Non-symmetrical levee breaching processes in a channel bend due to overtopping

A series of experiments were done to reveal the overtopping breaching process of non-cohesive and cohesive levees in a U-bend flume. The flood hydrograph and breaching geometry were measured and analyzed in detail. The results show that the levee breaching processes can be briefly divided into four stages: slope erosion, longitudinal headward gully-cutting, lateral erosion, and relative stabilization. For non-cohesive levees, non-symmetrical lateral development of the breach occurs throughout the four stages, and the final non-symmetrical coefficient is approximately 2.2–2.6. Larger flow discharge or higher water level can accelerate the breaching process, while coarser sands tend to accelerate the process initially but depress the process at the end. The fluvial erosion rate of a non-cohesive breach shows a power-function relation with the excess wall shear stress. For cohesive levees, a plateau forms in the breach partially blocking the flow in the first two stages. The breach flow is approximately perpendicular to the levee body, and, thus, the erosion rates of the two breach sides are almost the same. Non-symmetrical lateral development mainly occurs in the third stage when the deep gully forms. The final non-symmetrical coefficient is approximately 2.7–3.3. It is expected that these findings can provide a valuable experimental dataset and a theoretical basis for breach closure and flood alleviation.     

莱州湾海岸带环境与功能区划初探

利用国家海洋局第一海洋研究所2007—2008年莱州湾地下水监测数据,在甄别、整理的基础上,进行了相关分析、主成分和聚类分析。根据聚类分析各类别的地下水质特征,同时考虑到区域的可持续发展,划分出海水入侵预防治理区、海水入侵重点治理区、养殖与海化产业区和海化工业区共四个区域。     

Hydrological cycle and water balance estimates for the megadune–lake region of the Badain Jaran Desert,China

The hydrology and water balance of megadunes and lakes have been investigated in the Badain Jaran Desert of China. Field observations and analyses of sand layer water content, field capacity, secondary salt content, and grain size reveal 3 types of important natural phenomenon: (a) vegetation bands on the leeward slope of the megadunes reflect the hydrological regime within the sandy vadose zone; (b) seepage, wet sand deposits, and secondary salt deposits indicate the pattern of water movement within the sandy vadose zone; (c) zones of groundwater seeps and descending springs around the lakes reflect the influence of the local topography on the hydrological regime of the megadunes. The seepage exposed on the sloping surface of the megadunes and gravity water contained within the sand layer confirm the occurrence of preferential flow within the vadose zone of the megadunes. Alternating layers of coarse and fine sand create the conditions for the formation of preferential flows. The preferential flows promote movement of water within the sand layer water that leads to deep penetration of water within the megadunes and ultimately to the recharging of groundwater and lake water. Our results indicate that a positive water balance promotes recharge of the megadunes, which depends on the high permeability of the megadune material, the shallow depth of the surface sand layer affected by evaporation, the occurrence of rainfall events exceeding 15 mm, and the sparse vegetation cover. Water balance estimates indicate that the annual water storage of the megadunes is about 7.5 mm, accounting for only 8% of annual precipitation; however, the shallow groundwater per unit area under the megadunes receives only 3.6% of annual precipitation, but it is still able to maintain a dynamic balance of the lake water. From a water budget perspective, the annual water storage in the megadunes is sufficient to serve as a recharge source for lake water, thereby enabling the long‐term persistence of the lakes. Overall, our findings demonstrate that precipitation is a significant component of the hydrological cycle in arid deserts.     

围岩参数Monte－Carlo有限元反分析

提出了应用隧道施工监测的随机值，采用蒙特一卡罗（Ｍｏｎｔｅ－Ｃａｒｌｏ）有限元随机反分析以反推地层参数和初始地应力分布的方法。反推参数不仅给出其均值，还给出参数的方差及分布类型，为地下结构稳定性和可靠性分析提供必要数据。为检验所提的反分析方法对工程的实用性，文中给出了一个实例。     

Paramonohystera weihaiensis sp.nov.(Xyalidae,Nematoda) from the intertidal beach of the Yellow Sea,China

A new species of free-living marine nematode of the genus Paramonohystera was described from the intertidal beach,Weihai.Paramonohystera weihaiensis sp.nov.is characterized by cervical region with a circle of long setae;tail sexual dimorphism,male tail angled dorsally with sharp narrowed of the body at the cloaca,female tail ordinary conico-cylindrical; spicules slender,2.5 abd long; gubemaculum plate,enlarged distal end with two teeth,without apophysis; precloacal supplements absent;Four caudal gland cells obviously extended to tail.The new species differs from the other fourteen known valid congeners by the combination of its characteristics:a circle of long cervical setae,tail sexual dimorphism,spicules slender,2.5 abd long,gubernaculum plate with a distal pair of teeth.     

HY-1C/D卫星中国海洋水色水温扫描仪几何定位方法

海洋一号C/D（HY-1C/D）卫星中国海洋水色水温扫描仪（Chinese Ocean Color and Temperature Scanner,COCTS）主要用于探测海洋水色、水温等要素,这些要素需要经过卫星资料处理才能获取,而几何定位是预处理的核心,直接影响这些要素的质量。COCTS具有114°视场角和四元逐点摆扫的特征,据此研究出一套完整的几何定位方法。从0级数据中提取卫星星历,利用插值法从中获取采样时间对应的卫星位置和速度,进而得到轨道（ORB）坐标系到地心旋转（ECR）坐标系的转换矩阵。基于四元逐点摆扫的特征,中心视矢量分别绕X轴、Y轴旋转相应角度,获得扫描行各采样点ORB视矢量,建立视矢量与地球交叉点关系模型,从而对根据波段数据绘制的遥感图像进行地理定位。本文使用插值法替代了传统需要6个轨道根数来计算卫星位置的复杂方法,同时直接计算ORB到ECR的转换矩阵,而不采用传统的两步转换方法。经过多组数据计算及定性定量验证,HY-1C/D COCTS几何定位结果一致;采样像元尺度效应导致从星下点到两侧边缘、从赤道到两极,误差逐渐增大,约在两个像元内。该方法满足一定的定位精度要求,可以用于COCTS的几何定位。     

Huanghe (Yellow River) and its estuary: Sediment origin, transport and deposition

The upper part of the Huanghe (Yellow River) drainage basin supplies 50–60% of the annual water discharge and only 10% of the total river sediment load, while the middle reaches contribute 30–40% of the water flow and 90% of the annual sediment load, because of severe erosion over the Loess Plateau. Large variations in both annual water discharge and sediment load occur in the Huanghe. Heavy sedimentation in the lower reaches of the channel makes the river bed aggrade several centimetres per year. Of the suspended sediment in the river, 90–95% is deposited in the lower part of the river course and in the coastal shallow water area; less than 5–10% escapes from Laizhou Bay and enters the Central Bohai and/or North Huanghai (Yellow Sea). The active delta complex now propagates seawards at a mean rate of 42 km² year⁻¹.     

面向目标自适应有限元法的带地形三维大地电磁各向异性正演模拟

传统三维大地电磁各向异性模拟均是基于规则六面体网格,计算精度有限且较难拟合复杂地质条件.本文采用面向目标自适应非结构矢量有限元法,对三维大地电磁各向异性介质进行模拟.首先从电场双旋度方程出发,利用伽辽金方法建立变分方程;然后利用电流密度连续性条件构建适合大地电磁各向异性问题的加权后验误差估计方法,实现面向目标的网格自适应正演;最后通过典型算例分析各向异性对网格自适应和大地电磁响应的影响特征以及各向异性的识别方法.本文算法能够高精度地拟合起伏地表和任意各向异性介质,适用于分析复杂地电条件大地电磁响应特征,为提高大地电磁资料解释水平提供了理论基础.

     

1960—2017年沈阳地区春播期降水变化特征

基于1960—2017年沈阳市5个气象观测站4—5月降水量资料,采用线性趋势法和累积距平分析了沈阳市春播期(4—5月)降水量演变特征,并分析首场透雨及最大连续无有效降水日数演变特征及对春播期降水量影响,对春播期降水量资源变化特征进行相关分析。结果表明:近58a沈阳春播期降水量整体呈现弱的增加趋势,平均每10a增加3.1mm,2004年开始降水量迅速增加,且波动性较大,降水量异常偏多或偏少年份较多,易诱发春旱春涝事件。春播期首场透雨出现日期平均每10a偏晚0.051d,首场透雨日期偏晚,将导致春播期前期雨水条件不足,引起土壤干旱,不利于春播开展。最大连续无有效降水日数呈波动性增加趋势,平均每10a增加0.56d,对4月降水量影响较大,虽然春播期降水资源总量增加,但存在降水资源时间分配不均的问题,且长时间无有效降水事件频发,将导致春播期干旱灾害事件发生风险加大,导致适播期延后。     

北美地区一次冬季中尺度对流系统上空红色精灵现象的空间观测及其母体雷暴分析

红色精灵是发生在雷暴云上空的一种大尺度瞬态放电发光现象,它们通常出现在地面上空40～90 km之间,是由地闪回击和随后可能存在的连续电流产生的。目前,由于综合同步观测资料较少,与夏季红色精灵相比,全世界对冬季红色精灵的研究屈指可数。2008年12月27～28日,受高空槽及低层暖湿气流的影响,北美阿肯色州地区爆发了一次冬季雷暴天气过程,搭载于FORMOSAT-2卫星上的ISUAL（Imager of Sprites and Upper Atmospheric Lightning）探测器有幸在这次雷暴上空记录到了两例红色精灵事件。本文利用ISUAL获取的红色精灵观测资料、多普勒天气雷达资料、美国国家闪电定位资料、超低频磁场数据、美国国家环境中心/气候预测中心提供的云顶亮温和探空数据等综合观测数据,对产生红色精灵的这次冬季雷暴特征和相关闪电活动规律进行了详细研究。结果表明,在两例红色精灵中,ISUAL均未观测到伴随的“光晕（halo）”现象,第一例为“圆柱状”红色精灵,第二例红色精灵由于发光较暗,无法判断其具体形态。产生红色精灵的母体雷暴是一次中尺度对流系统,该系统于27日15:00（协调世界时,下同）左右出现在阿肯色州北部附近,并自西向东移动。23:59系统发展到最强,最大雷达反射率因子（55～60 dBZ）的面积达到339 km2,之后开始减弱。03:03雷暴强度有所增加,随后云体便逐渐扩散,雷暴开始减弱,并在11:00完全消散。两例红色精灵发生分别在04:46:05和04:47:14,此时雷暴处于消散阶段,正负地闪频数均处于一个较低水平且正地闪比例显著增加,并且多位于云顶亮温?40°C～?50°C的层状云区上空。红色精灵的出现伴随着30～35 dBZ回波面积的增加。在红色精灵发生期间,雷达反射率大于40 dBZ的面积减少,10～40 dBZ的面积增加,表明红色精灵的产生与雷暴对流的减弱和层状云区的发展有关,这与已有的夏季红色精灵的研究结果类似。红色精灵的母体闪电为正地闪单回击,位于中尺度对流系统雷达反射率为25～35 dBZ的层状云降水区,对应的雷达回波顶高分别为2.5 km和5 km,峰值电流分别为+183 kA和+45 kA。根据超低频磁场数据估算两个母体闪电的脉冲电荷矩变化（iCMC）分别为+394 C km和+117 C km。超低频磁天线记录到了第一例红色精灵内部的电流信号,表明这例红色精灵放电很强。