Sci-Fi Manholes & Underground Sewer Tours
Just west of Frankfurt, Germany; the city of Wiesbaden holds some fascinating underground sewer history that has provided unique public access and insight into the underground word of wastewater over the last century. Situated on the northern bank of the Rhine River, engineers in Wiesbaden designed a network of underground canals between 1900 and 1907 to better service the city’s population. The large basket-handle shaped tunnels allowed for entry and traversing many parts of the underground flow path as wastewater made its way south towards a rake and sand trap treatment point before the Rhine River discharge 100m into the main Rhine channel.
Figure 1– Underground tours have been popular since construction. [Image by Patrick-Emil Zörnern](a)
A Combined Wastewater Network
To assist flow and flushing within the underground pipe system, the ‘Salzbachkanal’ was designed with controlled fresh surface water intakes from numerous local streams (or ‘bach’ in German) during low flow conditions. To reduce the frequency of blockages during low flow and on the shallow grades within the system, a higher-level storage tank supplied by stream flow was available to certain parts of the system. This meant that in only very rare circumstances would potable water be required for flushing. Part of the operation and maintenance of the system also meant that sewer workers would descend into the tunnels and clean the brick inverts with brushes and brooms.
A series of weirs were designed so in the event of high flow within the canal due to wet weather, the combined flow would spill to local rivers and streams once 5 times dry weather flow was reached, bypassing the treatment point.
Figure 2 – Confluence point of the Schwarzback/Rambach and Kesselbach/Wellritzbach canals. [Martin Kraft, MKr09174 Salzbachkanal (Wiesbaden), Cropped, CC BY-SA 4.0]
The canal was even used to dispose of street snow that was collected and disposed through snow-chutes at strategic locations above the canal. The large canal cross-section and warmer wastewater flow meant the snow melted quickly and flowed onwards downstream.
Located up to 7 metres below street level, the Salzbach Canal includes the famous basket-handle brick design which remains in mostly excellent condition to this day. This is in large part to its careful construction and material choice with a combination of clinker brick wall and hard-fired glazed stone. In addition to the more photographed parts of the network, there are concrete egg-shaped and circular glassed stoneware sections.
Figure 3 – Steep section of basket-handle canal cross section. [Image by Patrick-Emil Zörnern](
A Unique Entry Point
This must be one of the most unique manhole covers we have seen. If there are other locations that use this six-piece triangular outward opening design with spiral staircase, we would love to see some photos. The local waste authority (ELW) has run 25 person tours of this historic underground network in the past, it isn’t clear if these tours are still available.
Figure 4 – One of the entry points to the Salzbachkanal [Image by Brül](c)
About the Author
Mark Lee is the Business Development Manager (Aus/Nz) at VAPAR and a former Senior Asset Engineer who has spent more than a decade managing the asset lifecycle of infrastructure. He has extensive experience managing pipeline networks, including design, construction, condition assessment and decommissioning.
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