Google ancient sewers or Cloaca Maxima. You'll get what you need.
| 1 person marked this as a favorite. |
When's the last time it rained?
Anywhere from less than ankle deep to ceiling height depending on the amount of rain. Sewers can contain arrangments similar to header tanks to generate water pressure, which washes away the debris and can be combined with stormwater systems.
It is probably highest or even overflowing during a extended period of heavy rain and lowest after the rain has stopped and the water drained away. After a period of relatively dry weather the depth is likely to increase a little because of the sludge that will have built up and not been flushed away.
As deep as you need it to be, for dramatic effect.
Lincoln Hills has the right of it.
In some cases, having them wade chest-deep down some corridor can be a wonderful prelude to disaster. Think of the first Star Wars movie and the trash compactor. Having a sudden deluge of water rushing towards them can be a sudden dramatic moment, forcing them to jump through a side door before certain death reaches them.
Lots of stuff to work with in sewers.
In practical terms, I think that 'ankle deep most of the time' is probably appropriate for 'sewers that are adventure sized'.
The assumption here is that the rest of the space in the tunnel is extra capacity to handle rain flooding (you definitely want that room, since you don't want the water to flood back up- you don't want to be the store that is flooded in sewer water). So simple tunnel systems are probably fairly empty the rest of the time.
If you are dealing with larger tunnels, then things start to edge towards 'an underground canal' (which should have 'small sea monster' depths). Smaller than that, and it is probably just a transitional shaft that empties into the main tunnel, so it likely fills up fairly easily.
|
Let's not forget the architectural aspect of who deep the channels were intended when they were built.
ankle deep seems quite shallow, and doesn't move the actual sewage without proper irrigation. "Knee-high" would be a better guestimate for a sewer system that doesn't rely on rain fall to clear it out.
| 2 people marked this as a favorite. |
I think that when sewers went into tunnels, they knew (or soon found out) that they needed access to clean them out. They also realized rain runoff would be great for doing this.
Rain coming down at 1"/hour is really heavy, and can cause flash floods. While a sewer system doesn't need to handle this amount, handling a lesser amount with overflow during heavy rain would be fine.
Next, we have waste production. Even adding in animals, it just doesn't compare to the amount of rain. So you have to plan for a relatively small amount of effluent entering the system all the time. Sewers soon developed a narrow channel in the middle of the tunnel. This meant a much smaller space for the effluent to fill, and better disposal between rains. It also provided dry areas on the side for workers that had to deal with problems.
With an environment full of fecund fertilizer, and waste scraps of food, a thriving ecology will soon spring up. Assorted mushrooms will help break stuff down, and vermine will thrive on the scraps and limited intrusion from larger prey. Expect oozes, rat swarms, and even worse when you go there. Additionally, for portions in poor repair, you can get deep puddles and mud pits. Even partial collapses, that might become a blockage with the slightest bump.
The main mechanical problems will be smell, sound, and light. The powerful smells here are considered stinky by characters, so they will not want to stay down here. Maybe a -2 cha check penalty until cleaned off. Sound will echo, so will be useless for pinpointing much, although bats [and echolocation spells] will be OK. Again, a -2 penalty to perception in that environment unless handled well [according to the GM]. Light will be the same problem it is elsewhere in dungeons. [Actually, so could sound be considered the same.]
/cevah
In general, the sewers in my games run from ankle to waist-deep. I sometimes put debris beneath the filthy surface as a minor obstruction or a giggle for myself when a player trips over it.