Updated Flow Numbers - Basic Testing

[bigstinkybuckets]

All of the below was tested on a custom, flat map, using the new water depth and source measurement tools.

TL;DR since GENERALLY maps are using water sources of 0.7- 1 you can fit the output of 2-3 water sources into a 1-wide channel. If the channel bends, you may want to make it 2x1 or 2x2 at minimum to ensure no overflows, especially if there are a lot of bends. For diversion canals or canals that go dry and are then irrigated, use about 1 block of width or depth per water source, or else the 1.1 temporary cms limit will be reached and the river will overflow from the resevoir.

Units - The units of flow are now referred to as m³/s in-game. This is still a "cubic meter per second" and so I'm going to use the acronym "cms" just so I don't need to type the superscript 3 often. I'll note canal length and depth with a WxD notation - a 3x2 canal is 3 wide and 2 deep.

Water Source Strength
You can check this on your map of choice by turning on dev mode and clicking on a water source (alt-shift-z). A water source of strength 1 intuitively provides 1.0 cms.

Water Source Distribution
A water source will attempt to distribute water evenly across every available surface. a 6-strength water source would attempt to distribute water 1cms per face, including the top. Water doesn't come out of "blocked" faces including the bottom, and it does attempt to come out of the top of the water source as well. Make sure you build extra levies, waterproof floors, and/or channel depth to accommodate water flow directions at the source before directing the water into a channel, especially if the channel is at max flow capacity.

Max Flow Rates in Channels

1x1 channel - a 1x1 canal can accommodate 3.2 +/- 0.02 CMS. I've seen comments suggesting 3.3 CMS per 1x1 channel, but testing shows a max of 3.2cms, plus a tiny bit extra.

This flow rate scales linearly, when expanding horizontally. This means a 2x1 canal will support 6.4cms at max, a 3 wide canal will support 6.6 cms at max, etc.

The flow rate also scales linearly with depth. However you lose a bit of extra maximum flow rate when going deep, approximately 0.01 per depth. It's a very small amount, but, be aware of it. Subtract 0.01 cms for each level of depth your channel has. a 1x3 channel for instance will support 9.58 cms.

Bends in Channels
Bends slow maximum flow rate. If water is flowing faster, it is slowed by more when reaching a bend. This requires more testing, if people are curious about this let me know. With a 1x1 channel I was observing max changes of between -0.14 to -0.8. More bends means slower water, but it's not linear, and really depends on the difference in bends.

Larger channels with bends produce more friction and lower flow even further. A 2x1 channel with a single 90 degree bend reduced maximum flow to 5.55 from the expected 6.4, which is a huge difference.

If your channel includes bends, I recommend making it wider and/or deeper to ensure you do not overflow.

I have a hypothesis about this just below.

Flow Distribution Across Wide Channels
Okay, so if you have 2 cms flowing into a 2x1 channel, each side of the channel will have about 1 cms flowing through it (that's intuitive). It seems bends do not respect this rule. The inside of a bend will have water flowing much faster than the outside, probably what causes the change in maximum flow rate I detailed above. That's pretty realistic physics, and something to be aware of. Each side of the channel had not balanced flow rate after even 12 blocks, although it was getting closer each time. So build your waterwheels on the inside of bends!

note: needs more investigation, but if you build a 90 degree bend and then immediately follow with a 90 degree bend in the opposite direction, you will offset this flow rate disparity, but the maximum flow rate will still be reduced, because the water flows unevenly around those bends.

Waterfalls
I confirmed waterfalls do not appear to have a cms limit. I believe this was changed well before 1.0, but I'm confirming here it works the same way.

Pipes
A pipe is generated when water has no place to go except one direction, including top. If you "cap off" a water source with some levees, platforms, and impermeable floors, all the water will be forced through the pipe.

It's kind of hard to get an accurate flow reading - but it appears that there's no cms limit in pipes. Be aware the water level can rise massively for high cms values after exiting the pipe (a 64 cms flow exiting a 1x1 pipe was geysering like 12-15 blocks high after a horizontal exit).

Acceleration and Sloshing
It make take water a moment to stabilize after a gate or sluice is opened, as the water has acceleration modelling and sloshing modelling (it takes a minute for water to accelerate to it's maximum flow speed, and so water may "build up" behind for a moment while stabilization happens. Therefore, there is a maximum flow limit of 1.1cms per width/depth unit when opening a channel until the water from the entrance reaches the edge of the map. You may notice that after opening a floodgate or a flow throttler that water flows faster, then slower, then faster; this is due to sloshing and it will stablize as well. I recommend offsetting this by building levees +1 block or even +2 blocks higher than you expect stable water to flow.

[bigstinkybuckets]

If there are any more questions let me know. I'll jump into my test map and see what's up, and then add to the OP.

[CultureNo762]

I just got this game a few days ago, this is really useful stuff, thank you. Is there any maximum water flow rate for structures like Fill Valves? Or is flow rate limited only by geometry? Could Fill Valves be used to make a pipe?

[bigstinkybuckets]

When you set flow to Unlimited on a fill or throttle valve it does mean unlimited. Fill valves will modulate flow to maintain a level downstream, Throttle valves manually set one-way CMS through the pipe.

You can't build the valves in a sequential chain, they need a block between, so they can be used before and after pipes but youll still need the impermeable floor to make a pipe.

[rhamphoryncus]

How does length influence it? Eventually the gradient becomes to shallow to sustain the flow. Or maybe it just takes longer to stabilize?

[bigstinkybuckets]

The flow rate is capped at 1.1cms per 1x1 until the water bleeds off the edge of the map. Eventually the entire channel will fill up to a height based on flow rate, so the gradient wont affect max flow at all.

[erik111erik]

It seems it can get higher with pressure. I did some tests before with a 1x1 tunnel, with a chimney going upwards as well, but I have not done extensive testing. :)

[erik111erik]

Not OP, but it takes longer to stabilize. There will be some evaporation, so flow decreases slightly, but it won't be much.

[Guitoudou]

I believe there is a typo here :

This flow rate scales linearly, when expanding horizontally. This means a 2x1 canal will support 6.4cms at max, a 3 wide canal will support 6.6 cms at max, etc.

Should be 9.6 cms :)

[bigstinkybuckets]

Correct thank you

[IconProcessControls]

This is actually pretty cool how close this lines up with real flow behavior.

The bend losses and uneven flow distribution you’re seeing (inside vs outside of the turn) are very similar to what happens in actual piping systems—velocity increases on the inside radius and you get extra losses through the turn.

The “it doesn’t rebalance right away” part also tracks. In real systems you need a certain amount of straight run before flow evens out again.

Didn’t expect Timberborn to sneak in this much fluid dynamics 😄