C+S June 2022 Vol. 8 Issue 6 (web)

Conclusion Many beachfront developments in Southern California are experienc - ing rapid beach erosion and shoreline regression. Coastline and ad - jacent improvements within the Capistrano Bay Community Service District have suffered notable beach damage in recent decades. As storm surges, sea level rise, and increasingly destructive wave action continue, more erosion events are anticipated. Without a permanent, community-wide engineered solution employed, property owners within The District have deployed a range of products and systems to mitigate beach erosion. As the California Coastal Com - mission discourage further use of riprap, property owners within The District have sought other temporary solutions to protect their homes. Of the beach erosion mitigation measures observed within The Dis - trict, the short-term performance, versatility, speed of deployment, longevity, and cost effectiveness of the Muscle Wall product stands out in the Erosion Control Matrix (Table 1). Muscle Wall has proven to be an agile, resilient, and durable shoreline erosion product. Muscle Wall can be rapidly deployed before a storm, and can outperform other short-term beach erosion mitigation solutions in terms of their longev - ity and resistance to degradation and beach pollution. Barriers can be taken down and reused, or remain in place for years at a time with little to no maintenance. Due to its durable, corrosion-resistant LDPE mate - rial, we expect the Muscle Wall barriers to withstand continued use for many years to come or until a more permanent engineered system can be employed. Craig Wright is an Engineering Geologist CMEngNZ (PEngGeol). Craig’s experience in New Zealand and the United States involves per - forming geotechnical consultation, project management, field mapping, fault and landslide investigations, geotechnical hazard analysis, storm - water monitoring, and geotechnical instrumentation installation and monitoring. He provides feasibility studies to advise clients of potential geotechnical hazards and construction constraints of their property.

Figure 7: Partially buried Muscle Wall barriers at The District

Partially buried Muscle Wall barrier

Partially buried first tier of Muscle Wall barrier

unprotected property. This is likely the effects of flanking erosion (also known as end scour). Flanking erosion occurs at the ends of a beach erosion mitigation system or product, where wave energy is reflected laterally along the shore, causing unprotected properties to erode faster. Any beach erosion solution that hardens a portion of the coastline will induce flanking erosion to adjacent properties. We acknowledge that there are many other mitigation measures and products available for temporary mitigation of beach erosion; however, the purpose of this study was to discuss the main mitigation measures observed within The District. Table 1, below, presents a summary matrix showing relative effectiveness of the different countermeasures discussed in this paper with regard to the following considerations. • Longevity – The relative ability of the mitigation measure to provide the intended mitigation through multiple events/seasons. • Durability – The relative ability of the mitigation measure to maintain its shape/position. • Resistance to Degradation – The likeliness of the mitigation measure to bio- or photo-degrade resulting in loss of erosion protection and/or pollution generation. • Initial Value to Cost (V/C) Ratio – The relative value of the initial installation of a mitigation measure divided by the cost of the measure. • On-Going V/C Ratio – the relative value of a mitigation measure divided by the cost of on-going maintenance of the measure.

Table 1: Beach Erosion Mitigation Matrix


June 2022 csengineermag.com

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