Concrete Cloth Stormwater Infrastructure
Concrete Cloth Stormwater Infrastructure
Concrete Cloth Stormwater Infrastructure
Concrete Cloth Stormwater Infrastructure
Concrete Cloth Stormwater Infrastructure
Concrete Cloth Stormwater Infrastructure

San Luis Obispo, CA
Concrete Cloth™: Stormwater Infrastructure

Challenge

After years of heavy drought in the Pacific Coast town of San Luis Obispo, California, an anticipated El Niño season posed a significant threat to the city’s stormwater infrastructure, main thoroughfares and local wildlife. Due to the lasting drought, the city was already facing flow issues in local storm drains, and needed to carefully rehabilitate them without creating any erosion problems. In addition, maintaining state, county and city storm water quality requirements and minimizing long-term maintenance issues was also an important consideration.

One particular double-barreled 48-inch culvert system – originally designed to convey stormwater from a nearby mountain range – was so impacted with sediment that the system was functioning at about 40 percent of design capacity. Rehabilitation efforts began by cleaning out the lower section of the culvert system and excavating the discharge basin. However, restoring the carrying capacity would cause the flow to impact a four-foot exposed non-vegetated bank at the pipe’s output, creating the possibility of sediment pollution in nearby Laguna Lake, a critical habitat for steelhead trout (Oncorhynchus mykiss).

San Luis Obispo City biologist Freddy Otte worked with Robert Sjoquist, director of Soils Solutions, a local soil reclamation, erosion protection and retention company, to assess cost-effective solutions that would prevent bank failure, yet still be durable enough to withstand droughts and flood conditions. They were also looking for a solution for a point source location to measure water quality and sediment loading.

Most applications fell short of meeting all the requirements. A shotcrete application on the bank would have faced durability issues and quickly lost volume due to the high energy output from the water flow. Similarly, Turf Reinforcement Mats (TRMs) would have needed more time to become secure on the bank in order to withstand even a fraction of the pipes’ anticipated flow. TRMs would have also required constant maintenance and irrigation, which was not feasible due to the drought. A poured in place concrete retaining wall was a more durable option, but would have required extra expense to be engineered and code permitted before installation.

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