Sewers of Torrune

The city of Torrune has a complex and well-designed sewer network, the likes of which is not to be found elsewhere in the Helvandrian League. This is a legacy of past Archons' generous investments in the city's public works (and the role of dwarven engineers in designing many of the same).
Since Torrune is divided into the High City and Low City with the River Helvander running between them, it actually has two separate and unconnected sewer systems, one for each part of the city. The Low City's sewer network is of course physically larger and more extensive, but that of the High City is more sophisticated and often in better repair, since that district's wealthy inhabitants have more money to spend on its upkeep and are generally keen to ensure that foul-smelling waste is efficiently carried away from their grand houses. Fenside lacks anything comparable to either, and the many open gutters carrying sewage down to the river contribute to that quarter's distinctive atmosphere. The situation is of course even less hygenic in Little Maarna and the Shambles.
In both the High and Low Cities, the main elements of the sewers are tunnel-like covered channels running under the street level, fed by drains and chutes from the gutters of the neighborhoods above. They all slope gently down towards the level of the Helvander, so that their contents eventually flow down out of the system and into the river, either directly from the sewer channels or (in the Low City) by first draining into the canals. Some of the Low City's major sewer channels are in fact former canals which ended up having so much waste drain into them that they were covered over and made into parts of the sewer system themselves.
A steady flow of water through the whole system is maintained in order to flush waste through and prevent its accumulation; the continual overflow from the city's spring-fed cisterns and aqueducts is directed into the drains and gutters, or straight into the main sewer channels themselves, to achieve this. Thus the functioning of Torrune's sewers is ultimately possible only because the city is blessed with several perpetually flowing springs on its various hills.
Although Torrune's sewer system today is the largest and most complex the city has ever had, it is also intermingled with the fragmentary remnants of older sewer networks. Some of these date back to the days when Torrune was still ruled by the Duchy of Charagma, before the construction of the current, more sophisticated, system; others date back still further to the days of the Old Empire, or even earlier. The current system incorporates many sections of tunnel that were already in place from these older sewers, but others are long-disused. They may form dead ends branching off from newer tunnels, or maze-like tangles of passageways leading nowhere, hip-deep in filthy stagnant water. Some are bricked up and sealed off, or connected to the current system only by small drains or narrow crevices; others may be partially filled in with earth or rubble. These older sewer tunnels are often deeper than the more recent ones, owing to the slow rise in Torrune's street level as new construction has grown atop old ruins over the course of centuries. Old disused sewer tunnels are most common under the south-central quarters of the Low City, since that is the area that has seen the longest habitation and most frequent reconstruction over Torrune's history.
This complex network of sewer tunnels makes up one part of Torrune's larger under-city.