Enhanced hysteresis of suspended sediment transport in response to upstream damming: An example of the middle Yangtze River downstream of the Three Gorges Dam

The peak in sediment transport in alluvial rivers generally lags behind the peak in discharge. It is thus not clear how the hysteresis in the sediment/discharge relationship may be impacted by damming, which can fundamentally alter the water and sediment regimes in the downstream reaches of the river. In this study, a total of 500 flood events in the Yichang–Chenglingji Reach (YCR) of the Middle Yangtze River immediately downstream of the Three Gorges Dam (TGD) are analysed to study the impacts of dam operations on the hysteresis of suspended sediment transport. Sediment rating curves, hysteresis patterns, as well as lag times, are investigated to determine the relationship between suspended sediment concentration (SSC) and flow discharge (Q) at different temporal scales, from inter-annual to individual flood events, for the pre- and post-TGD period from 1992 to 2002 and from 2003 to 2017, respectively. The results showed that the TGD operation decreased the frequency and magnitude of floods. The decrease in peak flow and increase in base flow weakened the flood contribution to the annual discharge by nearly 20%. However, the relative suspended sediment load contribution during flood events was much higher than the discharge contribution, and was little impacted by the dam. At seasonal and monthly scales, more than 80% of the suspended sediment was transported by ~65% of the water discharge in the summer and early autumn. The monthly SSC–Q relationship changed from a figure-eight to an anti-clockwise pattern after the construction of the TGD. For single flood events, the TGD operations significantly modified the downstream SSC–Q hysteresis patterns, increasing the frequency of anti-clockwise loops and the lag time between peak Q and peak SSC. These adjustments were mainly caused by differences in the propagation velocities of flood and sediment waves and the sediment ‘storage–mobilization–depletion’ process, whereas the influence of lateral diversions was small. © 2020 John Wiley & Sons, Ltd.     

Dynamic Compaction of Ultra-High Energy in Combination with Ground Replacement in Coastal Reclamation Areas

This paper presents a case study of dynamic compaction (DC) on backfill ground for planned oil tanks located at Nanjing Bay. The ultra-high energy DC level of 18,000 kN · m was applied in the area tamping phase of the dynamic compaction. In combination with ground replacement technique by forcing crushed stones into the underlain cohesive layer, the high-compressibility of this layer was properly tackled. The construction techniques and ground improvement mechanisms are introduced and discussed. Field evaluations before and after the dynamic compaction, including surface wave test, plate load test, and soil sampling, showed that the ultra-high energy dynamic compaction in combination with ground replacement achieved much greater improvement depth and ground bearing capacity than conventional DC. Results show that dynamic compaction of 18,000 kN · m combined with ground replacement is of great merit in dealing with backfill ground with weak cohesive content in harbor development.     

高建筑物对矮建筑物保护作用的三维数值模拟

运用三维高分辨率随机多先导连接模型, 设置高矮两座建筑物并改变其中矮建筑物的高度以及高矮两座建筑物水平距离, 同时设置孤立矮建筑物进行对照, 探究多先导模式下高建筑物对矮建筑物的保护作用。结果表明:高矮建筑物距离较近时, 下行先导的发展完全受高建筑影响;随着建筑物水平距离增加, 高建筑物对先导主通道仍然存在明显吸引效应。当矮建筑物雷击概率的增长趋势出现明显减缓的分界点, 此时与孤立矮建筑物的雷击概率仅相差3.6%, 但单次闪电的连接过程仍存在显著差异。通过对比不同建筑物水平距离与孤立建筑物的雷击结果, 高矮建筑物水平距离由400 m增至600 m, 差异则从44.5%降低至22.7%。在相同高建筑物影响下, 不同高度矮建筑物的雷击概率变化趋势亦存在该特征, 高度为50, 100, 150 m和200 m的矮建筑物对应的雷击增长速率分界点的水平距离为300, 450, 550 m和600 m。     

Copula函数在广西洪涝灾害的降水概率预测中的应用

为了研究洪涝的重要致灾源因子降水的概率,利用广西从1970年-2012年的降水数据,以年降水均值（X）和年降水极值均值（Y）为研究变量,通过Copula函数构建其联合分布.经过OLS,AIC拟合优度评价,采用Copula函数中拟合效果较好的Gumbel-Hougaard Copula函数建立边缘分布为Pearson-Ⅲ型的两变量的联合分布.随后,进行相应的重现期计算,计算结果表明,在联合重现期下的两变量降水设计值比单变量设计值和同现重现期下的设计值都要高,故采用联合重现期下的联合设计值作为防洪标准会更加安全.最后,对比降水数据与灾情数据,研究降水重现期与洪涝灾情的关系.结果表明,降水的重现期越长,洪涝灾害也越严重.     

洪湖日本沼虾的种群繁殖生物学

１９９４年５月至１９９５年６月对洪湖日本沼虾的种群繁殖生物学进行了研究。洪湖日本沼虾的繁殖期为４月中旬至１０月上旬,５月中旬至８月中旬为日本沼虾的繁殖高峰期,其中６月、８月雌虾抱卵率均在７０％以上;日本 虾群体中雄性总是少于雌性,月性比（♀／♂）变化于１．１０４－５．７８０之间,３－６月性比逐渐增高,７－１０月性比则逐渐降低;在整个繁殖期,４－７月的抱卵是均为前一年出生的大、中规格的个体,之后当年     

Biogenic and abiogenic polynuclear aromatic hydrocarbons in sediments from two remote Adirondack lakes

Sediment cores from Sagamore Lake and Woods Lake in New York State's Adirondack Park, an area remote from industrial activities, were analyzed for polynuclear aromatic hydrocarbons (PAH) by high resolution gas chromatography/mass spectrometry (GC/MS). Their composition and distribution with depth in the sediment indicate that the parental PAH in the surface sediments are primarily produced by anthropogenic combustion of fossil fuels. Perylene in deep sediments is apparently transformed from natural precursors in the reducing environment, however, the exact precursors remain unknown. The rather even sediment distributions of the non-parental PAH differ from the parental, suggesting biogenic origins. Based on their chemical structures, retene and alkylated and partially hydrogenated phenanthrenes are believed to be biogenically converted from abietic acid; hydrochrysenes and hydropicenes, from pentacyclic triterpenes.     

滇东北彝良-两河地区控煤构造研究中遥感技术的应用

以卫星遥感图像为数据源,采用遥感图像解译和野外调查验证、以及常规地质资料分析相结合的综合调查方法,对自然地理条件差、交通不便的彝良-两河地区的控煤构造特征进行了研究。结果表明:该区以褶皱断裂组合为主,煤系在向斜核部和较缓的一翼由于受构造破坏较小,保存完整。运用构造控煤理论,圈定了含煤远景区,为区内煤炭资源调查评价起到了较好的指导作用。     

城市地下空间适宜性评价研究国内外现状及趋势

城市地下空间的开发利用是城市可持续发展的必然途径.科学合理的城市地下空间适宜性评价可为城市的立体规划提供决策依据.因此,对城市各区域开展地下空间的适宜性评价就显得尤为重要.从城市地质模型的可视化、地下空间适宜性评价指标、权重体系、评价模型、评价模式及评价系统这6个方面,系统梳理了城市地下空间适宜性评价的国内外研究现状;...     

A rapid assessment method for calculating the drag coefficient in wave attenuation by vegetation

Vegetation in wetlands is a large-scale nature-based resource that can provide multiple benefits to human beings and the environment,such as wave attenuation in coastal zones.Traditionally,there are two main calibration approaches to calculate the attenuation of wave driven by vegetation.The first method is a straightforward one based on the exponential attenuation of wave height in the direction of wave transmission,which,however,overlooks the crucial drag coefficient (C_D).The other method is in accordance with more complicate equations for predicting the damping factor,which is regarded as a function of C_D.In this study,a new relation,combining these above two conventional approaches,is proposed to predict the C_D in an operative approach.Results show that values yielded by the new assessment method perform a strong linear relationship with a collection of historical observations,with a promising R~2 value of 0.90.Besides,the linear regression derives a new predictive equation for the bulk drag coefficient.Additionally,a calibrated value of 4 for the empirical plant drag coefficient(C_P) is revealed.Overall,this new equation,with the superiority of the convenient exponential regression,is expected to be a rapid assessment method for calculating wave attenuation by vegetation and predicting the drag coefficient.     

基于粗集理论的声呐图像中值滤波

保边去噪是图像滤波中的主要问题。声呐图像像素少品质恶劣,保边去噪显得尤为重要。将基于粗集理论的中值滤波应用于声呐图像处理中,给出了实验结果。结果表明这种方法具有可行性。