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An artificial oyster shell reef was deployed in Rongcheng Bay, East China. However, the effects of this reef on the surrounding macrobenthic communities were unknown. We compared sedimentary factors, macrobenthic biomass, abundance, and community composition and ecological indicators between the reef and non-reef areas over a one year period. The mean values for chlorophyll a （Chl a）, total organic matter （TOM）, total organic carbon （TOC）, and total nitrogen （TN） content in surface sediments in the reef area were slightly higher than those in the non-reef area. The Chl a levels differed significantly between the two areas, but the TOM, TOC, and TN were not significantly different. The abundance of crustaceans was significantly different between the two areas, but the abundance and biomass ofpolychaetes, echinoderms, mollusk did not differ significantly. The permutational multivariate analysis of variance （PERMANOVA） revealed that the macrobenthic community differed significantly through time and analysis of similarity multivariate analyses （ANOSIM） revealed that the macrobenthic community differed significantly in some months. The ecological indicators revealed that the environmental quality of the reef area was slightly better than that of the non-reef area. Overall, our results suggest that the artificial oyster shell reef may change the macrobenthic community and the quality of the environment. Despite the lack of an effect in the short term, long-term monitoring is still needed to evaluate the effects of artificial oyster shell reefs on macrobenthic communities. 相似文献
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For the Xiamen coast where typhoon frequently occurs, beaches are subject to severe erosion during typhoons. To investigate storm-induced beach profile changes at Xiamen coast, four inner XBeach models were applied using typhoon Dan as a case study. These numerical simulations utilized hydrodynamic and wave conditions determined from larger-scale outer and middle coupled Delft3D-FLOW and SWAN models. The models were validated against historic measurements of tidal level, storm tide, storm surge and beach profiles, thus showing the accuracy of outer and middle models to provide boundary conditions and the reliability of inner models to reflect beach profile changes during a typhoon process. The applicability of this modeling approach to Xiamen coast was verified. The results also demonstrated that an enormous amount of dune face erosion occurred at the selected beaches during the typhoon Dan process and the slopes in the vicinity of zero elevation for the chosen four beach profiles all turned out to be gentler after typhoon Dan. Nevertheless, these beaches suffered different impact degrees and processes during the typhoon influence period. Compared to swash and collision regimes, overwash and inundation regimes have the ability to alter beach profile rapidly in short time. Post-storm beach profile with and without vegetation indicated that vegetation is capable of protecting coastal beaches to some extent. By running the nested models, the simulated results can be employed in the management of the beach system and the design of beach nourishment projects at Xiamen coast.
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In this study, a 91-year data set at the Wusong Station near Shanghai City in Yangtze Estuary has been used to estimate the 100-year Annual Maximum Water Level (AMWL). The performances of four common distribution models have been evaluated. The GEV model provides the best estimates of an AMWL. It results in the minimum difference (0.04 m) compared to the observed 92-year AMWL, with the high correlation coefficient (0.99) and minimum root-mean-square-error (0.045 m) value. Predictions from other distribution models cause non-negligible deviations, underestimating the 92-year AMWL by 0.57, 0.38, and 0.15 m for Weibell, Lognormal, and Gumbel distribution models, respectively. In order to examine the effects of a shorter data set, a 59-year data set was investigated. Model predictions using 59-year data set underestimates the observed 60-year AMWLs. By comparing to the 100-year AMWL estimated by the GEV distribution, using the 91-year data set, results using the shorter 59-year data set lead to underestimates of the 100-year AMWL by 0.78 m for Weibull, 0.58 m for Lognormal, 0.38 m for Gumbel, and 0.39 m for GEV distributions. Therefore, one should be cautious when estimating the 100-year AMWL if the data set covers a period much shorter than 100 years. Selecting an appropriate distribution model can improve prediction accuracy. 相似文献
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The prediction of high extremes in sustained water level is very important for coastal engineering design and planning. The recorded historical water level datasets in Colombo, Sri Lanka, are not long enough for the traditional frequency analysis in predicting extreme water levels, such as 50-, 100- and 200-year extreme water levels. In this study, the integrated ADCIRC + SWAN hydrodynamic model and Monte Carlo model have been applied to predict extreme water level in Colombo station of Sri Lanka. The meteorological driving forces of cyclone storm surge are simulated by Monte Carlo stochastic model. The calibrated ADCIRC model with SWAN wave model is used to simulate the potential surge setups with the driving forces generated by Monte Carlo model. By ranking the maximum high water levels in each storm surge procedure, the estimation on extreme high water levels for the desired return period is proposed in this study. The estimated extreme high water levels with return period of 50, 100 and 200 years are 1.28, 1.40 and 1.50 m correspondingly. The estimated extreme high water levels are recommended for engineering design and planning. 相似文献
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In the Coastal Flood Insurance Study by the Federal Emergency Management Agency (FEMA, 2005), 1% annual maximum coastal water levels are used in coastal flood hazard mitigation and engineering design in coastal areas of USA. In this study, a frequency analysis method has been developed to provide more accurate predictions of 1% annual maximum water levels for the Florida coast waters. Using 82 and 94 years of annual maximum water level data at Pensacola and Fernandina, performances of traditional frequency analysis methods, including advanced method of Generalized Extreme Value distribution method, have been evaluated. Comparison with observations of annual maximum water levels with 83 and 95 years of return periods indicate that traditional methods are unable to provide satisfactory predictions of 1% annual maximum water levels to account for hurricane‐induced extreme water levels. Based on the characteristics of annual maximum water level distribution of Pensacola and Fernandina stations, a new probability distribution method has been developed in this study. Comparison with observations indicates that the method presented in this study significantly improves the accuracy of predictions of 1% annual maximum water levels. For Fernandina station, predictions of extreme water level match well with the general trend of observations. With a correlation coefficient of 0·98, the error for the maximum observed extreme water level of 3·11 m (National Geodetic Vertical Datum) with 95 years of return period is 0·92%. For Pensacola station, the prediction error for the maximum observed extreme water level with a return period of 83 years is 5·5%, with a correlation value of 0·98. The frequency analysis has also been reasonably compared to the more costly Monte Carlo simulation method. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Natural Hazards - The central part of Khyber Pakhtunkhwa, Pakistan, is a highly flood-prone area of the province. The lives and assets of local communities are deeply vulnerable, attributed to the... 相似文献
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Natural Hazards - Continuing to enhance the understanding of occurrence probabilities of spatial extreme sea levels is a fundamental requirement of coastal hazard mitigation and prevention. To... 相似文献
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浅水三角洲作为沉积学和油气勘探领域的热点,目前研究主要集中在大型拗陷型盆地内,对断陷湖盆关注较少。通过充分调研区域地质背景并结合永安地区戴一段的岩心、录井、测井、地震、分析化验等资料进行系统研究后认为,戴一段处于断陷早期,地形较为平缓,水体宽浅且波动频繁,气候温暖湿润,物源供给充足,具备形成浅水三角洲的有利沉积条件。研究区浅水三角洲为近源沉积,以牵引流为主;砂岩中多见强水动力沉积构造;垂向上发育进积、加积的沉积序列,具平行、亚平行及叠瓦状地震反射特征;以前缘亚相为主体,相带宽阔,可分为内、外前缘沉积,水下分流河道构成主要骨架砂体;在向湖推进过程中受沉积物可容纳空间与沉积物补给量比值(A/S)变化的影响较大,不同成因砂体类型及沉积样式呈现有规律的分布。基于以上分析,最终建立了断陷湖盆早期浅水三角洲的沉积模式,在一定程度上对丰富浅水三角洲的沉积学认识并拓展永安地区乃至整个高邮凹陷斜坡带油气勘探的领域和范围具有一定指导意义。 相似文献