The Nature GM

We game masters know that combat can be made more interesting by adding terrain elements. We consider different encounters in which terrain would be an important factor, and we settle on a goblin attack made from across a river. We begin to prepare our battle map, and here we pause.

What does a river actually look like?

In this post we will examine the shape of natural rivers and how to incorporate these into your tabletop roleplaying games.

More Than a Water Ribbon

On everyday maps we are accustomed to seeing rivers and streams represented by a blue ribbon that wiggles and curves from one distant point to the next. On our battle maps we have a tendency to do the same: a river is represented by a fat blue line through a flat landscape. The bank of the river is the lip of land just beside the flowing water.

Real rivers are more than just a ribbon of water. Real rivers have three dimensions, and they often have two tiered banks.

The above image is a river from 2-Minute Tabletop, available for purchase here. It is a perfectly serviceable battle map, and a perfectly featureless river. Where are the pools and eddies? Where are the signs of erosion and flooding in a dynamic landscape? If you fall from the bridge, is there any penalty beyond water in your boots?

The above diagram from the Flathead Conservation District illustrates the complex dimensions of a river. We start with the dark blue section, where the water will flow most of the year. This is most likely where the water level is when your players are crossing—see how even the lower bank slopes down some feet to the water. During heavy rains the light blue section will fill up to the bankfull level (when the riverbank is full), and in a severe flood the entire channel from tree to tree might fill with water.

Consider the scale of the water body. Both the battle map and diagram technically illustrate streams rather than rivers. As a rough guideline:

• River – wide and deep enough for a boat; must be swum across
• Stream – wide and deep enough for a canoe; can often be waded across
• Creek – too shallow for any watercraft; can possibly be jumped across
• Bayou – a stream in a swamp; contains alligators

A Battle on a Stream

You have been travelling all morning across grassy, rolling hills. About an hour ago you entered a line of trees, and the ground has been sloping steadily downwards. Ahead of you is a stream perhaps 25ft wide, which you must cross. Your party decides to walk along the stream looking for a place where it narrows. You find a point where the stream has been partially blocked with boulders, creating a natural bridge with a pool on the left and a small waterfall on the right. You are halfway across the boulders when an arrow whizzes past your ear. You look up and see a band of goblins on the far bank, firing at you with shortbows. They are 50ft away.

In this scenario the players have several options. Do they continue to cross the stream under fire? Are they able to retaliate? Do they retreat and look for another place to cross? Do they jump into the stream and try to get away, risking the loss of some of their equipment? In normal circumstances I would not require a check to cross the boulders, but when under fire I would ask for a roll to maintain balance, and failure means falling either into the pool or downstream.

Consider how the encounter changes if the players have a sturdy, well-made bridge to cross. Or a slippery, decaying bridge. Or a log. A constructed bridge would most likely span the upper banks, from tree to tree in our diagram. Falling from such a bridge could mean a 20ft drop into a 5ft deep stream, which is too shallow to break the fall.

The goal is to create an encounter which is unique, engaging, and memorable for the players. They will undoubtably remember plummeting into water and being swept downstream, even if they do not later recall the context in which it happened.

Descriptive Details

Where a stream is narrower, it tends to be deeper, faster, and cut steep banks. Where it is wider, it tends to be shallower, slower, and build sloped banks. Streams that pass through cities tend to have artificially deep channels and high banks to prevent flooding.

Streams in mountains tend to have rocky bottoms and cold water. Streams near the coast tend to have muddy bottoms and warmer water. The further downstream you are from the headwaters, the more sediment is in the water due to erosion.

River Beasts

What monsters lurk in a stream should be commensurate with the stream’s size. Some animals that may inspire river monsters include carnivorous fish, sharp-beaked turtles, alligators, venomous water snakes (which swim on top of the water), toxic frogs, giant mosquitos, maybe even a monstrous dragonfly that disorients its prey with a kaleidoscope shimmer of its wings. Wily beavers that build traps to ensnare prey. Aerial predators that strike when prey is waist-deep in a river.

In Closing

Finding real photos of streams (or rivers) in your desired landscape can provide inspiration on how the shape may be relevant to your players. 2-Minute Tabletop also has other maps which are more realistic and interesting, such as this terraced waterfall. The more you detail you give your players to interact with, the more creativity they can display when making character decisions. And that is enjoyable for us all.