By Rachel Krasna and Andrew Rella, Ph.D.
Ports are at the forefront of environmental challenges associated with climate change and coastal development. To adapt and build climate-resilient infrastructure, ports require innovative technologies and novel design considerations beyond the mandatory industry standards. In recent years, there has been a growing interest among coastal stakeholders and engineers to integrate nature-based structural solutions into the designs of port infrastructure — exploring how natural processes and engineered technology can provide solutions to reduce a port’s ecological footprint.
In 2019, under the framework of the Blue Economy Incubator Program, the Port of San Diego approved a pilot project with ECOncrete, an ecological engineering company developing bio-enhancing concrete for concrete-based coastal and marine infrastructure. The main objective of the project was to develop an approach to address the ecological enhancement of the riprap armor protecting Harbor Island adjacent to the San Diego International Airport, with the primary goal of creating well-defined local ecosystems that mimic natural rock pools and provide favorable environments for abundant and rich biodiversity.
Harbor Island is a human-made peninsula created in the early 1960s with material collected during harbor dredging. The 2 mi long island sits directly across Harbor Drive from the airport and contains a handful of low- and mid-rise buildings and a road running from one end to the other, which connects it to the mainland. The Port of San Diego owns the land and provides municipal services.
The first constructive ecological concrete armor unit — known as CoastaLock — was developed through the combined work of a multidisciplinary team of marine biologists, industrial designers, and coastal engineers. The units measure approximately 5.4 ft long, 5 ft deep, and 4.1 ft high. A central, stepped void within each unit provides space for marine life habitats to develop, and the interlocking system allows the units to be placed in various orientations.
This interlocking, multidirectional unit system was designed to meet the structural and coastal engineering requirements necessary for it to be incorporated into breakwaters, ripraps, and revetments as an alternative or complement to traditional armor layers for shoreline stabilization. Significantly, while meeting these requirements, it also provides ecological benefits by promoting marine organisms and the restoration of local ecosystems as well as raising awareness of the importance of engineers’ consideration of native marine habitats when designing any form of coastal and marine infrastructure.
The design of the CL units and interlocking system considered operational aspects such as lifting, handling, storing, transporting, installing, and stabilizing the mass-concrete units so that they could be maneuvered and installed using typical shoreline protection methods and equipment.
The design assumptions were assessed through physical modeling in collaboration with the Hydraulic Engineering Laboratory of the Delft University of Technology, where 2D physical model testing investigated the hydraulic stability of the CL units. With the inclusion of water-retaining elements and the multidirectional design that caters to the creation of various habitats, the units encourage the addition of crucial habitats usually missing from coastal and marine infrastructure. Through mimicking naturally occurring tidal pools, caves, and overhangs with the multidirectional design, the system enables the local species composition to grow toward a richer, diverse, and natural community with a lower ratio of invasive to native species when compared with traditional riprap.
In March 2021, ECOncrete completed the first CL installation along Harbor Island at the port, where the former waterfront riprap armor protection was offering limited habitat value.
The installation included 74 units with finished armoring extended along two 75 ft long sections of the shoreline in four rows. The upper three rows were placed to mimic natural tide pools while the lower row was rotated sideways to create cave habitats. The port and ECOncrete monitored the project for two years to evaluate the system’s ecological and structural performance.
That monitoring found increasing trends of species richness compared with the adjacent 60-300 kg of riprap stone that has been in place for decades and were considered as control rocks. In addition, significantly higher biomass accumulation was found on the CL units compared with the control rocks, both for organic and inorganic matter.
The CL cavities constitute a newly introduced water-retaining habitat that was missing at the riprap rocks. This new habitat enables the recruitment of multiple species of algae and invertebrates, resulting in the establishment of a diverse marine community. The CL featured a thriving network of species such as ecosystem engineers, indicator species, and keystone species, which all create ecological enhancements.
Beyond their physical design, the units were produced using ECOncrete’s admix, texture agents, form liners, and molds. The technology uses principles of ecological engineering and nature-inclusive design to increase the structural and ecological properties of coastal and marine infrastructure. The combination of three key elements — concrete composition, surface texture, and macro design — results in coastal and marine infrastructure products that mimic natural marine habitats, supporting a strong and healthier ecosystem and decreasing the negative effect of coastal development. This serves as evidence that with the use of innovative technologies and materials, designers can adapt designs and infrastructures to the current climate change challenges.
This project was recognized by the San Diego Section of ASCE and awarded the 2022 Outstanding Airports and Ports Project award, the Design Educates Award, and the 2022 Energy Globe National Award.
Rachel Krasna is the environmental policy specialist and Andrew Rella, Ph.D., is the technical director of business development for New York City-based ECOncrete.
This article is available in partnership with the ASCE INSPIRE 2023 conference (Arlington, Virginia, Nov. 16-18), where Jorge Gutierrez Martinez, the global head of engineering for ECOncrete will present on the topic as part of a panel on nature-based solutions. Register for the conference today.
This article is published by Civil Engineering Online.