[GS] When can you place Dams?

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acluewithout

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What are the rules for placing Dams?

I thought I understood them, but then every now and again I design some awesome IZ / Aqueduct / Dam Three City Production hub and... it all goes to crap.

Is the rule it must traverse two adjacent sides and only two adjacent sides of a hex?

So, if I have a hex numbered like this:-

3 /——\4
2|———|5
1 \——/ 6

Then a river running from 6 to 3 is valid? But 6 to 1, or looping around from 6 to 4 is not?

Advice welcome. Preferably with diagrams covering what is and is not acceptable.

(Dear @Sostratus, don’t let me down now...)

(You know, that search function could really use an option for highlighting locations particular districts can be built.)
 
Last edited:
Don't forget only 1 dam per river. I made that mistake yesterday thinking I could have 2 dams and 2 aqueducts adj to an IZ, but both dam sites were on one river. Sux because there was another river adjacent but I used up my spots for dams there with other districts (playing Japan). Wish you could remove districts if they are damaged or incomplete. Then again, if I didn't abandon most of my games in the medieval I'd also know the rules for late game mechanics better.
 
You can have all sorts of multiple river craziness, but sometimes this can get you in trouble because a hex that looks like it's got 2 sides from one river actually has multiple rivers. There are even civs where the river list has entries that are 1 letter apart.

The dam reservoir does have some kind of graphical restriction thing going with it. I cannot put my finger on it exactly, but if you have like a full loop around, sometimes the dam will not be allowed because the reservoir entry/exit would be messed up. It is exceedingly rare I come across this, though. Can you put up a screenshot?
 
Victoria said:
we all got it wrong.
Click to expand...
Hmm or did we....Lets look at this...
Here are 2 rivers, neither has a fork... but only one of the rivers is named
Spoiler :

upload_2020-4-4_21-42-15.png


So for Guangzhou, only 2 spots... the other 2 spots only have one side on the river and one is not valid as it has a resource on it.
Spoiler :

upload_2020-4-4_22-8-53.png


For Jiadong it seems to be ignoring the unnamed river completely.
EDIT: It turns out the right river tiles do not say there is a river there so it must be a bug.
Spoiler :

upload_2020-4-4_22-10-27.png


And here are 2 dams on the same river but on different floodplains. EDIT: in fact looking at the tile river names it turns out to be 2 rivers.
Spoiler :

upload_2020-4-4_22-17-2.png


Judging by this, only the source tile (dam hex) cannot have a resource. The target tile ('other side of the dam) can
Spoiler :

upload_2020-4-4_22-35-42.png


Now... if we re-read the help ... it is a touch ambiguous but we now know it means per floodplain of a river.
upload_2020-4-4_22-37-20.png

Can the target hex have only 1 side?... yes
Spoiler :

upload_2020-4-4_22-47-13.png


And you can have a target floodplain that is a different type (source plains, target desert here)
Spoiler :

upload_2020-4-4_23-2-48.png



... but then I find this and feel confused. the ySuggestions? .. and why can ellow X tile not be a source? ... 2 rivers?.. EDIT: Seems like 2 rivers, shown left.
Spoiler :

upload_2020-4-4_23-37-39.png

 
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Max files in last post so continue here

here Changsha builds a dam and Taiyuan still has options on the same floodplain
Spoiler :

upload_2020-4-4_23-58-11.png


Now if Changsha builds a dam on the other river ... it swaps
Spoiler :

upload_2020-4-5_0-5-2.png

Note the yellow x tile no longer is an option even though it could be on both rivers. Also not the target tile for the dam does not have to be in the city borders.
So the yellow x tile is either assigned to the left river or is not an option because it is the target of another dam...
upload_2020-4-5_0-6-29.png


Aaah, looks like that tile is assigned to the Wei river (left river) Which is why Taiyuan can no longer build a dam adjacent to the city (tile is also Wei river)
Spoiler :

upload_2020-4-5_0-13-20.png


AHA ... the red circle tile here is not a valid source tile because the tile is assiggned to the Wei river and while the yellow X hex side is on the wei river, the aqua X hex side is for the Murray river so it does not have 2 hex sides assigned to the same river.
Spoiler :

upload_2020-4-5_0-24-9.png


So some rules I guess
================
  1. The dam tile hex must have 2 river borders for the same river to be valid and it cannot have a resource on it.
  2. The dam tile hex must link to another hex (target hex) which is a floodplain of any type on the opposite side of the same river. The target tile can have a resource on it.
  3. Each tile on a floodplain is assigned to a specific river and all adjacent floodplain tiles assigned to the same river count as a floodplain for that river.
  4. Each river can only contain one dam. I have found no proof of otherwise)
  5. Each city can only build one dam
 
Last edited:
Victoria said:
Max files in last post so continue here

here Changsha builds a dam and Taiyuan still has options on the same floodplain

Now if Changsha builds a dam on the other river ... it swaps
Spoiler :

View attachment 550982
Note the yellow x tile no longer is an option even though it could be on both rivers. Also not the target tile for the dam does not have to be in the city borders.
So the yellow x tile is either assigned to the left river or is not an option because it is the target of another dam...
View attachment 550983

Aaah, looks like that tile is assigned to the Wei river (left river) Which is why Taiyuan can no longer build a dam adjacent to the city (tile is also Wei river)

AHA ... the red circle tile here is not a valid source tile because the tile is assiggned to the Wei river and while the yellow X hex side is on the wei river, the aqua X hex side is for the Murray river so it does not have 2 hex sides assigned to the same river.

So some rules I guess
================
The dam tile must have
... each tile on a floodplain is assigned to a specific river.
Where a floodplain is at the meeting of two rivers individual floodplain tiles are assigned to one floodplain or the other.
Because it is one single floodplain, only one dam is allowed per river on that floodplain
Click to expand...
After all that, all I can say is that the rules for placing dams are ridiculously complicated, nearly impossible to comprehend, and unbelievably frustrating for the player. Why must it be this way??
 
qadams said:
Why must it be this way??
Click to expand...
I just updated with 5 rules... not super complicated but I guess they just want to limit the number of dams in one area in some way and if I want to criticize it I need to come up with a simpler alternative. I am not sure I can.
All of my post pictures were a journey to discovery rather than a tutorial.

... and now I understand the rules I can do this
upload_2020-4-5_0-48-53.png
 
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@Victoria as I understand my experience most of the issues are caused by these river fork situations. The tile itself seems to be assigned to ONE of the rivers that touches it (probably the first one generated?) which you can deduce as you did, by hovering over the tile. But where rivers meet, the individual segments of river can be assigned to different rivers. You can end up with a tile touching 1 edge of river A, two edges of river B, and being assigned to A. So that even though it has 3 edges touching, as far as the dam is concerned it’s only got 1 side touching A and thus is invalid.

Its almost 100% this type of thing. When you get one strip of tiles with a floodplains on each side (a Tigris and Euphrates type deal) it can get really messy. Always, always, always, check the tile tooltip to see what river it’s attached to!!
 
@Sostratus @Victoria Thanks!

I’ll play around a bit more and see I can follow the examples! I think maybe I haven’t been paying attention to the “floodplains” requirement - I’d assumed any flat tile was okay, so long as the river requirements were met.
 
Perhaps the settler lens, or at least some lens, should show potential dam adjacency bonuses along rivers.
 
Victoria said:
Hmm or did we....Lets look at this...
Here are 2 rivers, neither has a fork... but only one of the rivers is named

So for Guangzhou, only 2 spots... the other 2 spots only have one side on the river and one is not valid as it has a resource on it.

For Jiadong it seems to be ignoring the unnamed river completely.
EDIT: It turns out the right river tiles do not say there is a river there so it must be a bug.

And here are 2 dams on the same river but on different floodplains. EDIT: in fact looking at the tile river names it turns out to be 2 rivers.

Judging by this, only the source tile (dam hex) cannot have a resource. The target tile ('other side of the dam) can

Now... if we re-read the help ... it is a touch ambiguous but we now know it means per floodplain of a river.
View attachment 550968
Can the target hex have only 1 side?... yes

And you can have a target floodplain that is a different type (source plains, target desert here)


... but then I find this and feel confused. the ySuggestions? .. and why can ellow X tile not be a source? ... 2 rivers?.. EDIT: Seems like 2 rivers, shown left.
Click to expand...

  1. Why can't Guangzhou build one hex north-east of the city center? It looks like it has at least 2 sides on the river. (unless it's two rivers with its sources hidden behind the city label)
  2. I don't think that there's anything like a "target hex" to be considered. That just overcomplicates things.
  3. Jiaodong should be able to build two dams (one for each river) if it wasn't for the bug.
  4. Best thing is just reading the tool tip to see which flood plain belongs to which river...
 
Victoria said:
Each river can only contain one dam. I have found no proof of otherwise)
Click to expand...

Uhm, you posted this pic with two dams on one river on separate floodplains:

upload_2020-4-4_22-17-2.png


I don't think I ever had a chance to test this. Most rivers are too short.
 
Victoria said:
  • The dam tile hex must have 2 river borders for the same river to be valid and it cannot have a resource on it.
  • The dam tile hex must link to another hex (target hex) which is a floodplain of any type on the opposite side of the same river. The target tile can have a resource on it.
  • Each tile on a floodplain is assigned to a specific river and all adjacent floodplain tiles assigned to the same river count as a floodplain for that river.
  • Each river can only contain one dam. I have found no proof of otherwise)
  • Each city can only build one dam
Click to expand...
1. Correct
2. Correct
3. Correct
4. As far as I remember, every "floodable area" can build a dam. One river can have multiple floodable areas divided by rough terrain.
5. I'm pretty certain I had options to build more than one dam. But these might've been captured cities.
 
Rivers are buggy.

I made a bug report about two Dams appearing on the same river, even though they're actually on different rivers. A Dam was built on a river other than the one specified in the tile's tooltip infobox. Also, in that example, building one Dam first prevented building the other Dam, but not if the other Dam was built first, which shouldn't happen.
Spoiler :
F9DCCBA12B9E0B22DE50157F17AEB7F8160C7AF8

I made another bug report a couple of days ago about rivers not having names. Are all rivers supposed to have names?

They need to fix it so that all rivers have names, and also that a Dam is built on the river specified in the tile's tooltip infobox, as neither of these things appear to currently be true.
 
Slightly related: it's annoying that you can only updrade one dam to hydroelectric if you have more than one dam per city. So if you can choose between cities it might be better to spread them (if that doesn't mess up adjacency bonus for an IZ of course).
 
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