Life Cycle Assessment of soil and water bioengineering structures

Nowadays there is a high demand on engineering solutions considering not only technical aspects but also ecological and aesthetic values. Soil and water bioengineering (SWB) is a construction technique that uses biological components for hydraulic and civil engineering solutions. In general it pursues the same objectives as conventional civil engineering structures. In this context SWB techniques are often used as standalone solutions or in combination with conventional engineering structures. Currently, existing assessment methods for SWB structures are evaluating technical and economic aspects. In a modern engineering approach, additionally, environmental impacts should be considered. Therefore, the Institute of Soil Bioengineering and Landscape Construction aims at developing an Environmental Life Cycle Assessment (LCA) model for this special field of soil bioengineering and river restoration. Different studies were carried out to assess the carbon footprint of various SWB structures mainly with the popular impact category Global Warming Potential (GWP). The life cycle itself can be divided into four phases: the product phase, the construction phase, the use phase and the end of life phase. For the presented case studies the system boundary is defined as cradle to gate (until the construction is finished), except for one case study where the use phase is analysed (including the maintenance and conservation work as well as the potential positive effects resulting from the living plants). The results show that SWB construction sites are able to perform better in terms of carbon emissions than conventional construction sites, but they even cause negative effects on the environment. Apart from that, SWB structures are able to compensate emissions from construction by absorbing carbon through growing vegetation in the use stage. Therefore, a holistic approach starting in the planning stage can help to optimize processes throughout the life cycle and to minimize the environmental burdens. The case studies show that the application of an LCA model is not only important in terms of engineering effects but also provides transparency for the responsible planners and stakeholders, by pointing out the total consumption of resources in all phases and components.