View Full Version : How does one avoid th River Police?

02-05-2010, 10:39 PM
Short of just posting something with a river in it for review that is. I did some cursory searching but couldn't find a thread on "Real Rivers I Have Known and Policed" or the like.


02-05-2010, 11:15 PM
Here are the basics, there are a whole lot of things to consider but these are the simplest things:

1. Water flows downhill. It will not flow from the plains up and over a mountain chain to some other plains area.
2. Lots of rivers and streams flow into a lake but there is only one that flows out. That one might have some little delta-like thing branching at the start but they will join up to form one river channel and the area with the softest dirt to cut into or the steepest angle to flow down will eventually win out producing one outflowing channel. The known exceptions are: an endorheic basin which forms below sea level so therefore has no outflow; and a crater lake.
3. Rivers wander all over the place and vary in width...flat = fat (generally).
4. Rivers don't split and stay split except in deltas. They may go around a more dense chunk of rock to form and island but they rejoin rather quickly. The reason that they don't rejoin in deltas is that the area is too flat so they wander around like tweens at a sock-hop and they dump into the ocean before they can get a chance to rejoin. This is the biggest thing that people mess up. They usually make these giant deltas and forget about scale. We try to encourage the analogy of a tree - put the branches in the mountains, put the trunk on the plains, and put some tiny tiny roots near the coast.
5. Rivers do not flow so that they connect two oceans or two separate parts of the same ocean. You could have a man-made canal, though.
6. Don't rely on "magic" to explain things away - that's bad physics and would require so much power that only a god could maintain it.

Here is a link to a good discussion:

02-05-2010, 11:15 PM
Try "How to get your rivers in the right place" and "Essential river guidelines"

02-05-2010, 11:58 PM
Awesome! Thanks! I think if I stick to #4, I'll probably be fine. But I'll do my homework.


Mark Oliva
02-06-2010, 01:34 AM
Short of just posting something with a river in it for review that is. I did some cursory searching but couldn't find a thread on "Real Rivers I Have Known and Policed" or the like.


The truth is, you don't always have to avoid the river police. Sometimes you just have to toss them out, saying that they're outside their area of jurisdiction.

Being more serious, the river police are very valuable for people who want rivers in their fantasy RPG setting to flow the way that they do in the real world. But that's also where their jurisdiction ends.

Fantasy and fantasy RPG settings have their roots in mythology, and many mythologies have their own geographical and geological premises that are pretty far removed from those of the real world. So ... if you want to make your setting more or less in the manner that a mythology explained it, you may have to ignore some of the otherwise meritorious rules that the river police want to enforce. On the other hand, once you've mapped in the parts of your mythology-based world that violate the "river rules," you might do well to obey the rules in mapping what's beyond the violated areas. The reason to do that is that your world will have a more natural feel to it and work more down the lines of the logic that players in the setting understand.

My arguments here should lead one to the reasonable conclusion that I - or in my case the entire Vintyri (TM) Project - are among those who intentionally live outside of the jurisdiction of the river police. That's correct. The root of our Jrgar (TM) campaign setting is Eddaic. The Elder and Prosaic Icelandic Eddas are the granddaddy of a large segment of the fantasy RPG and novel markets, including the "Lord of the Rings" trilogy by J.R.R. Tolkien. In fact, Prof. Tolkien offers a prime example of operating outside of police jurisdiction, in his case, the jurisdiction of the mountain police. If they had had their say, the mountains of Mordor would have been banned, and we would have had an entirely different story, if any at all, from Prof. Tolkien.

In the Eddas, the 11 great rivers of the world all flow down from Hvergelmir on Upphafsjall, and from there they flow through great mountain ranges in 11 different directions from due east in a half circle to due west. So, the Jrgar setting does indeed have a single source that feeds 11 rivers, and these 11 rivers forge gorges through great mountains that are without a parallel in the real world. The river police would be out of bounds in that part of the setting. However, once the 11 great rivers have broken through the mountains, they follow the otherwise sensible (in most respects) rules by which the river police work.

However, I think the river police give too little credit to some real world realities that can be very useful in RPG settings:

An old truism (but not one enforced by the river police) tells as that all rivers flow into the sea. The unfortunate thing about truisms is that they're untrue. There are some rivers that never flow into the sea.

We find a prime example in the Bear, Jordan and Weber Rivers, in the state of Utah in the U.S.A. These three rivers flow into the Great Salt Lake on the Bonneville Flats. The Great Salt Lake has no outlet. Its water does not flow into the sea; it evaporates just as sea water does.

This brings us round in something of a circle, where we may be able to find a bit of accuracy in our inaccuracy after all: The Great Salt Lake is what remains of a great inland pluvial sea in prehistoric times.

Another interesting example in the U.S.A. is the link of Lake Tahoe, the Truckee River and Pyramid Lake in the Sierra Nevada Mountains of California and Nevada. Melting snow from the mountains flows down into the Tahoe Basin, which is 1,645 feet/501m deep, forming Lake Tahoe. The great lake has only a single outlet, as the river police demand, the Truckee River.

Nearby Donner Lake also is a part of this system. Its outlet is Donner Creek, a tributary of the Truckee, which flows down Nevada's east face of the Sierra and across the Northern Nevada desert into another basin, Lake Pyramid, which, like the Great Salt Lake, has no outlet.

There also are streams that spring from the ground, forge a course along the surface and then flow into a cave system running underground once more. The Puerto Princessa River in the Philippines is one of the better known examples.

Don't hesitate to break the rules of truisms in the manner Mother Nature does, if it serves your campaign well. But if you do so, follow another of nature's examples: Don't overdo it. Rivers that flow back into the ground or that never reach the sea are exceptions. They should be that in your gaming world too.

02-06-2010, 01:46 AM
Another avoidance is to not "be" the cartographer and actually join the police as a deputy. Agree that the bard that drew this land obviously didn't know the place well, because he put in these implausible rivers. He probably put in other imaginary stuff too - look at that: he put in horses and eagles when anybody knows the dragons and griffins ate the horses and eagles ages ago. That still leaves you "needing" to be realistic in whatever part of the world the mapper honestly knows, but that could be a small subset of the map.

02-06-2010, 01:51 AM
The river policed rules (to coin a phrase) are good ones for making general sense and generally follow a geologically sound pattern based on generalities found in nature, at least on our earth. (and i'll say it again- generally! hah) Regards the river police and inland salt basin seas etc, I've seen those posed as examples many times as exceptions :) If you want to, you can find examples that contradict nearly all of the specific citings that have been handed out (except perhaps water flowing uphill). Of course there are exceptions, but as you point out, that's exactly what they should be - exceptions, not rules.

if your world has it's own rules, i think the call at that point is to ensure that those rules are followed consistently throughout that world. Consistent internal logic is important to the believability, which in my case at least, adds to the enjoyment.

02-06-2010, 02:31 AM
I appreciate all the responses. I was mostly looking for a reference to the articles listed above because I figured they existed but couldn't find them <cough>because I'm too lazy to look real hard</cough>. I'm less worried about "breaking the rules" than I am about making a map that looks good.

Ansel Adams said "The great is the enemy of the good" or some such, but everyone here is so friendly and helpful, that I see a lot of good cartographers becoming great. I just wanna be one of them :D


02-06-2010, 02:37 AM
Excellent plan, it worked for me :)

And sometimes threads take on a life of their own and get away from you. Don't worry too much when it happens :P

02-06-2010, 08:49 AM
There are even some unique cases in which water can flow uphill =P
Supposedly there are only three places in the world where this happens, though in the quick search I did I could not find their names (several youtube videos and mentions though).
Fact remains that nature has stuff far more strange than what we can imagine =)

02-06-2010, 09:05 AM
Nobody expects the River Police! Their chief weapon is gravity. And topography.

Nobody expects the River Police! Their twin weapons are gravity, topography, and a fierce determination to enforce physical law.

AH, bugger.

02-06-2010, 09:14 AM
I spent a few mins (maybe 10) looking through google for something about water flowing uphill, and it's difficult to find something that isn't scientists testing in laboratories, optical illusion, or people arguing about it and referring to the fact that it can happen but not providing direct reference sources :)

Perhaps I'll try later when i'm looking for something to do that isn't time critical :)

(i'm not disbelieving, just annoyed at how long it's taking me to not find anything, usually i'm pretty good with the searches)

waldronate: brilliant!!

02-06-2010, 09:40 AM
please .. please not the soft cushion!! I confess!

02-06-2010, 10:00 AM
The only example that I can say I have seen, is the "reversing falls" off the Bay of Fundy. The reason that the water "goes uphill" is that at low tide the water level is sufficiently lower to allow a long stretch of the river to flow down hill before hitting the bay. When the tide comes back in, the water level of the bay is so much higher that the above mentioned stretch of river is now below the water level. The reversing part is when the tide comes in and flows up the soon to be submerged part of the river. It still follows the water flows down hill rule = The higher water of the bay flows into the lower river bed. A contradiction, but hey, I believe that is what is called a tidal bore (I might be wrong about the name though).

Mark Oliva
02-06-2010, 11:16 AM
if your world has it's own rules, i think the call at that point is to ensure that those rules are followed consistently throughout that world. Consistent internal logic is important to the believability, which in my case at least, adds to the enjoyment.

I agree completely. On both points.

02-06-2010, 10:24 PM
I think there is a river in Cambodia that flows in reverse during certain times of the year... flooding backflows it somehow... not sure the process...

ah Google, you answer my call again:

"The Tnl Sap is a shallow lake in western Cambodia which is part of the Mekong River system. It is the largest lake of Southeast Asia and is fed by numerous streams. During the dry season it drains by the Tnl Sap River southeast to the Mekong River. During the wet monsoon season of June to November, the high waters of the Mekong River reverse the flow of the Tnl Sab River and increase the size of the lake from 2,600 to 10,400 sq km (about 1,000 to 4,020 sq mi). When the high waters of the Mekong River recede, the flow reverses. This natural mechanism provides a unique and important balance to the Mekong River down stream of the lake and ensures a flow of fresh water during the dry season into the Mekong delta in Vietnam which buffers the intrusion of salt water from the South China Sea into the rich agricultural lands of the delta."

02-07-2010, 01:16 AM
Rivers can flow in reverse, but typically only because the water at the mouth of the river becomes lower than the outside ocean, typically due to tides. Water then flows downhill from the ocean to the (now lower) river basin.

The only place that water will actually flow uphill against the flow of gravity is at something called the hydraulic jump. If you turn on the faucet at your sink and watch the water hit the bottom, you'll see the water form a flat disk around the place where the flow hits the basin. At the edges of the disk is a little jump where the flow gets slow enough to transition from the smooth laminar flow of the disk to the turbulent flow of the outer area. This phenomenon can be several feet high for large-volume, fast-flowing areas such as the outflow of a dam pillway. Other than that you'll not see water flow uphill in our world. You may see bits of water flow into a container that's lifted up until the water flows out at a higher level (a pump), but otherwise no.

02-07-2010, 05:29 PM
Waldronate> As a physics chemistry nerd...

Water can flow up ONLY if:
The water will move to a lower potential energy.
Will require minimal energy to go "up" first. (Minimal is massively subjective but unlikely to be found outside a kitchen sink or a syphon)
Will also result in the net increase of entropy.

Or in terms of something the size of a river... I wanna see the science because I doubt it will stack up.

02-07-2010, 07:36 PM
Or in terms of something the size of a river... I wanna see the science because I doubt it will stack up.

http://en.wikipedia.org/wiki/Hydraulic_jump has a lengthy discussion on the topic.

02-07-2010, 08:12 PM
Waldronate: All over the hydraulic jump concept. That's just dandy... but water flowing genuinely "up hill"... that's what I want to see people try explain the science to me for why their river goes where it does... and "Wizards done it" ain't a good answer. I might settle for "The God of Rivers did it, to show he awesome, and slightly chaotic"

02-07-2010, 08:21 PM
Everything I stated was related to water flowing downhill. Water flowing to a higher elevation requires either an input of energy (typically in the form of a pump; see the fleming hydro-ram as an example of moving a small volume of water up a gravitational gradient using the work of a large volume of flowing water) or a change in the local gravity gradient that makes "downhill" move toward higher elevations. In the first case it takes a huge amount of energy to move large volumes of water; in the second it takes exotic physics and/or magic.