POREFORM
Poreform is an urban surface—an intelligent and flexible system of pores—that absorbs and collects water like skin for a city. Capable of rapid saturation and slow release, the pores of this urban skin are inlets to a new adaptable infrastructure below its surface.
Las Vegas is an arid city that suffers from periods of extreme water scarcity punctuated by destructive flooding in the densest urban areas. The Southern Nevada Water Authority (SNWA), which governs the water resources of the city, continually strains against the outer limits of the available supply in an effort to prevent systematic shortages. Meanwhile, because of Las Vegas’s position in the center of the Las Vegas Valley hydrographic basin, the water infrastructure of the city is incapable of absorbing the 27.1 billion gallons of rainwater that flood the center of Las Vegas every time it rains.
In order to understand the profoundly imbalanced equation between water scarcity and flooding in Las Vegas, it is important to revisit the history of Nevada’s water supply, which is a story of political struggle, exponential urban growth, and environmental vulnerability. In 1922, Nevada signed the Colorado River Compact, which divided up the water available from the Colorado River between the seven states bordering the river according to population and need relative to groundwater resources. At the time, the 200,000 acre-feet (97.7 billion gallons) designated to Nevada seemed more than enough for the sparsely populated state.
As Las Vegas rapidly grew in the decades following the compact, the city developed several risky ways of meeting the growing demand. Water banking with surrounding states became commonplace. The SNWA pays other states to hold and not use their surplus water resources so that Nevada can draw upon those resources in times of shortage. The SNWA has also proposed a series of environmentally and politically controversial pipeline projects to direct groundwater from northern Nevada down to the city of Las Vegas. But funding for these expensive municipal projects came from developers’ fees attached to extensive exurban sprawl, growth that halted abruptly in 2007, leaving the pipelines half-built and unusable.
Figure 1 describes the calculated maneuvering of the SNWA in more detail, and estimates the percentage of Las Vegas’s water supply that is currently “at risk,” being bought on credit without a viable replacement plan. Figure 2 assigns value to this risk based on the billable rates, and collective, debt offset, and extract values given to water by the operations of the SNWA. Water functions as a currency in Las Vegas, but when the true value of that currency is calculated, defined, and compared, a rapidly compounding water debt clearly demonstrates the instability and imbalance of the city’s limited water resources.
Las Vegas loses 60,000 acre-feet of rainfall to the shallow aquifer every year in the form of urban runoff, the result of frequent major flooding. At the same time, the city is spending precious energy pumping water uphill from Lake Mead to the newest suburbs, and from the deeper principal aquifer to offset what is lost to runoff. The SNWA depletes the principal aquifer while the shallow aquifer fills with floodwater in almost equal volume, which results in geological degradation, surface compaction, and increasing seismic instability.
The amount pumped from the principal aquifer is not enough to close the gap between the volume of water that Las Vegas is allotted and the amount that it requires. Return flow credits, a major source of water debt, become increasingly important as the SNWA agrees to return, in the form of treated wastewater, the difference between their allotment and what they actually withdraw.
Meanwhile, Las Vegas floods.
Substantial flood control measures have taken the form of large detention basins in the suburbs surrounding the densest areas of the city (see valley map on previous spread). These basins collect some of the annual floodwater in the valley, but are not designed to exist downtown. In the densest urban neighborhoods, where the percentage of impervious urban surface is high, there is no space for the shallow and sprawling detention basins. Meanwhile, Las Vegas floods.
We ask how, through the capture, control, treatment, and release of floodwater, the debt equation can be rewritten, geological degradation can be slowed, and Las Vegas’s dependence on volatile interstate politics can be reduced.
The proposed network of flood control infrastructure is finely calibrated to absorb specific volumes of floodwater at critical intersections throughout the downtown area. Water flow calculations, municipal documentation, volumetric assumptions, and historical flooding data were used to design a network of absorptivity capable of preventing the destructive floods from becoming commonplace in downtown Las Vegas.
The network is divided into subarea watershed zones, each of which has a “sponge” or a small basin capable of absorbing runoff associated with flooding in the immediate area. These small basins are designed to release the water into the network in a controlled way post-flood; each basin drains into the main collection tank, which is sized to take on the entire floodwater volume during times of peak rainfall.
Each subarea watershed zone has an area and peak rainstorm runoff volume; these variables define the volumetric capacity of the infrastructure located in that zone. The analysis of a subarea watershed surface type and permeability defines the runoff coefficient applied to that zone, which in turn defines the absorptive capacity of the Poreform surface for each location. For example, a densely urban zone that is mostly building and paved surface parking, with little vegetation to naturally absorb water, will require a small volumetric capacity and a highly absorptive surface.
Calculating these variables across downtown Las Vegas provides a new map of the city, one that captures volumetric data and fluid dynamics of specific conditions on an urban scale.
Poreform's bumpy surface texture relieves the hydrostatic pressure of moving water, similar to erosion control methods developed in the 1960's. The radius and size of the texture vary depending on use. The bumps for a walkable surface are almost flat, similar to a cobblestone sidewalk, with small pores. The walkable surface transitions into a large capture basin with strong texture and large, protected pores.
The fabric formwork with integrated channels and pores is intelligently fabricated for volumetric and absorptive capacities calibrated for each project site. Poreform maximizes the collection area and provides covered channels for water to travel without evaporation, collecting via underground basins and existing water pipes.
Acknowledgements
Caitlin GK Taylor | Amy Mielke - co-founders of WPP
Keller Easterling - professor at Yale School of Architecture