Evolution of the groundwater environment under a long-term exploitation in the coastal area near Zhanjiang, China

Aquifers consisting of unconsolidated sediments in the coastal area near Zhanjiang in southern China are grouped into the shallow, middle-deep and deep aquifer systems. Groundwater exploitation began in the 1950s in this district and has increased from year to year since 1980. Measurements of groundwater levels and monitoring data of groundwater chemistry at some 60 wells since 1981 are examined to analyze the evolution of hydrodynamics and hydrochemistry in the coastal aquifers. The results indicate that groundwater levels in the middle-deep and deep aquifer systems have fallen continuously and the extents of the depression cones in water levels have increased in the past two decades, even though the water levels recovered to some degree during the period of 1997–2001. In 2004, the lowest water levels in the middle-deep and deep aquifer systems were 23.58 and 21.84 m below sea level, respectively. The groundwater has TDS ranging from 40 to 550 mg/L, and is of low pH, commonly varies between 4 and 7. Concentrations of total iron and manganese exceed the concentration limits of the drinking water standards. The hardness is in the range of 10–250 mg/L. Chloride contents of the groundwater range from 10 to 60 mg/L. The chloride and TDS do not show systematically increasing trends. Although the water levels in the exploitation center near the coast are significantly lower than the sea level and the depression cones of water levels in the middle-deep and deep aquifer systems have expanded to the sea, sea water intrusion has not been observed until recently. This phenomenon is quite unique in the coastal area near Zhanjiang.     

Hydrodynamics and scale up in Rushton turbine flotation cells: Part 1 — Cell hydrodynamics

The effect of operating parameters on the hydrodynamics of three geometrically similar Rushton turbine flotation cells with volumes of 2.25, 10 and 50 dm³ was determined. The operating parameters investigated were superficial gas velocity (J_g), impeller rotational speed (N), and frother (methyl isobutyl carbinol, MIBC) concentration.     

Numerical modeling of the Amazon River plume

Marine circulation above the northern Brazilian continental shelf is subject to energetic forcing factors of various origins: high water buoyancy fluxes induced by the Amazon River freshwater discharge, a strong coastal current associated with a mesoscale current (North Brazil Current (NBC)), a forcing by semidiurnal tide and by Northeast or Southeast trade winds according to the season. Using a three-dimensional (3-D) hydrodynamic numerical model (MOBEEHDYCS), and realistic bathymetry and coastline of the northern Brazilian shelf, this paper aims at studying the influence of some specific physical processes on the morphology of the Amazon plume. The very large volume discharge (180 000 m³/s on average) and the weak effect of Coriolis force are additional characteristics of the studied system, which induce a particular dynamics. The various forcing factors are successively introduced into the model in order to simulate and to determine their respective influences upon the plume extent and the hydrodynamics at the shelf scale. Simulation reveal that the coastal current is at the origin of the permanent northwestward Amazon plume extension while wind effect can either reinforce or moderate this situation. The tide intervenes also to modify the position of the salinity front: a horizontal migration of salinity front is observed under its action.     

Spatial flow and sedimentation patterns within patches of epibenthic structures: Combining field,flume and modelling experiments

The objectives of the present study were twofold: (1) to identify spatial sedimentation and erosion patterns developing within patches of epibenthic structures (i.e. physical structures that protrude from the sediments, originating either from animals or plants) as a consequence of biophysical interactions; and (2) to assess the relevance of hydrodynamic flume studies for the long-term sediment dynamics in the field. We addressed these objectives by using patches of well-defined artificial structures (bamboo canes) for which we could easily monitor the long-term sediment dynamics in the field, measure the hydrodynamic effects in detail in the flume, and simulate the field and flume set-up with a commercially available hydrodynamic model. Two-year monitoring in the field showed that sedimentation was much larger in the high-density patches than the low-density ones. Within the high-density patches, comparable spatial patterns emerged at different field sites: erosion at the front and the side of the patches, and sedimentation more down-stream within the patches. The low-density patches showed no such patterns, and were generally characterised by some small-scale erosion directly around individual bamboo canes. Sedimentation and erosion in the field was well explained by the patterns in bed shear stress that were derived from our flume measurements. The 3D hydrodynamic modelling facilitated up-scaling of the flume results to the field, but failed to simulate accurately the effects at the leading edge. We conclude that: (A) field observations on sedimentation revealed interesting spatial patterns, but could not elucidate underlying processes; (B) detailed hydrodynamic measurements in a flume can elucidate these underlying processes, provided that appropriate scaling is being used; (C) flume studies are by definition not able to capture all spatial scales that are relevant for estuarine landscape formation and will always cause some flow artefacts; (D) hydrodynamic modelling offers a valuable tool to upscale flume observations, even though present models are not yet capable of fully reproducing all detailed spatial patterns; and (E) spatial heterogeneity is very important when looking at small-scale patches. There is a need for more spatially explicit and scale-dependent knowledge on bio-physical interactions.     

基于EFDC模型的深圳水库富营养化模拟

基于EFDC模型构建了深圳水库三维水动力和富营养化定量模拟模型.分别用2009年和2010 2011年流量、水位和水质等观测数据对模型进行了校正和验证,准确地反映了深圳水库的水动力和水质变化过程.在此基础上,假定支流污染截排、水库调度和降低东江引水污染负荷3种情景进行深圳水库富营养化数值模拟,3种情景下库中Chl.a峰值浓度分别降低1.0%、16.4%和46.3%,平均浓度分别降低1.3%、29.8%和29.9%.深圳水库具有良好的交换能力,尚未出现水华暴发,但入库营养盐负荷高,存在较大的富营养化风险;在目前沙湾河污水已经截排的基础上再实施支流污染控制,对水质改善和藻类控制作用已不明显;水库调度和削减东江引水污染负荷对深圳水库水质和富营养化改善明显,能够有效降低水华发生的风险.     

面向流量管理的水动力对淡水藻类影响的概念机制

许多证据表明缓慢的水动力条件是水华暴发的重要诱因,尽管以临界流速和水体置换为基础的流量管理实践在水华控制中已见成效,但受限于水动力对藻类生长小生境的干扰机制尚不明晰,长期的流量管理实践效果并不理想.在长期野外观测、围隔实验和室内模拟等一系列研究的基础上,以现有水动力对藻类影响机制的讨论为依据,从细胞学角度提出了水动力对藻类生长影响的3种不同的概念机制,即低强度的水力扰动导致藻细胞外扩散层厚度变薄,有利于周边水体向藻细胞输送营养物质,促进藻类生长;中等强度的水力扰动导致藻类营养盐吸收及光合作用能力受损,抑制藻类生长;高强度的水流剪切导致藻细胞壁破损.基于该机制认为流量管理中临界流速应分别从水体置换和细胞学两方面考虑.研究结果可为流量管理中控制藻类水华暴发和维持水体水质的策略提供重要的理论支持.     

河道型水库水动力特征与气候条件的响应关系

气候条件(降雨、气温)的变化对流域内水资源、河道、湖库的径流影响较大.河道型水库由于具有河道和湖泊的双重特点,受气候条件的影响则更为显著.本文以广东省梅州的河道型水库——长潭水库为例,耦合流域分布式水文模型SWAT与环境流体动力学模型EFDC,研究了河道型水库水动力特征(以水龄表征)与气候条件的响应关系.根据梅县气象站1953-2010年共58年的年均降雨量资料的频率分析,选取降雨量保证率分别为20%(丰水年)、50%(平水年)和90%(枯水年)年份的气候条件作为3种气候方案,对应的典型年分别为1992、1988和2004年,并将各典型年的日均降雨量和气温作为SWAT水文模型的输入条件,模拟了进入长潭水库各主要支流的日均变化过程.并将该流量过程作为长潭水库库区水动力模型的入流边界,模拟了各种降雨典型年情景下长潭水库的水动力变化过程.结果表明,长潭水库库区水龄沿程逐渐增大,呈指数增长的趋势,且受气候条件的影响很大.与丰水年相比,平水年、枯水年年降雨量分别减少了14%和49%,入库径流分别减少了23%和62%,水库出库坝址附近水龄分别增大了66%和247%,支流区域水龄增幅可达81%和290%左右,可见水库水动力特征受气候条件影响很大,而支流区域受气候条件影响更显著.不同气候条件下,河道型水库分别呈现出河道和深水湖泊的双重特性.丰水年时,坝址附近垂向上水体交换频繁,水龄均匀,呈现出河道的特性;平水年与枯水年时,坝址附近水体垂向交换较弱,逐渐呈现出深水湖泊的垂向分层特性.另外,流域分布式水文模型SWAT与环境流体动力学模型EFDC的联用,为弥补历史长系列高频监测资料的缺失,提高湖库水动力模型模拟的精度提供了有效的方法.     

厦门港南部附近海域的水动力输运特征

本文采用二维浅水潮流方程,欧拉余流模型和拉格朗日余流模型,并通过数值模拟的方法,研究了厦门港南部附近海域的水动力输运特征。结果表明,该海域的水动力输运条件良好,水交换能力罗强。     

Hydrodynamic response of a pneumatic floating platform

This paper describes a numerical approach to model the dynamic response of a pneumatic floating platform, and the laboratory experiments and parametric study to verify the numerical results. The pneumatic platform is composed of an array of open-bottom vertical cylinders trapping pressurized air that displaces the water. The cylinder diameter is assumed to be small compared to the wavelength and the water inside each cylinder oscillates as a piston. These assumptions simplify the mathematical formulation in that the bottom of the platform can be treated as a continuous surface on which the source distribution method can be applied. In the laboratory experiments, the compressibility and displacement of the trapped air are modeled by a spring and float assembly. The comparison between the numerical and experimental results indicates favorable agreement. The oscillation of the water columns and the overall dynamic characteristics of the platform are illustrated and discussed in the parametric study.     

Hydrodynamics of an oscillating articulated eel-like structure

This study examines the hydrodynamic performance of a highly simplified eel-like structure consisting of three articulated segments with the two aft segments oscillating. A physical model was built and tested to determine the forces developed with the model stationary, to find the self-propulsion speed, and to explore the effect on hydrodynamic performance of different swimming patterns. It was found that hydrodynamic performance increases with increasing oscillation frequency; the highest forces when stationary, and the highest self-propulsion speeds were produced by swimming patterns in which the amplitude in the aft segment is larger than that in the forward segment, and in which the motion of the aft segment lags the forward segment.A simple semi-empirical model based on Morison’s equation was implemented to predict the hydrodynamic forces. This was shown to predict mean thrust well in cases in which the aft segment oscillates in phase with the forward segment, but less reliably when the phase difference between the segments increases. Force time histories are generally not well-predicted using this approach. Nonetheless, self-propulsion speeds are predicted within 30% in all cases examined.