Visualizing Urban Hidrology: The Design of a Wet Surface

Underground imagination

Within his research about water supply and sewers, the geographer Matthew Gandy includes photographs taken in 1864-65 by Félix Nadar, the first images of the recently built Paris sewers.¹ The photographs contributed powerfully to a transformation in the way the city was seen and understood. Parisians discovered a new and amazing world beneath their streets, the imaginary map of the city integrating verticality. Gandy used Rosalind Williams words to emphasize “the poignancy of the vertical axis to our understanding of the cultural appropriation of urban technologies, since the subterranean environment is not only a technological construct, but also ‘a mental landscape, a social terrain, and an ideological map.’”

Likewise, the recent publication of the photographic report on Los Angeles’ original subway tunnels reveals another layer of depth to the complex city’s surface, formed by dwellings, front lawns and freeways. The tunnels are added to oil drillings, quarries and excavations, seismic faults and big scale spreading the ground for local aquifer recharge, and developing a wider thickness of urban imagination.

Water continuities

Water flow through infrastructures imposes its necessary geometry and connects body and landscape, domestic interiors and public spaces with distant territories whose runoff is collected for the city. Simultaneously, urban rainwater and sewage disappear from the urban space through drains, working as a vector for disposal of waste from the urban metabolism. Pipes, dams and reservoirs build invisible links of territorial scale and draw the extension of the city’s ecological frontier, preserving upstream land from development to ensure runoff quality and polluting water bodies that receive the effluent downstream.

Those pipes intertwine with territorial drainage lines to produce a new geography, a flow of water integrating the city with its water basin. The continuity of watercourses, streams and dry riverbeds forms a delicate yet relevant net of lines that goes through the multiple layer moiré that forms the urban thickness.

Among the energy fields that explain water movement in the biosphere, two of them are the most relevant and linked with management: the one related to physical hydraulic power (measurable according to mass and height over the sea level) and the one related to chemical state (measurable by its composition and solution capacity). Vertical movement, due to evaporation by solar radiation, raises the water and removes dissolved substances. All the water states describe a potential energy field, one that starts with rain and descends to the sea, where it reaches its maximum entropy level. These movements, going through layers and connecting ecosystems, activate an enormous variety of processes as they go by.

Hydrologic palimpsest

Urban construction usually works as a landscape desertification process. Ground surface is paved and soils cannot retain rainwater that disappears very quickly from the environment, turning it dry and arid. Local watersheds lose their performance as invisible underground pipes manage runoff. Only occasional puddles, the result of system failures, enrich urban space with shine and reflection. However, under this impervious surface, thousands of cubic meters of diverse kinds of waters move through the soil and interweave infrastructures and living systems to give rise to a particular phreatic, one tat transforms the regional scale of aquatic dynamics. The underground is the amalgamation of all the externalization of urbanization.

Overlapping cartographies from different periods of a settlement enable another approach to the understanding of urban hydrology. Urban patterns, street directions and topography acquire significance from the drainage lines prior to the sewers’ construction. Within historical centers, the transformation of the natural features during urban consolidation has been softer, and so the original topography and soil qualities normally remain. Waterways have defined and conditioned the urban fabric, interweaving with and within it. They have lasted as linear voids until today, sometimes transformed into traffic roads or freeways.

It is interesting to note how the toponymy has fixed through words different states of the urban nature, in which water was part of the public realm. Names such as Ribera de Curtidores, in Madrid, or La Ciénaga Boulevard in Los Angeles, openly refer to hydrology conditions. Blue Road in Drachten, Holland, a project by artist Henk Hofstra, depicts at real scale this palimpsest. The blue line marks along 1,000 meters the location of an historical channel, where a road can be currently found.

Banyoles is a town located at the shore of the biggest natural lake in the Iberian Peninsula. Traditionally, water channels from the lake went through the town center to irrigate urban orchards and backyard gardens. In the course of time, as orchards disappeared, the channels were progressively covered and used as sewers, losing the relationship of urban space with its surroundings by means of the water flow. The recently-built renovation project by MiAS Arquitectes reclaims pedestrian and water circulation through the city center. Furrows sculpted in the surface of the new stone pavement give form to a water glide. The irrigation system is now intermittently uncovered and eventually it opens into bigger sections, where children can play as if they in front of the aforementioned puddle.

At metropolitan scale, the plan to restore London’s lost waterways pursues the same aim. The project’s website shows an amazing interactive map of the local watersheds and the river Thames’ tributaries that now flow in pipes under the surface. The plan includes multiple strategies within the whole metropolitan area to restore surface drains and waterways, turning them into a continuous system of outdoor public spaces and enabling water to reactivate ground and air qualities.

By understanding the possibilities of ground surface morphology from the layout of local streams, a richer imagination of urban space emerges, pointing out potential transformations to retain and visualize the enormous patrimony of local water and humidity that rain and runoff are. By watching gravity-led water movement, we can identify foldings and ways defined by topography, and concavities that produce natural lamination. It also shows where spontaneous green could appear as a new “riparian vegetation.” Furthermore, opening underground pipes also activates vertical movements; water infiltrates the soil and nurtures autochthonous vegetation or evaporates into the air.

As David Gissen suggests, this approach can be framed into “a peculiar contemporary moment in which “reconstruction” is the modus operandi for politicized forms of environmentalism” and recover hydraulic performance of the traditional city “marking an engagement or partial reconstruction of the city’s now-irrecoverable earlier form.” Hydrologic conditions have evolved as a part of the gradual construction of urban environment. Water’s quality, volume and frequency patterns are different. Water tables have moved away from surfaces and enormous volumes of supplied water through the underground.

Marginal nature

This proposition for public space implies considering rainwater and runoff as an asset for the city. Air pollution and pavement dirt (which include all manner of material resulting from urban metabolism) are swept away by water, very far away from idealistic paradigms of an urban nature, yet closer to the magic and synthetic carpet of delirious New York, or the corrupted biotopes of François Roche. The toughness of the urban environment requires the design of an optimized and technical nature, according to the water we have. Growing Water, a proposal by UrbanLab, envisions the transformation of the Chicago city center into a big treatment machine. Linear eco-boulevards, integrated into an urban grid, operate as a decentralized infrastructure. All the sewage and rainwater treated as it flows through these lines to enable its re-use or its return to Lake Michigan, from where the city’s supply starts. These landscape strips go from the water basin border to the lakeshore. The treatment is made via microorganisms, plants and fish: hydroponic systems and ecological processes for sewage and wetlands as low energy filters for rainwater.

By integrating urban form, hydrological dynamics, overlapping public space and infrastructure, a project of is created of a continuous net of outdoor spaces with new attributes: visualizing systems that support urban life and recover “the productive surface” of the city. Mirko Zardini has emphasized the relevance of the asphalt in the transformation of the urban environment, taking away dust, mud and puddles, but this synthetic carpet is capable of much more. To involve the water flow and evaporation in the design of urban surface would make possible the production of environments and different sensorial conditions. Besides energy efficiency, it would intensify somatic experience and create spatial effects and interferences with the numerous physical, environmental and thermodynamic phenomena that take place around us.