Just want to make sure I'm not overlooking anything obvious here.
The annis hags get to use control weather daily to create heavy rains for days on end, threatening the dam. The spell only affects a two-mile radius, and given the apparent size of the Storval Deep it seems like it would take torrential rain over a much larger area to raise the level of the reservoir at all. Heavy rains south of the dam could certainly cause the river to overflow its banks and flood Turtleback Ferry. I don't want to skip the encounters at Skull's Crossing, I'm just not sure how to make sense of this.
My general impression (perhaps a false impression) is that the unnatural weather manifests heavy rain at Turtleback, at Fort Rannick and at Skull Crossing. But that's roughly 25 miles of river and again, the spell only covers a two-mile radius. For that matter it only has a two-mile range, and the covey is quartered at Hook Mountain, something like 20 miles away from the river. Maybe it only rains heavily on the mountain, and is carried down to the river by streams. Again, doesn't fit the impression I had of widespread extreme weather. Or the hags can hike down the mountain, cast their spell and either hike back or set up a temporary camp someplace. No such temporary camp is hinted at. I'm also not clear when the heavy rains start and over how many days they continue until the ogres break the dam.
If all goes as described in the module it appears that Turtleback Ferry will flood twice: abruptly the first time and gradually after the floodgates are opened. I've seen a couple of player created maps of the flooded town. Should these represent both flood periods (that is, should both flood periods reach the same level) and will the town remain partially flooded until the dam is eventually repaired, or are the waters supposed to recede after a few days even with the dam in its damaged state?
I regard the rains more as flavor, and a way to make sure that the water level is sufficiently high. The real flood is caused by the ogres busting the dam (which, by the way, makes me regret not having a sound system in play). The worse second flood would come if the dam can't regulate the water flow, thus bursting totally.
The torrential rain above the mountain makes it harder for travelers, thus making sure that no pesky hunters (or black arrow rangers) notice what's going on. That the mountain range is perpetually shrouded in storms will be visible from Turtleback Ferry, and it will definitely make the weather and the water level worse, even at that range.
Considering that the players will have to decrease the pressure by opening the flood gates, the water level of the immediate area will remain like that for a while. And then the frost will come. It won't be an easy winter for the people of Turtleback Ferry, so I hope that the new management of Fort Rannick knows what they're doing…
(Ceterum censeo: The distances in HMM seem a bit off anyway. Magnimar has a minor fort as a dependent 450 miles away? Definitely written by a male American…)
The worse second flood would come if the dam can't regulate the water flow, thus bursting totally.
The second flood I mentioned was a consequence of opening the floodgates; the AP text notes the waters rise again but more slowly. I'm confident the group can avoid the dam bursting, which would destroy the town completely.
The torrential rain above the mountain makes it harder for travelers, and it will definitely make the weather and the water level worse, even at that range.
I hadn't considered that storms above Hook Mountain would be visible from the Fort or the Ferry, but that's a good point -- the weather doesn't have to be on top of you to be noticeable and a cause of concern, and it will affect the water level downslope. It doesn't seem like it would affect overland travel at a distance, though.
I still want to pull together some kind of rough timetable for when the rains start -- days before the ogres break the dam, or weeks before?
I hope that the new management of Fort Rannick knows what they're doing…
Magnimar has a minor fort as a dependent 450 miles away?
The distance from Magnimar to Ft. Rannick didn't trouble me, as it's not really intended to be of any benefit to Magnimar other than a way to keep the strategically located Turtleback Ferry out of Korvosan hands. New management for the fort could be a problem, though. I really can't see my group [of players] being interested in the job. There is one character in the group who might jump at the opportunity, but that would mean his player would have to change characters mid-stream again and I don't know how well that would go over.
(I should mention at this point that our group is strongly in favor of continuity and really tries to avoid games where TPKs or near TPKs result in a high turnover of PCs. Some of our campaigns have run for years with no need of replacing characters (raising them from the dead, yes, but not switching to another PC mid-adventure if it can be helped.)
I got the feeling that the timeline of the adventure was a bit stretched out, due to the events on the Paradise in Turtleback Ferry being cut. It shouldn't really matter a lot, as the Storval Deep is about 100 miles long. Yes, the adventure says that the covey made sure that the water level "near to the Storval side of the dam are properly swollen". Which looks to me like someone didn't put any points in Knowledge (fluid mechanics)…
Personally, I'd make it perpetually rain for the whole time, i.e. since before the ogres attacked the fort (Actually, shortly after Paradise was burnt down). This already creates a pretty high water level in the rivers, kinda preparing the waterways for the real flood that will follow. Also, rain helps the ogres attack the fort. They're more the melee guys, so decreased accuracy of the ranger's bows (-4 in rain, IIRC) really helps. Wet eagles don't fly that well, too.
It's also somewhat foreboding. The people in Turtleback Ferry are already worried about floods as it is when the players arrive. It's also a good reason why (almost) every member of the Graul familiy is at home all the time. And when they're riding towards Fort Rannick, they ride to the edge of the worst storm, always a nice picture. It's gonna be a muddy fight…
And yes, I don't think my players will take over Fort Rannick, too. Sandpoint is supposed to be the base for a long time, now there's already the lure of Magnimar, and now lordship? (Right when they reach "name level", by the way. Nice touch, Paizo.) Them being nice guys, I think they will stay for the winter, though. There's gonna be a lot of refugees from Turtleback Ferry and other villages and they need help.
One other thing about 450 miles from Magnimar.
If Magnimar has weather approximately equil to Seattle, then 450 miles inland would have weather approximately equil to ... Missoula, Montana!
In other words, we are not talking rains at that point but Snow!
And, if you look at the geography of Turtleback Ferry, there is quite a bit more water. Which means even deeper snow - like the 3-4 feet that they get near the Great Lakes.
If Magnimar has weather approximately equil to Seattle, then 450 miles inland would have weather approximately equil to Missoula, Montana!
Except that we have a different placement of mountain ranges, so in terms of weather patterns there's no correlation of the land between Magnimar and Ft Rannick with the land between Seattle and Missoula.
Except that we have a different placement of mountain ranges, so in terms of weather patterns there's no correlation of the land between Magnimar and Ft Rannick with the land between Seattle and Missoula.If Magnimar has weather approximately equil to Seattle, then 450 miles inland would have weather approximately equil to Missoula, Montana!
However, we do have 450 miles.
It is true that Conquerer Bay is only 100 miles or so to the south, so would be a bigger influence on Turtleback Ferry's weather. My point is that with the distances involved in the adventure, climates do change - a lot. So while it might be wet and rainy on the coast, it is very likely cold and snowy as you move inland.
Also note: About 200 miles north of Turtleback Ferry, someone is running a huge freezer (Irrisen).
LOL... Ok so, it rains heavy in the fall for some reason, and then BAM it snows the likes of witch nobody has ever seen on earth... ;)
LOL... Ok so, it rains heavy in the fall for some reason, and then BAM it snows the likes of witch nobody has ever seen on earth... ;)
OT, I know... but I fear my group fail Turtleback and the dam will break...
OT, I know... but I fear my group fail Turtleback and the dam will break...
In that case, you can have much of the "percipitation" be in the form of snow - for the reasons I gave above. There would still be enough rain for the first flood since the Ogres will still be damaging the Damn.
(Which you could then use to let your player's "try again" or to have a band of heroes from Korvosa save the day.)
I chose to go the way that the Sisters were using control weather as a lever on the natural weather i.e.:
They were fairykin nobles before, connected to the land, they know how the weather works "naturaly" around there and they have been doing this on a long term.
They were feeding the bad weather in the right place in the montains to afect a wider area.
If a player asked if he could do that with control weather i'd say: "If you take a few non-stop weeks in a land you have known for a good number of years and staying within the normal limits (heavy rain in fall) then O.K."
A kind of "take 20" on a Craft (Weather) skill ;)
For the two phases of flooding, if the water is flow-controled in the "right" channel by the dam's valves (punched fast along a figured line by the skulls rather than spread wide all over the area) most of it could be directed to the lake.
It turns the bomb into a canon I figured.
Thats how I presented it to the group and they found it cool.
Okay, so we've reached the point in the timeline where the dam will crack and the town will be half flooded. When this happens the PCs will be at or above Ft. Rannick. The fort appears to be 5-6 miles from Skull River, so they may be able to see it from the mountainside above the fort.
No way they can stop the water from reaching town, but they may want to make haste back to town to start pitching in on damage control as soon as possible. Once the dam cracks, what's the minimum likely time for the flood wave to hit the town? I don't need to work out details like the slope, infiltration, flow volume, etc. but the water does have to travel 25 miles, and I'd like to have an idea of whether it's more likely to do that in 30 minutes or 3 hours, since there is the possibility that a couple of them could be carried back to town by giant eagles in only a couple of hours.
EDIT: This is the only example I've found online so far; most references just say a flash flood can move "at a high rate of speed" or "with incredible speed" and don't even hint at a range of speeds they think of as "high" or "incredible" --
The Antelope Canyon Flash Flood of August 12, 1997
On the afternoon of August 12, 1997, 12 people were caught in a narrow canyon near Page, Arizona during a flash flood event. Eleven of these people died when a wall of water, estimated to be well over 10 feet in height, swept through the canyon with little notice. The thunderstorm that caused this flash flood occurred miles from the slot canyon, with only a trace of rain reported at the canyon itself. However, about 10 miles upstream from the canyon 1.5 inches of rainfall fell, with 0.75 inches falling in approximately 15 minutes. The water made it into the canyon approximately 30 to 45 minutes later, with sudden and deadly results.
At that rate, 90 minutes to move 25 miles.
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Check this link out for some idea of how fast water can flow in such a catastrophe.
Water surface flow rate (velocity) is determined by the volumetric flow rate (m3/s) and the shape of the land. A narrow channel (like a valley or a slot canyon) will have a much faster surface velocity than a flat flood plain where the surface flow may be difficult to even see but where water levels can be seen to rise slowly over hours/days.
In the upstream part of the Skull River (where I imagine it as an incised river valley), it's not unreasonable to have the water be moving at 20 mi/hr. Downstream, the flooding could be more gradual if you imagine that Turtleback Ferry is built on a fairly flat plain and could be moving more like 5 mi/hr or something for the bottom half or whatever of the river's run.
That said, in my campaign, I would have the river flooding take as long as is dramatic, provided the PCs acted quickly enough. Since it's scientifically reasonable for a group to observe fast rushing waters from the Fort and still be able to hurry on horseback to the town in time to help before the flood peaks, I would have the timeline be as long as it needs to be.
If the PCs sit pat and do nothing, I'd give them an hour or so before the waters start to rise in the town and a few hours past that before the flood peaks.