Rivers trapped under cities

Rzeki uwięzione pod miastami

Among the numerous ecosystem services provided by rivers that determined the establishment of cities along them, in the 19th century. Their function as a receiver of wastewater has become particularly important. With the industrial revolution increasing the assortment of wastewater, but also driving urbanization, the volume of wastewater has increased so much that it has exceeded the self-purification capacity of rivers, putting the remaining services in question. Contaminated rivers ceased to be a source of drinking water, a place for fishing or recreation, and sometimes it was impossible to use them even for industrial water or aggregate extraction.

Losing the ability to provide certain services is one thing, but polluted rivers are also becoming a cause of serious problems – aesthetic and health. Turn of the 19th and 20th centuries. was also the heyday of the hygiene and microbiology movements, and thus a growing awareness of the role of water in the transmission of germs. These problems were compounded during floods, when polluted rivers overflowed, increasing the epidemiological threat. Meanwhile, it was already known in ancient Rome that a canal draining polluted water does not have to be uncovered at all, and unsightly sewage can be hidden under the surface. Hence, in many cities the idea of not only building underground sewage and water supply networks, but also covering natural streams and even rivers has emerged.

In fact, these ideas are as old as the construction of irrigation systems themselves, for irrigation, drainage and sewage disposal. The period of the Industrial Revolution was conducive to their wider implementation. This was done in metropolises (for example, the Senne River was piped in Brussels), but also in quite small towns at the time (in Rzeszow, a section of the Mikoska River was diverted underground). The same was done with the seven Oslo streams or the streams of the mining and industrial basins flowing into the Ruhr, Emscher or Klodnica.

In Warsaw, the Drna, Zurawka, Sadurka, Belczarska, Rudawka and a couple of others were put into the sewer system. Some of them have no trace left on the surface, while others have only street names, such as Dunaj or Nalewki. Several have been piped only partially, and remnants are still floating on the surface. An example is the Sadurka, which was renamed the Sluzewiecki Creek after such a treatment. The rivers and open canals on the outskirts of Warsaw, such as the Wilanowka or the Młociński Canal (today, by the way, also usually unnoticeable because it has dried up), as well as the Vistula, too large for such an operation, have been preserved as free-flowing.

Incorporating streams into the sewer system not only had a sanitary dimension, but also involved draining land that could be used for development. Today, on hydrographic maps of Warsaw or other cities, one can see unnaturally large patches devoid of watercourses. In places, short, detached fragments are also visible, indistinguishable on a map from moats or elongated pools. Such a system of watercourses flowing on the surface and every now and then disappearing underground resembles a karst system. Streams flow into sewer gullies as if they were ponors and flow out as if they were vents. Given the extension of the term karst to include thermokras, or the phenomenon of the intermingling of surface and groundwater in zones of perennial permafrost, one might be tempted to use a neologism like urbanokras or betonokras (although some of the older drains are ceramic rather than concrete). Or perhaps technocras, in the likeness of the name of technosol-type soil.

Sewer builders did not always take care to document the process, but today such sites are being reconstructed. The course of some remnant streams, nowadays often filled with water only after major rainfall, can not infrequently be linked to a map of storm or sanitary sewers. This is particularly evident in the case of Warsaw’s Sadurka, whose longest piped section runs under the apron of Chopin Airport, and which has several concrete “ponors” and “vents” earlier, in the Ochota and Włochy districts. Rudawka, which is located further north, looks similar. In turn, the outlet of storm sewers into the Vistula near the Czerniakowski Headland in Warsaw is indicated as the contemporary outlet of the Zurawka River.

Such reconstructions are being carried out by representatives of urban studies, a thriving field of science, more social than physical or engineering. Their result was an exhibition titled Let them flow! Other Rivers of the Exhibition, held in early 2022. At the Wola Museum in Warsaw. The names of Warsaw’s now unseen rivers have joined the post of the Sisters of Rivers, a cultural initiative aimed at renewing the relationship between people and rivers. One of her actions was a walking float, or walk, along the streets under which the remnants of the Drna flow. One of the demands of this community is to unearth the walled rivers of Warsaw.

Although representatives of Warsaw’s hydrobiology community were involved in the initiative, in addition to social activists, it sounds unrealistic. Contrary to appearances, however, it is not completely detached from reality. Such measures are already being taken. An iconic example is Seoul’s Cheonggyecheon Creek. The Japanese occupiers had already set about covering it, but the project was not finally realized until 1958-1976, when a downtown artery was let loose over it. A quarter century later, the situation was reversed. The street was removed and the restored boulevards were surrounded by vegetation. Today it is a symbol of nature restoration (naturalists are defensive about calling such restoration efforts – it is still an urban canal surrounded by urban landscaping, not a natural stream among riparian forests), an action for the sustainability of urban transportation, improvement of the microclimate, and in general an example of the success of modern urban activism.

It is a symbol that can shock with its momentum. Meanwhile, there are much closer examples of softer restaurants. In Oslo, the Hovinbakken creek has been partially exposed. Partly, because while the elimination of several streets is conceivable, it is hard to expect the demolition of buildings. In some places, along the uncovered creek, parks have been created with ponds populated by ducks or barnacles. In others, the trough runs along the streets, and the planting is in the nature of a macrophytic sewage treatment plant. Such activities as much as possible can be attempted to be repeated in Warsaw.

The revitalization of the Ruhr and Emscher basins, which resemble our Silesian-Danube basin, included the discovery of the Deininghauser Bach stream. The cities in these basins have various problems related to the transition, including social ones, such as the need to ensure the integration of immigrants. The creation of boulevards at the site of the street is now being presented as an important socializing factor for the post-industrial community. Given the activities of the Upper Silesian conurbation, which seeks to present the region in a whole new economic and environmental light, the restoration of the Rawa could be a similar project.

The thing is, such restorations can only be thought of after the reasons why the streams were once piped have been removed. Sanitary water quality in most of the rivers of the wider North has generally improved significantly compared to the state in the 19th and 20th centuries. This was happening at different rates. Two European capitals-Brussels and Warsaw-were just completing their treatment plants a dozen years ago. The European Environment Agency, in reports on urban waters, points to contaminants in the sediments, both historical and new, including pharmaceuticals. Admittedly, there are maps of sewer networks, but sometimes the actual hydrological connections don’t quite agree with them and sanitary sewage ends up in storm drains. The Sluzewiec Creek is less and less often referred to by local residents as the Smrodka River, but it still, once in a while, records spikes in ammonium nitrogen or coliform titer, indicating incidental sanitary pollution. It is also salty, especially after snowy winters.

Leaving the underground sections is a compromise of nature with the needs of the city, but preserves a barrier for aquatic organisms using mainly sight, such as fish. Hydrogeologists also point to another problem. The Sluzewiec Creek or the remnants of the Ore River rarely still pose a flood threat, but as a rule the opposite is true – these streams are drying up. Sections of the Sadurka River, flowing among the allotments above the airport, very often do not flow, but stand, or are even dry. The restored streams will face the same problems that afflict their existing sections today.

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