• Journal of Ocean Engineering and Technology
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• v.31 no.2
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• pp.130-140
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• 2017

Typically, a submerged breakwater is one of the good scene-friendly coastal structures used to reduce wave energy and coastal erosion. However, sometimes, a submerged breakwater also has a negative aspect in that a strong rip current occurring around an open inlet due to a difference in mean water levels on the front and rear sides of the structure leads to scouring. Such scouring has a bad effect on its stability. In order to eliminate this kind of demerit, this study investigated four new types of submerged breakwaters with drainage channels. First, hydraulic experiments were performed the typical and new structures. Then, the wave height and mean water level distributions around the structures were examined using the experimental results. Finally, it was revealed that the new type of submerged breakwater could efficiently reduce the mean water level on its rear side. In particular, in the case of new-type submerged breakwater 2, an average reduction efficiency of 71.2% for the difference between the mean water levels at the front and rear sides was shown in comparison with the typical one.

• Journal of Korea Water Resources Association
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• v.57 no.3
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• pp.209-223
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• 2024

In the context of the fourth industrial revolution, data-driven decision-making has increasingly become pivotal. However, the integrity of data analysis is compromised if data quality is not adequately ensured, potentially leading to biased interpretations. This is particularly critical for water level data, essential for water resource management, which often encounters quality issues such as missing values, spikes, and noise. This study addresses the challenge of noise-induced data quality deterioration, which complicates trend analysis and may produce anomalous outliers. To mitigate this issue, we propose a noise removal strategy employing Wavelet Transform, a technique renowned for its efficacy in signal processing and noise elimination. The advantage of Wavelet Transform lies in its operational efficiency - it reduces both time and costs as it obviates the need for acquiring the true values of collected data. This study conducted a comparative performance evaluation between our Wavelet Transform-based approach and the Denoising Autoencoder, a prominent machine learning method for noise reduction.. The findings demonstrate that the Coiflets wavelet function outperforms the Denoising Autoencoder across various metrics, including Mean Absolute Error (MAE), Mean Absolute Percentage Error (MAPE), and Mean Squared Error (MSE). The superiority of the Coiflets function suggests that selecting an appropriate wavelet function tailored to the specific application environment can effectively address data quality issues caused by noise. This study underscores the potential of Wavelet Transform as a robust tool for enhancing the quality of water level data, thereby contributing to the reliability of water resource management decisions.

• Journal of Wetlands Research
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• v.16 no.3
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• pp.431-440
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• 2014

To propose the improvement and management plans to strengthen the pollutant removal efficiency of dam reservoir's constructed wetlands(CWs), the operation status and configuration of CWs (including water depth, operational flow, water flow distribution, residence time, and pollutant removal efficiency, aspect ratio, open water/vegetation ratio etc.) were analyzed in 10 major wetlands constructed in dam reservoirs. The pollutant concentrations in the inflows of the studied CWs were lower than those of American and European constructed wetlands. Especially, organic matter concentrations in all of inflows were below 3 mg/L(as BOD) due to advanced treatment of sewage disposal plant and an intake of low concentration water during dry and normal seasons. The average removal efficiency of total nitrogen(TN) and total phosphorus(TP) for 10 CWs ranged from 7.6~67.6%(mean 24.9%) and -4.9~74.5%(mean 23.7%), respectively, showing high in wetlands treating municipal wastewater. On the other hand, the removal efficiency of BOD was generally low or negative with ranging from -133.3 to 41.7%. From the analysis of the operation status and configuration of CWs, it is suggested that the low removal efficiency of dam reservoir's CWs were caused by both structural (inappropriate aspect ratio, excessive open water area) and operational (neglecting water-level management, lack of facilities and operation for first flush treatment, lake of monitoring during rainy events) problems. Therefore, to enable to play a role as a reduction facility of non-point source(NPS) pollutants, an appropriate design and operation manuals for dam reservoir's CW is urgently needed. In addition, the monitoring during rainy events, when NPS runoff occur, must be included in operation manual of CW, and then the data obtained from the monitoring is considered in estimation of the pollutant removal efficiency by dam reservoir's CW.