Material Matters
Using Vitrified Clay Pipes to return the LA River to its Native Floodplain
After a series of disastrous floods in the 1930s, the United States Army Corps of Engineers (USACE) decided the Los Angeles River needed to be tamed. They encased the river bed in concrete, finalizing an immovable path for the river that, prior to that point, would periodically overflow its banks during the wet season. This spread alluvial sediment that replenished the floodplain with fertile soil, a part of the natural cycle that would regenerate the habitat of the native plants and animal inhabitants of the LA Basin.
The LA River is a combination of treated wastewater, stormwater from urban runoff, and small amounts of groundwater, and the river channel carries this collected water directly out to sea. Bending the River captures that water instead, redirecting it to Metabolic Studio, where it will be treated and cleansed, and redirected to irrigate Los Angeles State Historic Park.
In 2019, after five years spent designing and securing the necessary permits and permissions for the Bending the River project, Lauren Bon and her team finally cut into the LA River concrete. They opened up the concrete jacket of the river to install the pipes and grate needed to capture the river water and carry it to Metabolic Studio.
Bon had designed a series of triangular cuts in the jacket of the river, covering a surface large enough to accommodate the trench for 300 feet of pipe. Once the cuts were measured and marked, the construction team used chainsaws and circular saws to outline these equilateral triangles, each side eight feet long. Triangles were an aesthetic choice but also made the concrete sections more aerodynamic and easier to remove, as this barrier was transformed into building blocks for a large-scale sculptural installation. Traditional construction practices would have demolished the concrete but for this project, the material was salvaged for reuse. This emphasis on permaculture, a closed-loop system where nothing is wasted, was an essential part of the work.
The top surface of these large cement triangles is smooth, but the underside had been poured on top of the pebbled floodplain almost one hundred years ago. That concrete is rough with the texture of encased sand and rocks that originally provided a bed for the concrete, and the concrete shows their imprint. These triangular cuts were designed to protect this historical material as it was removed - and to transform it into both monument and memento.
As the first triangle was lifted however, Bon discovered something incredible. Over the life cycle of the concretized river, the ground underneath had shifted, making space for a new river - pristine groundwater flowed freely underneath the concrete.
The project engineers had drawn up Bending the River’s blueprints using standard construction materials. The pipes intended to carry the water from the intake valve in the river to Metabolic Studio were made of high-density polyethylene (HDPE), regularly used for plumbing and sewage pipes. It is light, inexpensive and easy to work with, but it’s a petroleum-based product. Once she saw the groundwater river, Lauren refused to introduce plastic into this crystal clear water and the natural system that they discovered.
The engineers explained that HDPE pipes are the standard option - they’re accessible and cost effective, and adaptable to different flow levels and conditions. Those considerations might make sense for some of the engineers’ other projects, but for Metabolic Studio, the discovery of clean groundwater challenged these conventional construction practices. Bending the River is transformational infrastructure, based on the principles of adaptive reuse - the construction on this project could not be business as usual. Lauren halted to construction in order to explore other options.
Extensive research on alternative construction materials led to California-based Gladding McBean. Founded on the site of a large clay deposit outside of Sacramento, the heritage brand that has been making clay sewage pipes since 1875. Not only are clay pipes an environmentally conscious option, made of natural materials, but they last twice as long as plastic pipes, further reducing their environmental footprint.
Since Bending the River had already applied for and received all the necessary permits for construction, changing the pipe material required an amendment to one of the hardest permits to secure, the 408 permit from the US Army Corps of Engineers. The USACE is responsible for maintaining and improving civil works and national waterways and harbors, and while Los Angeles County and the City of Los Angeles own the LA River, the USACE oversees a large stretch of the 52-mile waterway. A 408 permit is required for any material alteration to USACE projects.
Small alterations to approved 408 permit plans can be handled locally, but larger alternations need approval from USACE headquarters. Concrete was re-poured to close up the river again, and the laborious process of updating the permit with the USACE began.
In 2021, two years later, the new plans were finally approved and construction once again began in earnest, using Gladding McBean vitrified clay pipes. Vitrification refers to heating a substance until its chemical structure liquifies. As it cools, it takes on a glass-like structure. Clay doesn’t always achieve true vitrification, but it dramatically increases in density with reduced porosity, becoming harder, more durable and effectively watertight. Fired clay erodes the same way rock does - slowly, over eons and it returns to the small rock particles that made up the clay dust in the first place.
The construction crew, however, needed to learn how to work with this new material that was both more durable and more fragile than the PVC they were accustomed to. It is much heavier to maneuver, and it requires a different method of setting the pipes in place and connecting them securely. Vitrified clay pipes are connected by a bell on one end, and a spigot on the other. The bell end is slightly flared with a lip, to allow the spigot to nestle securely inside the bell.
Originally mortar - the material that joins bricks together in building construction - was used to create a tight seal between two pieces, but that meant the pipes were locked together and didn’t allow for any subterranean movement. After the Clean Air Act passed, clay pipe manufacturers began using a ring of urethane on both the inside lip of the bell end and the exterior of the spigot. Urethane is firm but with some give, so a series of pipes connected with urethane seals can adjust and shift with the earth, while still remaining leak-proof and secure.
Switching materials was an illuminating moment for the construction team, and drove home the “why” of the project. Construction processes are optimized for efficiency, which is often seen as in opposition to more sustainable construction methods. This project however, challenges how we determine “cost”. While this delay didn’t fit into a conventional idea of efficiency, it was in pursuit of project integrity. How can you build a regenerative water project when that project is damaging to the water it is supposed to protect?
This integrity of vision effectively illustrated to the project team - assembled from traditional construction crews - why the project was important in the first place. This forced slow-down, and the reassessment of standard materials required for traditional construction, signaled a holistic, big-picture realignment of a well-established industrial process. While Bending the River is a constructed piece of infrastructure, the fired clay presents a remarkable contrast to the petroleum-based HPDE. This reorientation created precedent, and a whole team that can spread the message that it doesn’t need to be business as usual.
