PDA

View Full Version : DM Help What Happens To Brevoy If Lake Reykal Is Drained?



Wasum
2020-11-27, 08:48 AM
Hello everybody!

In my Pathfinder campaign beneath Lake Reykal there was an enormous system of tunnels and caves which completely collapsed after my players fought some Neothelids there and this caused the lake to get drained completely.

What are the consequences for the nation of Brevoy? Im interessted in the obvious ones as well as in some minor consequences causing interesting alterations to the surrounding area. And it doesnt have to be setting specific of course - think of the biggest lake within a country that hosts some of the biggest cities as well as the capital gets drained.

https://static.wikia.nocookie.net/pathfinderkingmaker/images/8/8a/Brevoy3-0-0.jpg/revision/latest?cb=20180917153324

I really appreciate your ideas, thanks in advance!

GeoffWatson
2020-11-28, 06:06 PM
There would be famine and other shortages in the capital.

In pre-modern times, water transport was much cheaper than land transport - eg Rome would ship in most of it's food from Egypt, as it was cheaper to sail across the Med than to cart it from other parts of Italy.

The capital would have farms nearby, but would that be enough?

Faily
2020-11-28, 07:03 PM
Without knowing which direction the rivers run, I'm going to make an assumption that Grey River, East Sellen River (northeast), and Stetven River flow into the lake, and that East Sellen River (south) runs out of the lake.


Immediate effect is the death of all fish and aquatic flora and fauna in Lake Reykal. This will massively impact the life around the lake, such as towns, villages, and farms, as well as wildlife. Thanks to the rivers running into the lake, it won't mean the death of fauna around the lake as most animals including water-birds will probably move away from the lake and to the rivers (or simply leave the area), but that will have deep effects on the ecosystem as well as the survival of the people there who are less likely to just up and leave like animals do.
Flora around the lake will most likely suffer, a lot of it die out.
Thanks to the rivers, there is still running freshwater, but for those who are not close to that vicinity many wells and freshwater springs tied to the lake will probably dry out when the lake did, causing trouble for crops, farm animals, and people who do not leave near the still-functioning rivers.
River-trade and transport will stop. And this one is a big deal, as we can tell from medieval maps and old cities that people would always flock towards rivers and waters not only because of access to freshwater but because it made transportation so much easier. Those using riverboats to move their trade will have that eliminated until the problem is solved, as GeoffWatson mentioned, but this also affects workers. Lumber is something that also has relied a lot on waterways for their work, as its much easier to send logs downstream than to haul them across land. Not to mention all the water-powered industries, that lumber is involved in (water-powered saws), as well as mills, and forges.

RifleAvenger
2020-11-28, 08:20 PM
I sort of question how the local water table allows for there to be rivers flowing to and from the lake, yet the lake itself could be completely drained?

That would essentially require the entire local water system to be lying atop an impermeable unit, with the topography such that the lakes and rivers filled the low points in the topography above that unit. Breaking this unit then results in the water being able to rapidly return to the actual water table far below.

Suffice to say, the geology of the area would need to be pretty contrived for this to occur. I suppose the artificial tunnels could have been built into an impermeable "capsule," but in that case their collapse and flooding would only drop the water table somewhat, not drain the entire lake.

Of course, the water table is the bane of many popular things in D&D and its children, such as the Underdark.

Ajustusdaniel
2020-11-30, 02:54 PM
One: Immediate massive economic collapse. Several industries are just outright gone, as are fish as a food source. A lot of people are going to be wondering where their next meal is coming from. Historically speaking, keeping prearranged food exports going in a situation like this is a great way to start a riot.

Two: This being a high fantasy setting, we can't rule out the possibility that the massive die-off of aquatic fauna and flora results in some sort of Spontaneous Necromantic Event (my new garage band name) and some sort of horrible Composite Fish Ghost (our first album) starts swimming through town.

Three: Where's all that water going now? Presumably you've opened up a hole into some sort of tunnel system connected to the underdark- a lot of that's flooded, and we can't rule out the possiblity of various underdark critters and communities fleeing to the surface through other exits after displacement by the flood.

Friv
2020-11-30, 06:05 PM
I sort of question how the local water table allows for there to be rivers flowing to and from the lake, yet the lake itself could be completely drained?

That would essentially require the entire local water system to be lying atop an impermeable unit, with the topography such that the lakes and rivers filled the low points in the topography above that unit. Breaking this unit then results in the water being able to rapidly return to the actual water table far below.

Suffice to say, the geology of the area would need to be pretty contrived for this to occur. I suppose the artificial tunnels could have been built into an impermeable "capsule," but in that case their collapse and flooding would only drop the water table somewhat, not drain the entire lake.

Of course, the water table is the bane of many popular things in D&D and its children, such as the Underdark.

My guess is that you're looking at somewhere like the Canadian Shield - a massive area of heavy rock, with layers of soil on top of it and poor hydrological drainage. There was probably a small amount of leaking into the caves below, but only in minute quantities which allowed the lake to continue to exist. Meanwhile, the tunnels kept growing and growing, until it didn't take much for the lake to break through into them, resulting in the collapse.

As time goes on, each layer of those tunnels is going to fill up again and the lake will return, although maybe not to the same height as before. You could end up with a very large, very shallow lake over the area. Other than that, I second Failey's assumptions about which way the rivers are running, and thus what the result will be; a huge problem for trade and commerce, a local catastrophe for fishing villages around the lake and anyone depending on trade for their livelihood, but not a massive famine; most of the greener farmland appears to be farther north anyway.

New Stetven is going to be in so much trouble, because it looks like they're the only major settlement sitting where the water comes out of the lake, so they won't have water, their farmlands are going to be in trouble, and if they're a large city on the mouth of a river coming out of a lake they're a huge trade route.

I notice the area to the south is listed as "Stolen Lands"; is that an allied nation, an enemy nation, or a mostly wilderness-area? There could be trouble from that direction, if the river is a major source of their own crops.

The one thing that might happen is a serious lumber shortage across the kingdom; it looks like most lumber was probably shipped by river before, and that's going to necessitate either an overland leg or a new route.

Clistenes
2020-11-30, 06:18 PM
Couldn't they try to compensate by building a dam to block the East Sellen River next to New Stetven? That way the lake loses less water and may keep existing... They could even build the dam near the sourthern frontier so that peasants across the river could keep taking water from the river (now a long reservoir rather than a true river...).

Another option would be to dam the Gray River, Stetven River and East Sellen River so they don't pour their waters into the lake, creating long reservoirs that would compensate somehow for the loss of the lake. They would loss some farming land that way, but they could compensate by farming the bottom of the former lake...

Alcore
2020-11-30, 06:38 PM
I notice the area to the south is listed as "Stolen Lands"; is that an allied nation, an enemy nation, or a mostly wilderness-area? There could be trouble from that direction, if the river is a major source of their own crops.

The one thing that might happen is a serious lumber shortage across the kingdom; it looks like most lumber was probably shipped by river before, and that's going to necessitate either an overland leg or a new route.
The Stolen Lands is where the Kingmaker Adventure Path takes place. The area directly south (and is fed by said drained lake) is called "The Green Belt" and would be* the most ideal place for farmers.


* As the name "Stolen Lands" suggests the land is currently distributed. No large faction can claim it due to interference from one another and smaller powers lack the power to maintain a foothold. The River Kingdoms to the south west provide no shortage of bandits, monsters and wannabee kings to tople over anything placed there not back with armies.

If the AP has not occured there than the bandit known as the Stag Lord rules. He is drowning himself into a tankard so even without four heroes the land is overdue for regime change. If the heroes arrive then a budling kingdom is down there. The drain on the lake won't hurt too bad; there are other rivers and lakes that they get water from. The Stolen Lands is technically part of the River Kingdoms and the name is not for show.

If the big bad of the AP wins? Several thousand square miles is reduced to desert that nothing can grow on... the soul of the land (and anything on it) spiriited away to The First World. Kinda like Barovia in Curse of Strahd

Alcore
2020-11-30, 06:42 PM
the biggest threat from the Stolen Lands is a kingdom to the south west of the lake. A River Kingdom players may have or may not have taken over. The warlord there would be happy to add more to his failing kingdom.

Duff
2020-11-30, 07:16 PM
The dried out lake bed will make for some amazing dust storms. If it goes like the Aral sea in Kazakhstan, the lakebed and dust will be toxic. So blowing dust could make the surrounding area a bit nightmarish. Cities where everyone wants to go, all the wealth is gone, everyone who's able to travel reasonably easily is gone and desperate people sell whatever they can to buy the food that people are willing to bring.
It could get a bit apocalyptic

TheStranger
2020-11-30, 07:26 PM
As has been noted, widespread famine and economic disruption would probably result. Fisheries in the lake are likely to be a major food source, and most goods (including food) in the nation are probably moved on the lake. Which makes this immediately the most pressing concern for Brevoy - this is the sort of thing that collapses civilizations. The solution, if at all possible, is to refill the lake.

Most likely, you have the lake draining via a relatively narrow breach through solid rock, although the force of water will tend to enlarge the initial breach. It's possible that a few high-level casters spamming wall of stone could just go underwater and repair the breach before the lake even finished draining, although it would take more than a few ranks in Knowledge: Engineering to add stone in a way that doesn't result in it immediately eroding away. Or you can wait for the lake to drain, temporarily dam/divert the major inlets so that the breach is mostly dry, and repair at your leisure. It's a pretty monumental engineering challenge, but far from insurmountable given that losing the lake represents an existential threat to the nation.

If it's impossible for some reason to block the breach and refill the lake, the next best thing is to dig canals in the lake bed connecting all the major cities. Divert the major inlets to fill the canals and flow out at the natural outlet. That would allow trade to resume, although you'd lose the fisheries. In that case, the nation probably survives, but is diminished somewhat.

Of course, both of those solutions require unfettered access to the lakebed. If Brevoy has an enemy that can contest control of the lakebed, that could make any large-scale mundane engineering pretty much impossible (though the high-level casters could probably still cast wall of stone just fine). This is certainly a golden opportunity for any internal or external forces to kick Brevoy while it's down, attempt a coup, or just generally cause problems.

Alcore
2020-11-30, 07:32 PM
My answer was so tiny, so incomplete.


the map that is provided in the first post is technically all part of one single kingdom. This kingdom was eventually unified by a single conqueror but it's still not quite a united kingdom in a sense that they don't want to leave. Then you have all of its neighbors to take into account two of which we have labeled on the map.


week one
In the first couple days a number of things will happen. Most aquatic creatures in the underdark are not something most surface aquatic creatures will want to face. so any aquatic creature with a decent land speed capable of thought is going to head up en mass to where all the humans are. Unprecedented levels of cooperation might happen over time. They might not become an army but armies might be needed to stim the flow.

Then you have the creatures of the underdark and the dwarves in the nearby mountains are going to get hit really really hard. And that mountain's name I cannot pronounce is the one to the northwest. They are going to be hit hard by just about anything wanting to get up to the surface. unless otherwise stated that is the only location to get out from the underdark. Being proper dwarves they're mostly dependent upon the humans for food so they're going to be having a bit of a famine sortage in addition to their war. If they can keep ahead of all the raiders they should be fine as they have some food production. Whether this is above or below ground is something to consider.

Then you have the fact that all the nearby lakes and rivers, because this drained lake is the lowest one from a geological standpoint, are going to be slowly drained of all their water they attempt to fill up the lake so any creatures that are dependent upon water or their food is going to start heading downstream trying to find more water and follow food.

then you have the drow which are going to find a way up to the surface with or without going through the dwarfs and are going to be roaming the countryside trying to figure out what's going on.


one month after
Restov - rest of in most of the land south of the valley of fire want to be their own kingdom again they're probably going to declare independence if things are going very very poorly for everyone else. They're not reliant upon the lake in any way for water so they are fine. in fact they're probably the most stable kingdom that's going to be around after the end of it. If the AP I mentioned previously has not started it likely won't.

Numeria - the slaver nation is going to hit the southern lands hard. The barbarian tribes might move in for more ideal land. Machine constructs might wander in with the confusion. Numeria does have not so subtle sci fi elements.

Iobaria - a realm with little in the way of resources and once a place of great Cyclopian empires long before any kingdom here. Defences would of been built and those might be failing. Whether from food or men diverted to more important places. The one eyes are by no means unified but raiders might become more organized as they try and get more fertile land. Especially to the south.



.......

So most thorps and hamlets along the rivers and lakes will be quickly whiped off the map in a matter of days or weeks. Most cities in the area might crumble. Towns and villages should be alright; they have the size to resist invaders and produce enough food for everyone.


By a year the map might need to be redrawn.

LordCdrMilitant
2020-11-30, 07:47 PM
Hello everybody!

In my Pathfinder campaign beneath Lake Reykal there was an enormous system of tunnels and caves which completely collapsed after my players fought some Neothelids there and this caused the lake to get drained completely.

What are the consequences for the nation of Brevoy? Im interessted in the obvious ones as well as in some minor consequences causing interesting alterations to the surrounding area. And it doesnt have to be setting specific of course - think of the biggest lake within a country that hosts some of the biggest cities as well as the capital gets drained.

https://static.wikia.nocookie.net/pathfinderkingmaker/images/8/8a/Brevoy3-0-0.jpg/revision/latest?cb=20180917153324

I really appreciate your ideas, thanks in advance!

This is an interesting question.

So there are several rivers flowing in and one flowing out. The rivers flow in at a relatively constant rate .

Lake Reykal is pretty bigapproximately 5.3e9 square meters, 2000 square miles, in surface area. It's basically not going to drain very fast, so it's not going to be an apocalypse. Specifically, the rate at which it drains is the rate at which water flows into the tunnels [volume/time] minus the rate at which water flows into the lake from the rivers [volume/time], divided by the surface area of the lake [area]. There's a fixed maximum flow rate for water through a hole, and while the hole will be naturally expanded by erosion over time, it doesn't really matter how big the caverns are in total, it matters how big the hole is. It's possible that the lake won't even notice. It's not like flushing a toilet.

Also, unless the tunnels are connected to the ocean, then the lake will fill back up to it's former level in time once the tunnels fill, and this won't take too long, at most a few years. Navigable rivers move a lot of water.


For the duration of the draining period, there will be some reduction in flow down the east sellen river. At some point, the lake may drop low enough to completely cut off that river. This would be very bad for the downriver communities, since it's a minimum of 1 year a maximum of several of famine as they can't water their crops. For the people on the lake itself, things won't be as bad, since the water level won't fall that quickly, and will eventually recover. There might be some panic over the receding shoreline, and also the docks would need moving. The drying up of the east sellen would negatively affect trade with the stolen lands, but given that the rest of the kingdom is upriver, it won't really affect internal trade.


If the caverns are attached to the ocean, [i]and they have the capacity to take the entirety of the east sellen river, then the consequences would be more drastic. The stolen lands would become much less fertile, permanently. The lake would become a river valley where the Awzera and East Sellen meet and then run underground, and the lakeside communities would have to move towards the river path down to the bottom. River trade would come to a halt, but the communities would survive after a bit of relocation to follow the water.

RifleAvenger
2020-11-30, 08:02 PM
This is an interesting question.

So there are several rivers flowing in and one flowing out. The rivers flow in at a relatively constant rate [it varies by season, but like it doesn't care that there's a hole in the bottom of the lake].

Lake Reykal is pretty bigapproximately 5.3e9 square meters, 2000 square miles, in surface area. It's basically not going to drain very fast, so it's not going to be an apocalypse. Specifically, the rate at which it drains is the rate at which water flows into the tunnels [volume/time] minus the rate at which water flows into the lake from the rivers [volume/time], divided by the surface area of the lake [area]. There's a fixed maximum flow rate for water through a hole, and while the hole will be naturally expanded by erosion over time, it doesn't really matter how big the caverns are in total, it matters how big the hole is. It's possible that the lake won't even notice. It's not like flushing a toilet.

Also, unless the tunnels are connected to the ocean, then the lake will fill back up to it's former level in time once the tunnels fill, and this won't take too long, at most a few years. Navigable rivers move a lot of water.

If we're to take the OP's account at face value, then the entire lake must have drained. Which means this was already a losing stream type environment where the water table is significantly below the surface, somehow mitigated by an expansive low permeability unit as suggested by Friv.

Now that there's a direct line to less impermeable units, I'm not sure the lake would return to its prior depth particularly soon. Though it certainly should eventually unless the subsurface geology is incredibly strange (like caverns all the way to the ocean, as you suggested).

That said, the lake draining like a bathtub suggests the GM didn't take hydrology into account much to begin with. As does the use of the Darklands/Underdark. There are certainly expansive dry cave systems in the world, I've been in a few of them, but no continent to world spanning ones. If there were, a substantial amount of them would be flooded, which doesn't tend to fit the usual depiction of the underworlds of D&D and its successors.

LordCdrMilitant
2020-11-30, 08:26 PM
If we're to take the OP's account at face value, then the entire lake must have drained. Which means this was already a losing stream type environment where the water table is significantly below the surface, somehow mitigated by an expansive low permeability unit as suggested by Friv.

Now that there's a direct line to less impermeable units, I'm not sure the lake would return to its prior depth particularly soon. Though it certainly should eventually unless the subsurface geology is incredibly strange (like caverns all the way to the ocean, as you suggested).

That said, the lake draining like a bathtub suggests the GM didn't take hydrology into account much to begin with. As does the use of the Darklands/Underdark. There are certainly expansive dry cave systems in the world, I've been in a few of them, but no continent to world spanning ones. If there were, a substantial amount of them would be flooded, which doesn't tend to fit the usual depiction of the underworlds of D&D and its successors.

Even if the under layer is substantially more permeable, If the lake can drain to a significant degree at all, I would expect it to be no more than a few years for the lake to return to its previous levels. More relevantly, the lake draining at all is unreasonable. There's a drastic difference in scale between a lake and a bathtub.

In either case, the worst case scenario is the lake turns into a river valley that then flows underground. This is not catastrophic for either New Stetven or Silverhall. Silverhall is on a lake entrance, so it's basically unaffected access to water wise. Lake Reykal is 45mi tall at it's tallest point, which is over by Silverhall. The lake is like 20 miles wide, if even, by New Stetven, so at most they're going to be like 10 miles from the river after the draining. All things considered, an engineering project could probably preserve the river's flow right to them, or the farms would just move closer to the river.

The uncovered land is likely to be silt or rocks, as A: the lake is freshwater, B: has natural outflows, and C: is pre-industrial, so it's not at all like the Aral Sea or Owen's Lake or anything like that. It's not going to leave salt flats and toxic fields behind.


Downriver, in the stolen lands, that's going to be another story. But apart from temporary trade disruptions between Stetven and Silverhall and possibly some people losing money, I can't see much happening for the kingdom of Brevoy

RifleAvenger
2020-11-30, 08:41 PM
Reasonable Things

Ultimately, I think, the issue is that the OP, as GM, seems to have already decided that the lake did drain like a bathtub. Which either will involve a lot of work determining the subsurface geology and local hydrology to figure out how that could have even happened...

..., retconning so it didn't actually drain down to nothing...

..., or handwaving the issue and focusing on the immediate aftermath.

I'll admit that I confused the latest response from Alcore with a reply from the OP (Wasum), which is why I mentioned the Underdark at all. I would presume that Alcore's response is true to the published setting lore, but trying to figure out how the water table works with a whole damn underworld involved basically forces the third option above, in my opinion. Probably in tandem with the "lake becomes a river valley" outcome, since the Underdark could well reach to the ocean.

Alcore
2020-11-30, 09:02 PM
I'll admit that I confused the latest response from Alcore with a reply from the OP (Wasum), which is why I mentioned the Underdark at all. I would presume that Alcore's response is true to the published setting lore, but trying to figure out how the water table works with a whole damn underworld involved basically forces the third option above, in my opinion. Probably in tandem with the "lake becomes a river valley" outcome, since the Underdark could well reach to the ocean.
It is partially published setting with some educated guesswork thrown in for the dwarves (been so long i might have the wrong mountain but dwarves are nearby in plentatude). Dwarves were once an Underdark race and they tunnel up to the surface. In their golden age they held nearly all entrances. I am happy to try and answer any question you have. Underdark is not my prefered place though.


Most of my words stem from long use of Kingmaker and extra research surrounding it. I know the general area here better than any other area i have not written myself.

Duff
2020-11-30, 09:05 PM
Some really rough maths. This ignore any change to inflow and outflow speeds. Inflow speed will increase and river outflow will decrease.
Feel free to add assumptions about river flow if you want.

The lake looks like its about 2Km north/south and 4 Km east/west and is more or less a right angle triangle.
So it's surface area is about 2Km2. That's 2,000,000 m2
Water goes through a pipe at about 3m/s. That's a plumber's estimate, but it's good enough for "There's a hole in the bottom of the lake, and the water is somewhere between flowing and falling, but there's all sorts of debris and silt and rough cavern walls involved as well"

So, a hole 1m2 would take 2mil/3 seconds (185 hours) to lower the water by 1 meter.
a hole of 185m2 will drop it by a meter per hour. 185/3.14 (close enough to pi) =59 square root 59=7.5

So that's a hole with a radius of about 7.5 meters. Not a small hole, but not really huger either.


All this assumes geology to have rivers on the surface (so high water table or river beds which are impermeable) and a huge cave system which isn't flooded.

RifleAvenger
2020-11-30, 09:45 PM
I find it dubious there would be such a clean hole pierced into the lake bottom of that size. More likely a segment of the cavern collapsed, resulting in far more numerous, but much smaller, fractures. Settling of debris and sediment within the fractures would also restrict flow.


All this assumes geology to have rivers on the surface (so high water table or river beds which are impermeable) and a huge cave system which isn't flooded.

The water table can't be high, or else the cave systems would already be flooded and the lake would never have drained. Very few types of rock are so impermeable that they can completely stop the infiltration of water over geologic time, and those rock types don't form caves (except maybe lava tubes).

So, essentially, we're looking at a massive perched aquifer that has an expansive cave system below the impermeable unit and above the water table. Knocking a hole in the impermeable layer essentially creates a "shortcut" for the water. Following this preferential pathway, the water will flow through the cavern system until it hits the water table (or becomes perched again by another impermeable unit). If the caverns don't reach the ocean, the water will either be discharged as a spring (if still perched), be released into a surface water system that intersects the water table, be stored in an aquifer, or slowly make its way to the ocean as groundwater flow.

The more I think about it, the more I think LordCdrMilitant's "becomes a river valley and sinks underground" is the immediate outcome given the assumptions we need to make for the scenario to work as described. Whether the lake comes back at all depends on the size and shape of the cavern system, the permeability of the rock, etc. Even if the cave system doesn't reach the ocean, the breaching of the perched aquifer releases the water to infiltrate through the expansive vadose zone below (we know its expansive because it has a deep and extensive dry cavern system) and it could discharge to the surface somewhere to the south.

The only way the lake will return to being a lake is if the flow belowground is sufficiently slow that the water is bottlenecked and backs up as though it were dammed. Even so, assuming equal intake to pre-breach, the lake won't return to its original depth, since a significant amount of water is now flowing through or filling the caverns and vadose zone below the breach.
----------------
Another seeming consequence of this setup is that drilling wells to relieve the water crisis to the south may be difficult to infeasible if the water table is hundreds to thousands of feet underground. Especially in a pre-industrial society (magic though?).

Duff
2020-11-30, 10:43 PM
I find it dubious there would be such a clean hole pierced into the lake bottom of that size. More likely a segment of the cavern collapsed, resulting in far more numerous, but much smaller, fractures. Settling of debris and sediment within the fractures would also restrict flow.



The water table can't be high, or else the cave systems would already be flooded and the lake would never have drained. Very few types of rock are so impermeable that they can completely stop the infiltration of water over geologic time, and those rock types don't form caves (except maybe lava tubes).



I agree - neat holes are pretty unlikely. But a round hole is easy to visualise, so our OP can more easily make decisions about how quickly the water level might be dropping. 1 meter per hour? 10? Only a meter a day? Makes a big difference to how people can respond

A high water table and dry caves is pretty unlikely I agree. It would need the caves to be sealed away from the water somehow - whatever combination of geology and magic you care for.

LordCdrMilitant
2020-12-01, 12:52 AM
Some really rough maths. This ignore any change to inflow and outflow speeds. Inflow speed will increase and river outflow will decrease.
Feel free to add assumptions about river flow if you want.

The lake looks like its about 2Km north/south and 4 Km east/west and is more or less a right angle triangle.
So it's surface area is about 2Km2. That's 2,000,000 m2
Water goes through a pipe at about 3m/s. That's a plumber's estimate, but it's good enough for "There's a hole in the bottom of the lake, and the water is somewhere between flowing and falling, but there's all sorts of debris and silt and rough cavern walls involved as well"

So, a hole 1m2 would take 2mil/3 seconds (185 hours) to lower the water by 1 meter.
a hole of 185m2 will drop it by a meter per hour. 185/3.14 (close enough to pi) =59 square root 59=7.5

So that's a hole with a radius of about 7.5 meters. Not a small hole, but not really huger either.


All this assumes geology to have rivers on the surface (so high water table or river beds which are impermeable) and a huge cave system which isn't flooded.

The lake is 90 miles by 45 miles according to the Pathfinder wiki https://pathfinderwiki.com/wiki/Lake_Reykal




I find it dubious there would be such a clean hole pierced into the lake bottom of that size. More likely a segment of the cavern collapsed, resulting in far more numerous, but much smaller, fractures. Settling of debris and sediment within the fractures would also restrict flow.

The water table can't be high, or else the cave systems would already be flooded and the lake would never have drained. Very few types of rock are so impermeable that they can completely stop the infiltration of water over geologic time, and those rock types don't form caves (except maybe lava tubes).

So, essentially, we're looking at a massive perched aquifer that has an expansive cave system below the impermeable unit and above the water table. Knocking a hole in the impermeable layer essentially creates a "shortcut" for the water. Following this preferential pathway, the water will flow through the cavern system until it hits the water table (or becomes perched again by another impermeable unit). If the caverns don't reach the ocean, the water will either be discharged as a spring (if still perched), be released into a surface water system that intersects the water table, be stored in an aquifer, or slowly make its way to the ocean as groundwater flow.

The more I think about it, the more I think LordCdrMilitant's "becomes a river valley and sinks underground" is the immediate outcome given the assumptions we need to make for the scenario to work as described. Whether the lake comes back at all depends on the size and shape of the cavern system, the permeability of the rock, etc. Even if the cave system doesn't reach the ocean, the breaching of the perched aquifer releases the water to infiltrate through the expansive vadose zone below (we know its expansive because it has a deep and extensive dry cavern system) and it could discharge to the surface somewhere to the south.

The only way the lake will return to being a lake is if the flow belowground is sufficiently slow that the water is bottlenecked and backs up as though it were dammed. Even so, assuming equal intake to pre-breach, the lake won't return to its original depth, since a significant amount of water is now flowing through or filling the caverns and vadose zone below the breach.
----------------
Another seeming consequence of this setup is that drilling wells to relieve the water crisis to the south may be difficult to infeasible if the water table is hundreds to thousands of feet underground. Especially in a pre-industrial society (magic though?).


Ultimately, I think, the issue is that the OP, as GM, seems to have already decided that the lake did drain like a bathtub. Which either will involve a lot of work determining the subsurface geology and local hydrology to figure out how that could have even happened...

..., retconning so it didn't actually drain down to nothing...

..., or handwaving the issue and focusing on the immediate aftermath.

I'll admit that I confused the latest response from Alcore with a reply from the OP (Wasum), which is why I mentioned the Underdark at all. I would presume that Alcore's response is true to the published setting lore, but trying to figure out how the water table works with a whole damn underworld involved basically forces the third option above, in my opinion. Probably in tandem with the "lake becomes a river valley" outcome, since the Underdark could well reach to the ocean.


I think we're largely in agreement.


There's all sorts of messed up with the region's water flow:
https://pathfinderwiki.com/mediawiki/images/2/22/Map_of_Brevoy_and_its_neighbors.jpg

I'm not actually certain it would be drastically catastrophic downriver on the east sellen anymore based on this map I found. It's not actually that far until there's a more-east sellen that feeds in south of that swamp. That swamp also happens to have 4 more small rivers feeding it, so while the stretch of the East Sellen between New Stetven and Lake Hooktongue would disappear, and Lake Hooktounge would shrink drastically, downstream of that it would probably only go noticed as a slightly decreased water level.

Also, the swamp's existence seems to imply that the water table comes up to the surface there, which makes whatever's going on super weird. I'm not a geologist though, so maybe some big slab of rock can explain it.

Roger_Druid
2020-12-01, 01:09 AM
Hi all!

You might want to read "Star of Cursrah", 21322, a WoC novel by Clayton Emery, that deals with a river changing bed and a whole city-state being wiped out...

Roger Druid

LordCdrMilitant
2020-12-01, 01:13 AM
Hi all!

You might want to read "Star of Cursrah", 21322, a WoC novel by Clayton Emery, that deals with a river changing bed and a whole city-state being wiped out...

Roger Druid

I wouldn't ordinarily place stock in fiction writers to guesstimate what would happen, but in this case, there are also actual historical examples of a river moving and a community disappearing.


That said, in this case, the river isn't moving that far. It's not moving at all for Silverhall, since Silverhall is upstream the disruption, and the lake is 45 miles wide at it's tallest point, and it looks about half that wide around New Stetven, so they're only going to be like 10 miles from the new riverline.

And then there's nothing between the point where the river no longer continues and where the next river bunch joins in. Mivon is the next downriver city, and it's at the convergence of the East Sellen and the Shrike.

Incorrect
2020-12-01, 02:42 AM
The Stolen Lands to the south will be hit very hard. It might depend on when in the Kingmaker campaign path this happens. If its a small barony it just dies from failing crops and lack of transportation. If the campaign is complete, The Stolen Lands is ruled by several level 20 characters, and they will probably spend about 1 hour fixing the problem.

Other things that might happen.

The lake transforms into a swamp of dead and decomposing fish, animals and plants. It will be known as the Age of Stench.

Engineering and mages guilds, work together to seal the gaps. It is a costly project. In the end, the seals form artificial islands in the lake as it fills up again.
Mages and engineers start inhabiting these islands, creating their own society.

An old man called Chresten loses his favorite fishing spot. This seems like a minute detail, but he saw who is responsible for the disaster, and he is bitter. So bitter in fact that he starts a campaign to punish them. It gains a lot of traction, and Chresten finds himself leading hundreds of starving villagers in a hunt to catch and punish those responsible. He is generally a Good guy, but he feels strongly that anyone causing children to starve should be brought to justice.

LibraryOgre
2020-12-01, 08:52 AM
The dried out lake bed will make for some amazing dust storms. If it goes like the Aral sea in Kazakhstan, the lakebed and dust will be toxic. So blowing dust could make the surrounding area a bit nightmarish. Cities where everyone wants to go, all the wealth is gone, everyone who's able to travel reasonably easily is gone and desperate people sell whatever they can to buy the food that people are willing to bring.
It could get a bit apocalyptic

This would be my inspiration, TBH. The draining of the Aral Sea has had some well-established real-world consequences, and so you should look there for a good example of the mundane impact. If you've got some Dragonlance stuff, you might also look at the effects on Tarsis, which wound up land-locked after the Cataclysm.

As someone said upthread, there may be fantasy consequences... what's going to come in to the place that once was an inland sea? Will it be water-loving humanoids from the deep? Will it be para-elementals attracted by the ooze or salt? Will you have a necromantic event? Was something being contained by the water of the lake (simple answer: Ancient Vampire, buried in a coffin under the water, unable to leave because running water would destroy them)?

LordCdrMilitant
2020-12-01, 05:56 PM
This would be my inspiration, TBH. The draining of the Aral Sea has had some well-established real-world consequences, and so you should look there for a good example of the mundane impact. If you've got some Dragonlance stuff, you might also look at the effects on Tarsis, which wound up land-locked after the Cataclysm.

The Aral Sea and Owens Lake are both dangerous because they are endoheric basins. Lakes with no water outflow, and are thus salt lakes. When they dry up, they leave salt flats behind.

Lake Reykal is not that. It's a large freshwater lake with significant natural outflow. So it won't leave a toxic salt flat behind when it dries up. In addition, draining and drying up are different, since the salt falls out of suspension when water evaporates, but it would mostly drain deeper into the ground if the water ran out through a tunnel.

Duff
2020-12-01, 07:00 PM
The Aral Sea and Owens Lake are both dangerous because they are endoheric basins. Lakes with no water outflow, and are thus salt lakes. When they dry up, they leave salt flats behind.

Lake Reykal is not that. It's a large freshwater lake with significant natural outflow. So it won't leave a toxic salt flat behind when it dries up. In addition, draining and drying up are different, since the salt falls out of suspension when water evaporates, but it would mostly drain deeper into the ground if the water ran out through a tunnel.

Good points, both. The Aral wasn't very salty, but on further investigation, it looks like the reason the dust is toxic is a combination of salt and chemicals (mostly pesticides). Still, dried out lakebed will make for epic dust storms and the chemistry or the dust will be affected by having been being wet and anaerobic.

Also, I misread the scale. I think the "hole" needs an extra 0. That would mean a radius of 75 meters to drop it by a meter/hr.

That's a lot of hole and a huge empty space underground to fill.

LordCdrMilitant
2020-12-01, 07:35 PM
Good points, both. The Aral wasn't very salty, but on further investigation, it looks like the reason the dust is toxic is a combination of salt and chemicals (mostly pesticides). Still, dried out lakebed will make for epic dust storms and the chemistry or the dust will be affected by having been being wet and anaerobic.

Also, I misread the scale. I think the "hole" needs an extra 0. That would mean a radius of 75 meters to drop it by a meter/hr.

That's a lot of hole and a huge empty space underground to fill.

Poyang Lake turned into a huge grassland when it dried up, so it could go that way too.

If the environment is natively dry, then it might turn into a dustbowl. But the area around New Stetven at least is pretty cold and damp, and has snow on the ground for most of the year making everything perpetually muddy.

The lake also isn't drying out, there's still 3 rivers there flowing through the area, they're just flowing underground into a tunnel now instead of out through the East Sellen.

The reclaimed ground might actually be pretty fertile, since it would be easy to irrigate from the rivers.


As someone said upthread, there may be fantasy consequences... what's going to come in to the place that once was an inland sea? Will it be water-loving humanoids from the deep? Will it be para-elementals attracted by the ooze or salt? Will you have a necromantic event? Was something being contained by the water of the lake (simple answer: Ancient Vampire, buried in a coffin under the water, unable to leave because running water would destroy them)?

This may just be Katherine lacking in imagination, but I think the realistic and logically following human consequences are potentially far more interesting than fantastical or contrived problems of the usual fantasy sort. Oh no! The sea monster is angry, better stick it with a sword... but real consequences like humanitarian crises and politics don't go away because you spent 8 6-second rounds sticking it with a pointy.

I've seen far too many stories and games where the heroes kill Baddy MacBad and foil his nefarious schemes and everything then just suddenly goes back to normal and everything is fine with no attention paid to the lasting effects of conflict and disasters.



There's already a civil war brewing in Brevoy as a consequence of a succession crisis, as the reigning family vanished without a trace and the lord of Issia, the northern half of the kingdom, declared himself the new king, but the people of Rostland, the southern half, oppose this ascension. There will certainly be plays for power by noble households, given that a significant part of the wealth of New Stetven comes from controlling the trade along the East Sellen, and sitting right atop the trade line between Rostland and Issia. The king's throne itself may be in jeopardy from both a secession crisis, nobles playing to usurp each other, and power plays from perceived weakness in a time a relative crisis.

Rostland is the breadbasket of Brevoy. While the parts near the Shrike river by Retov won't be affected directly by water problems, parts in the west near the East Sellen and Hooktounge Slough may find themselves unable to continue farming their land without water. Trade will be disrupted and there may be food shortages in Issia as a consequence of supply line disruption. Refugees will flood into Restov, New Stetven, and Silverhall from both Rostland and from the Stolen Lands, taxing their infrastructure that's already over burdened by the disaster.

Fishermen will be instantaneously deprived of their livelihoods. Sudden and high unemployment + a refugee crisis is a recipe for serious unrest amidst the masses.

Wasum
2020-12-01, 09:29 PM
Wow, thanks to you all for these great ideas and information on handling the simulation of such an event!

I guess I owe you at least some context to embed this situation of my campaign - I'll summarize the chronology:

The story takes place in the setting of the Kingmaker AP with some alterations, especially towards the different factions (including the houses) but its roughly close to the beginning of the AP. Brevoy was conquered by Choral two hundred years earlier who then disappeared, leaving behind the noble house of rogarvia - his people - established as rouling house in Brevoy for years to come. About ten years before the begin of the campaign all Rogarvias disappeared, leaving behind no traces and the house of Surtowa, ruled by the ever absent king Noleski Surtowa fills up the power vacuum.

Also, there is one powerful wizard in Magnimar, a necromancer, led by the forces of Abaddon who is interested to revive the lich resting somewhere in far north east of the continent. He establishes a network in the region to get adventurers to find hidden cyclops sites hoping to get information about their whereabouts or - even better - have them unseal the tomb of said cyclops lich. The party had just established a settlement in the so called Greenbelt south of Brevoy when the inevitable event occurred and they first found, later opened an old tomb of a graveknight cyclops, a fellow of the lich Vordakai, who then after thousand years of sleep fled to free his master.

In the meantime a new player entered the game as a noble appearing adventuress suffering from memory loss - only some flashes of images is left for her to remember. But these vague images lead the players to an old tome which then is way to powerful for them to even touch and therefore is sealed by the group until they have the right tools to deal with the artifact. Over the course of several other story arcs there develops a small subplot for the aforementioned player that informs her that her character has died once before and is somehow connected to the House of Rogarvia. Investigating an old, abandoned estate they find out that said character indeed once was part of the royal house - even though in a minor path of the family and was even buried close to the property - but the coffin is found empty with just a little note - an apology from her brother who happened to be an old friend of Noleski. Her death was dated back close to the time before the Rogarvias disappeared and over the course of a large scale trip to literal hell they find out that her origin is that of the first humans on Golarion. Some elder being sent the first humans to Golarion in order to open a gate there for the deity to traspass. But when those first humans came to earth they faced a prospering nation of cyclops, followers of the four horsemen and led by the lich Vordakai and his deacons. There's war for decades and with the help of an abyssal artifact and old elven technology they manage to banish all humans to a prison plane, resulting in a defeat of human life on Golarion. At least if it wasn't for aboleths. Those creatures (and to keep as close to Golarion lore as possible) resurrected some of the fallen human whose corpses where left behind by the cyclops because they were fascinated by those adaptive creatures. This event is recorded as the dawn of men, the resurrected humans from outer space were the ancestors for all living and extinct human zivilisations on the planet.

In the meantime the lich plans his comeback, farming ressources, buying weapons, recruiting armys and interfering with politics and even starting a war between two houses while preparing his attack on Brevoy. For a long time he tries not to appear as the madlich he is until he manages to absorb the first city of Brevoy - Restov (which had just found peace months before) - to his new realms, transfering the willing to his new city and the unwilling to undeath. Soon his army starts marching to the north, interessted in reclaiming one of the most important sites of his former kingdom - the so called skywatch which hosts the very elven technology that dealt with those humans thousands of years ago. The building is under intense protection from Noleski who is actually an immortal novelist seeking for a timeless place to eternaly rest with his love, afraid of - again - outliving her. He's a wicked romantic in my campaign. He secretly made the skywatch his residence as he used the wealth of the Brevian throne and the ancient power of the ancient site - still based on elven technology - to create his demiplane of desire.

The lich's kingdom eventually becomes strong enough to annex the players realm, by now evolved to a respected and fast growing extension of northern Civilisations with increasing influence on Brevian politics. Its about then when the players restore the memories of the Rogarvian character and get to know that Choral the conquerer and his followers, the noble house of Rogarvia, where some kind of cultists who plan to call an older deity to the planet. She lost her memories because she violated a vow to keep their plans secret as she tells her brother and Noleski about whats going on. Those two friends decide to get rid of the Rogarvias using the skywatch which they had plausible reasons to know about but both didnt want to kill the players character. So they kill her right before banishing all Rogarvias just to revive her afterwards. The brother leaves to seek for redemption, Noleski becomes king as he fulfilled a deal he made with the house of Surtowa. And of course the respective character also remembers where the ritual to call the elder being takes place - the enormous caves beneath the reykal lake. Wow, now that you read all that - here's finally the relevant part concerning my question! They decide to visit said place but the project accompanied by unfortunate circumstances. The wish spell who granted back the memories was cast by a glabrezu they encountered in the skywatch - kind of an unintended security mechanism of the site and Noleski. The wishs other side of the coin is the tradegy which follows the memory restauration - in a succession of unfavorable events containing troglodyte civilizations, their mad priests and neothelids the whole cave system (where talking underdark) collapses in an earthquake which causes the sea to flood the place and powering the elder being presence just by the appearance of the one character I always talk about - missing the opportunity to name her for all sakes. Thats for the context so far, I left out a bunch of links between different story arcs but just please just go along so far, in my head everything has elaborated reasons.




What happened in the next session is that slowly the water in the lake became rougher as a spiral stream made it difficult for ships to navigate and the water level slowly fell (but in reasonable measures - no toilet flush!). The turbulences in the lake caused damage to the poor districts of New Stetven (which in my campaign are built as wooden docks) as well as to Silverhall where the respective river became a current. Now I need to flesh out the consequences more thoroughly and find a lot of great advice from you on here. I will adept the advice towards food shortages - those seem really plausible as well as those towards the trade routes collapsing. I didnt have close as many economical and ecological consequences on mind as you mentioned here. I also like the idea that in the end there will be a new sight in the region - a huge delta of waterfalls plunging into the depts.

Also the influence of the elder being now strengthened will result in some weird phenomenons in the area - weird glows in the draining lake and maybe even a cult of fishermen, controlled by that very being, establishing in Neu Stetven helping feed the masses and pushing for the influence of the elder deity. Further - just in a few days the first battle between Brevoy and the lich's armies will occur north of the Gronzi Forest so for now ressources of the nation will be distributed accordingly.

Also I think it would be very plausible for Silverhall to build a dam to ensure the port will remain functional, at least in one direction. On the long run reestablishing a connection to the east sellen river should be inevitable.

I still have to sift through all your comments so there's still more to flesh out and of course I still appreciate all your further ideas on this matter.


tl/dr: its fine :)



Thanks,
Wasum

LordCdrMilitant
2020-12-01, 10:57 PM
What happened in the next session is that slowly the water in the lake became rougher as a spiral stream made it difficult for ships to navigate and the water level slowly fell (but in reasonable measures - no toilet flush!). The turbulences in the lake caused damage to the poor districts of New Stetven (which in my campaign are built as wooden docks) as well as to Silverhall where the respective river became a current. Now I need to flesh out the consequences more thoroughly and find a lot of great advice from you on here. I will adept the advice towards food shortages - those seem really plausible as well as those towards the trade routes collapsing. I didnt have close as many economical and ecological consequences on mind as you mentioned here. I also like the idea that in the end there will be a new sight in the region - a huge delta of waterfalls plunging into the depts.

Also the influence of the elder being now strengthened will result in some weird phenomenons in the area - weird glows in the draining lake and maybe even a cult of fishermen, controlled by that very being, establishing in Neu Stetven helping feed the masses and pushing for the influence of the elder deity. Further - just in a few days the first battle between Brevoy and the lich's armies will occur north of the Gronzi Forest so for now ressources of the nation will be distributed accordingly.

Also I think it would be very plausible for Silverhall to build a dam to ensure the port will remain functional, at least in one direction. On the long run reestablishing a connection to the east sellen river should be inevitable.

Wasum

Silverhall wouldn't need a dam to navigate upriver. The lake draining almost won't affect them at all since their river runs into the lake so they're upstream of the disturbance.

Also, unless the lake is like monster deep like lake baikal, which it almost certainly isn't if it has caves underneath it, or in a dammed valley [which is also isn't] it will have a relatively flat and silty bottom which will create a sort of bowl-shaped u-valley that the rivers flow through to the hole that they meet and go underground at.

There might be a waterfall or two of the tumbly downslope-over-rocks kind as it transitions from shallows to deeper areas, but it's also worth mention that the new course off the rivers through the valley will pass through more easily eroded silt sediment from the lake bed rather than going over rocks.