Monitoring and evaluation of sand nourishments on an embayed beach exposed to frequent storms in eastern China

Abstract

Beach nourishment is a proved effective protection approach which has been widely used in recent years. An Argus video monitoring system has been set up to monitor morphological changes and effects of continuous nourishments at Dongsha beach, an embayed beach in Zhoushan Archipelago, eastern China. Video-derived shorelines along with their morphological parameters, such as dry beach width, dry beach area, beach orientation and unit width volume were analyzed during the monitoring period from June 2016 to July 2017. Analysis of video monitoring data shows that shorelines retreated during autumn and winter when storms were intensive, while advanced in spring and summer, with a lot of bulges occurred after nourishment projects. Abrupt variations in the beach orientation were always followed by gradual recoveries to the average beach orientation, while continuous counter-clockwise rotation occurred after March, 2017 when storm events were sparse. Comparing the different beach responses to individual storm events, we found that small-scale and short-interval sand nourishment implemented timely after storms can compensate for sediment loss more effectively on this beach. This study can provide a reference for local beach management.

Sand-mud transition dynamics at embayed beaches during a typhoon season in eastern China

“…1b) located in approximately 20 m depth. The dominant wave direction in the study area is from the east, and the waves with larger significant wave heights mainly come from the directions between northeast and southeast (Guo et al, 2020). The maximum significant wave height observed by the wave buoy during the 2019 typhoon season was 6.77 m.…”

“…There were four typhoons of different classifications in the study area during the 2019 typhoon season: Tropical Storm Danas, Super Typhoon Lekima, Super Typhoon Lingling, and Typhoon Tabah. The annual average significant wave height and the mean wave period in the study area are only 0.82 m and 3.6 s (Guo et al, 2020), while the average significant wave height was 1.16 m during the typhoon season of 2019, with a mean wave period of 5.5 s (Fig. 3a & 3b).…”

“…The construction of seawalls and frequent storms resulted in dominant beach erosion for years (Guo et al, 2018). In order to fight against stormdriven erosion and increase the dry beach area, beach nourishments have been performed with a total of 52,000 m 3 placed on Dongsha beach between 2016 and 2017, with large impact on beach processes (Guo et al, 2020).…”

Beach nourishment has complex implications for the future of sandy shores

“…The 'success' of beach nourishment projects, viewed in terms of how the sand is redistributed by waves and wind, can be difficult to assess accurately as there is no single set of widely agreed criteria and the success depends on the objective 28 . Consequently, using retention time of sand in the original placement region as the prime criterion to assess 'success', can lead to the conclusion that the nourishment has failed, especially if the objective was to locally increase beach width for recreation 49,65 or provide a temporary buffer to storm impacts on landward infrastructure 66 .…”

“…Local erosion trends and risks to infrastructure, projections of local sea-level rise, availability of sand, and societal values vary across the globe (Box 1), and future nourishment strategies must reflect these differences. For some locations small scale nourishments with lifespans of a month might be preferred (for example, as at Dongsha beach, China 66 ), whereas large scale nourishments are designed to last decades at other locations (as with the Sand Engine, Netherlands 52 ).…”