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On the role of a permeable groin in beach morphodynamics during sea-breeze events

Hofman, A. (2016) On the role of a permeable groin in beach morphodynamics during sea-breeze events.

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Abstract:While not directly in the line of most hurricanes that strike the peninsula or head to the United States, the north coast of the Yucatán peninsula is vulnerable to various physical and socioeconomic impacts due to strong winds and storms. Strong winds cause energetic waves to occur, despite the area being a low-energy wave area due to the wide and shallow continental shelf. Strong diurnal sea breezes drive sediment transport parallel to the coast, while ports and coastal structures induce large longshore transport gradients, hence beach erosion is obliquus in causing damage in coastal infrastructure along the coast. In order to solve local erosion problems, local measurements involving impermeable structures are often introduced as a coastal mitigation measure. However, these measurements often cause downdrift erosion problems due to the lessening of sediment budget transferred along the coast. In order to create a solution for the downdrift effect of impermeable structures, a permeable structure was tested in Sisal, Yucatán during one sea-breeze event. Field observations were conducted to characterize natural wave conditions, wind climate, tidal climate and beach morphology. Testing was done using a 24h experiment, in which continuous monitoring of beach morphology ensured correlation with natural forcing conditions. Afterwards, beach recovery was monitored to get an impression regarding beach resilience. Results were compared to observations from a similar field experiment conducted with an impermeable groin. During spring period, natural variability of the beach in Sisal was found to be tied to sea-breeze events. From interpretation of the longshore sediment transport formulas of Kamphuis and the USACE/CERC it was estimated that the rate of longshore sediment transport was influenced by local sea conditions. Volumetric change varied during the day, with beach profiles closely near the (semi)-permeable groin showing volumetric gain at the updrift side and erosion at the downdrift side. Shoreline change around the permeable groin resembled closely the typical pattern found at shoreline changes around an impermeable groin marked by volume gain on the updrift side and volume loss found on the downdrift side. The impact of the permeable groin on the beach over 24h is significantly less, expressed in the total volume gain of 18 m3 for the permeable groin and 60 m3 for the impermeable groin. Beach resilience was found to be very strong, with the beach being able to recover from the influence of the structure within 24 hours after removal of the permeable groin. Due to the big similarity between the shoreline changes around impermeable and permeable groins, it was concluded that the impermeable groin used during the experiment did not possess a significant advantage over the use of an impermeable groin. Also, it was concluded that despite permeable groin not having a quantitative advantage over the permeable groin, it had a qualitative advantage, it being able to reduce downdrift erosion problems due to its permeability on short term. However, long term advantages/disadvantages could not properly be assessed and therefore, it was recommended that long-time effects of a permeable groin have to be inspected and that the different degrees of permeability should be tested.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
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