THE EFFECT OF ANCHORED LARGE WOODY DEBRIS ON BEACH MORPHOLOGY: A PHYSICAL MODEL STUDY

Abstract

As the demand for nature-based coastal protection methods increases globally, there remains a stringent need to develop evidence-based design guidance for many of these methods and techniques. Anchored Large Woody Debris (LWD) has been used as an economical method of coastal protection for several decades and has, more recently, gained notoriety as a nature-based approach. Existing design guidance, however, is both limited and not significantly rooted in academic research. This paper presents results from the first experimental study related to coastal protection using LWD. Gravel beach response to various LWD configurations were tested at a large scale based on site characteristics and LWD design characteristics made by the authors during the previous field investigation phase of this research project. Tests were also conducted to assess experiment repeatability, sensitivity to test duration, sensitivity to wave height, wave period, and relative water level, and influence of log roughness. The LWD placement elevation relative to the still water level was found to be strongly linked to the beach morphological response and a theoretical relationship was developed between LWD elevation and sediment volume change. LWD design configurations which included LWD below the still water level, such as the Benched configuration, were found to be most effective at stabilizing the beach profile. To realize potential benefits of coastal protection using LWD, significant additional research is needed on the topic, including studies focused on how to best anchor LWD structures and a wider variety of parameters (hydrodynamic conditions and placement techniques).