The History and Future of Using Vegetation in Construction
The cost and resilience benefits of bioengineering continue to prove that “engineering with nature” deserves greater adoption and implementation, as it has in some fashion for millennia.
By Wendi Goldsmith, CPG, M.SAME
Bioengineering has been practiced for millennia, with documentation in textbooks, design manuals, and in practice. Today, a growing number of high-profile projects further solidify the benefits and versatility of this discipline. Bioengineering consists of embedding vegetation in soil in purposeful arrays for stabilization while plants become established, thus adding increased strength over time. Rooted in traditional methods dating back thousands of years, bioengineering has evolved to include advances in science, analysis and design.
On a localized basis, environmentally sensitive measures have gained preference in recent years, as opposed to “traditional” hard engineering techniques, such as riprap, wire mesh gabions, cement filled bags, retaining walls and other fixed methods. Yet compared to structural measures, bioengineering and other forms of “engineering with nature” remain infrequent. The disparity between readily quantifiable methods of conventional engineering techniques, versus the desire to employ methods that promote long-term functioning of natural systems warrants further attention. In practice, most professional engineers are comfortable relying on inert hard materials, despite the benefits of using natural materials that form living systems. For some, the simplicity of the standard structural approach appeals and dominates selection criteria, despite high lifecycle impacts from structural solutions. Highlighting and documenting the direct link between bioengineering methods and climate mitigation, adaptation and resilience could help engage and equip key decision-makers with necessary information to overcome factors that otherwise impede adoption.
INNOVATION ROOTED IN THE PAST
Bioengineering is seen to some as cutting-edge and technically advancing into new avenues and expressions; to others, it is traditional or even quaint and old-fashioned. This dichotomy is at the core of its adoption, or lack thereof. In ancient times, the use of bioengineering methods helped to overcome the lack of manufacturing and shipping systems by applying live plants primarily from local sources to create and improve landforms and built structures. Modern designs achieve similar results driven not by a lack of options, but by increasing awareness of the environmental costs of manufacturing and shipping, and the numerous benefits of functional vegetation to local ecosystems, regional quality of life and global climate processes. The lifecycle functions and benefits of bioengineering are numerous, and align favorably with sustainability and climate resilience goals.
Riprap versus bioengineering results in different lifecycle impacts.
Projects in many regions of the United States have used bioengineering for sustainable development projects intended to fulfill varied functions for project owners with distinct needs, constraints and preferences. Today’s practice is increasingly based upon sound application of typical bioengineering treatments, though it also incorporates more nuanced variations and innovations that reflect the priorities of the 21st century.
While remaining rooted in tradition and proven performance, the field has evolved to incorporate modern construction materials, improved science related to design specifications, and broader targeted features and benefits for design treatments. The treatments found within the practice of modern bioengineering span familiar and ancient measures—creative, sophisticated, and even whimsical measures, each tapping solar radiation to grow, regenerate and adapt to conditions over time, while contributing soil and watershed health.
Though a focus on concrete, steel and plastic has, from time to time, displaced interest in bioengineering materials and methods, these natural solutions have persisted in use, especially in remote or cash-poor localities.
Given that many designers may not be familiar with bioengineering measures, it is valuable to provide basic definitions and a historical overview of the practice. Etymologically, a host of terms has been used, somewhat interchangeably, to describe similar treatments. Ingenieurbiologie was the term in German, perhaps best translated as "engineered biology" and appeared first in publication in 1851 (Arthur von Kruedener). In recent decades in the English language, many terms have been used, often in search of clarity and differentiation from the fields of biomedical engineering and biotechnology related to pharmaceuticals or genetics. Among the many variations include soil bioengineering, biotechnical stabilization, biogeotechnical engineering, and ecological engineering.
To further explain and refine the scope of the term, additional explanation can be added, such as streambank, shoreline, coastal, and slope bioengineering. Clearly, some potential for confusion exists related to terminology that is connected to genetic engineering, artificial organs, medical devices, and other fields unrelated to the topic of “engineering with nature.”
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The term “bioengineering” encompasses the application of biological elements to a range of engineering applications, and vice versa, applying engineering practices to biological systems both large and small. Vegetation has been used effectively, and with great cost-savings, to manage urban runoff and its non-point source pollutants. Treatment wetlands have a demonstrated track record processing explosives residue, municipal sewage, and more. Conventional engineering techniques (notably riprap and other inert materials) represent solutions to bank stability issues with easily quantifiable responses to applied hydraulic and geotechnical forces. However, consideration of stream, riparian and watershed ecological functions is equally important, and vegetation represents a natural solution.
As the term began to be used in the mid-1800s, it grew with the key engineering activities of the era, namely stabilization of hill slopes, roadways, riverbanks, and drainage channels. In these cases, the emerging analytical and predictive methods of the newly defined practice of civil engineering were being applied to locally available and familiar materials such as timber cribwalls and various arrangements of dormant woody cuttings for contour stabilization and earth fill reinforcement.
Prior to the advent of modern materials such as steel and concrete, vegetation was standard for heavy construction, which occurred mainly for military fortifications (described in 1810 in detailed manuals by William Duane, a friend of Thomas Jefferson). Throughout Europe during World War I, bioengineering measures remained common for construction of steep yet stable walls on which trench warfare depended. While it would be easy to dismiss the various willow fascine, wattle (or claie), and gabion military earthworks common in Europe during this time as rustic improvisations, in fact, they are similar to treatments used throughout the globe. Such measures were rigorously described in annals of bureaucrats and depicted in artwork of ancient Egypt, China and Rome. These measures later spread as standard military engineering practice due to effectiveness and locally adaptability. These applications of engineering used readily available and highly functional biological elements (pliant willow cuttings were a staple, configured into many forms, often combined with other materials). They addressed the crucial needs of the day and built upon traditional practices by drawing upon developments in scientific assessment, conventions of analysis, and standard design. The materials offered physical reinforcement beginning at construction, and typically improved over time as roots grew and added further soil reinforcement. Even when plantings did not survive for long, the short-term root development had the ability to offer significant soil strength improvements through fibrous inclusions that would endure for years.
Historic illustrations depict use of willow branches for fascines, claies (wattles), and gabions to construct stabilized earthworks for trench warfare during World War I.
One notable river management example on the Yellow River in China was commenced over 2,000 years ago where willow reinforced earth was used for bank protection. Many similar practices have been recorded by travelers or in artworks throughout Asia into present times, establishing widespread usage. In the less distant past, one of the most audacious engineering feats of the 19th century relied upon bioengineering techniques. The project involved construction of jetties at the mouth of the Mississippi River to promote the self-scouring action of river flow to allow unimpeded passage of boats through an area plagued by shoaling. James Buchanan Eads, considered a founding father of river engineering, sought to expand on his recent accomplishments designing and building the first bridge to span the Mississippi River north of St. Louis. The bridge had changed major patterns of commerce and Eads sought to tackle the next impediment to movement of goods along the river. He privately funded the construction of jetties, using woven willow mattresses to contain the rock, soil, and sediments of the structures. In what was an early example of a public-private partnership, he agreed to be paid only if the system functioned to allow navigation to depth of 30-ft without dredging. Completed in 1877, Eads’ massive and unorthodox solution indeed did work. He received payment and continued to be paid for the 20-year period of operation during which the Port of New Orleans became the second busiest port in the nation.
While “sustainability” has not been a defined project goal until recently, the practice of bioengineering techniques has served as an applied method for incorporating sustainability into project design since long before such public policy existed.
Though a focus on concrete, steel and plastic has, from time to time, displaced interest in bioengineering materials and methods, these natural solutions have persisted in use, especially in remote or cash-poor localities. Individual advocates have emerged throughout the world at various times to reintroduce the practice of bioengineering to address conservation issues.
At the same time as the dustbowl era, for instance, out in California bioengineering was utilized to introduce effective road building and post-fire reclamation methods using local species as dormant cuttings and planted specimens. Many developing nations today rely on traditional bioengineering methods to guard against riverbank erosion or landslides along roadways.
Eads willow mattress construction, circa 1876. PHOTO COURTESY LOUISIANA STATE MUSEUM
SUSTAINABILITY—AN APPROPRIATE CONSIDERATION
Integrating bioengineering measures into project design can increase sustainability by harnessing the ability of plants to use sunlight to grow, adjust and achieve substantial levels of self-repair. No development process is more natural than photosynthesis. A design process that includes interdisciplinary team members spanning ecology, earth science, engineering, landscape architecture, and related fields will best support effective identification of opportunities, limitations and features for project design. Improved decision frameworks can guide better design as well. Drawing on properly integrated and diverse expertise can allow designers to harness natural processes. Living systems, in turn, can tap positive feedback cycles for landscape features that provide better resilience in the face of increased flood risk due to extreme storms and built-out watersheds. In contrast, many past methods for addressing a range of common design issues create further impacts to natural systems. These impacts often include ongoing resource consumption in the form of construction materials and further energy inputs for operations and maintenance.
In many cases, structures displace or degrade key ecosystem processes needed for quality of life. Useful examples abound for applying vegetation to solve problems that were previously considered the domain of engineered structural and mechanical solutions—whether addressing smaller-scale residential and commercial development or tackling major infrastructure-scale programs; whether undertaking projects in high-tech city centers or developing nations; whether initiating new construction or starting retrofitting and restoration of heavily developed sites.
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Bioengineering as a field merits recognition and wider adoption as a multi-beneficial toolkit to advance sustainable development around the world. While “sustainability” has not been a defined project goal until recently, the practice of bioengineering techniques has served as an applied method for incorporating sustainability into project design since long before such public policy existed.
New federal policies call for addressing climate resilience within agency programs and projects. Bioengineering has previously been applied as a de facto treatment to address climate change adaptation and resilience functions, and is becoming recognized as a potential resource on large scales for reinforcing rivers and coastal areas to enable them to better endure and rebound after increasingly intense storms and other disasters. The primary function of bioengineering treatments is the development of vegetation, which in turn relies on sunlight for energy inputs that drive ongoing growth, regeneration, and self-maintenance. This key function becomes increasingly important in the face of climate change and increased stressors impacting rivers and coastal areas in the form of variability and intensity of rainfall, storm surge and sea level rise. Bioengineered treatments for dune and wetland stabilization have been touted for their performance in the face of major impacts including Hurricane Katrina and Superstorm Sandy. Researchers at the U.S. Army Engineer Research and Development Center are involved in long-term investigation and computational model development to better characterize how vegetation and natural landforms function when stressed by storm damage and other factors. Ultimately, models could allow for improved design capability—including the ability to address large-scale areas and lengthy timelines of geomorphic change, sea level rise and ecological response.
An inherently “green” solution set can solve many standard engineering problems, while simultaneously addressing local biodiversity, watershed scale stability, regional quality of life, and global climate and carbon cycle balance. Compared to concrete structures that have a finite design life of typically 50 years, and which emit large carbon emissions during manufacturing and shipping, vegetation can typically be harvested locally and renewably, and absorb carbon over a nearly endless design life.
In stark contrast to structural materials, bioengineering treatments mitigate climate change through their beneficial contributions to carbon sequestration. Many parties have sought to restrict greenhouse gas emissions from fossil fuels, or to inject carbon dioxide emissions into deep geologic formations for permanent storage, thus avoiding climate impacts. An alternative carbon capture and sequestration approach could pay for itself by delivering benefits such as stabilization and resilience, as well as pollutant removal. Bioengineering measures could well prove to be more attainable than other technologies currently under evaluation.
Many of these bioengineering principles were applied for the Greater New Orleans Hurricane and Storm Damage Risk Reduction System of the post-Katrina New Orleans. While the system features many hardened conventional structures, it additionally incorporates reinforced constructed dunes, nourished beaches, and restored salt and brackish marshes, among other bioengineered measures. The U.S. Army Corps of Engineers tapped the collective knowledge and decision process of researchers, design professionals, construction experts, and international advisors in order to formulate and execute the $14 billion program.
The inclusion of bioengineering measures in the largest climate resilient public infrastructure project in U.S. history suggests that bioengineering is a technology whose time has arrived. The direct compatibility between bioengineering practice and climate change mitigation, adaptation and resilience makes it a sound choice to address increasing public and private priorities to develop and deploy effective and financially sound solutions.