lever was in the room next to the waterwheel. And the water was flowing fast enough from the waterwheel to the room to the exit that the dwarves couldn't get to the lever to pull it. Definitely learned a lesson there so I now get rid of that lever as soon as things are set up. Both to keep me from temptation and to keep a tantrumming dwarf from pulling it too. And since that eliminates the ability to refill the pool, I get rid of the lever to drain it as well.

But I mention this because it provides a counter example. The ocean is a 'natural' source of water. And the drain that I was using was an aquifier several Z levels below that pool in the story. Also a natural drain.

[Crashmaster]

Someds are kicking in harder so i dont think i understood how the system operated. How high it got. When the system was operated second with both floodgates open....

Skip understanding and ill just say that tapping any water source with a large surface area on the top level will cause very fast water teleportation as each tile of water on the top layer will teleport to the nearest lower available empty space. Kind of like super surface pressure.

With the drain open each water tile could teleport right off the map at a very high speed. I would assume that drain channel was full of 7/7 all the way to the edge. Once the drain gate closed the lowest level is already full so the water tiles start to teleport to the nearest reachable spot on the next levl up.

Very clumsy explaij right now but may be some sense..... 

[AutomataKittay]

Someds are kicking in harder so i dont think i understood how the system operated. How high it got. When the system was operated second with both floodgates open....

Skip understanding and ill just say that tapping any water source with a large surface area on the top level will cause very fast water teleportation as each tile of water on the top layer will teleport to the nearest lower available empty space. Kind of like super surface pressure.

With the drain open each water tile could teleport right off the map at a very high speed. I would assume that drain channel was full of 7/7 all the way to the edge. Once the drain gate closed the lowest level is already full so the water tiles start to teleport to the nearest reachable spot on the next levl up.

Very clumsy explaij right now but may be some sense.....

The problem's there're a few z's of water in staircase that's being filled by aquifier above, and the water aren't flooding through the hole on lowest floor. There're no water coming UP.

I still suspect it might be staircase neutralizing pressure that I've heard a few times in older version.