大型浅水湖泊沉积成岩模型不确定性与敏感性分析——以氮为例

随着太湖流域控源截污和面源整治的推行,底泥释放成为太湖不可忽视的污染源.本文基于EFDC模型构建太湖沉积成岩模型以动态模拟底泥释放过程,以氨氮和硝态氮为水质目标,采用拉丁超立方抽样抽取沉积成岩模型的18个参数进行不确定性分析,采用标准秩逐步回归法进行敏感性分析.结果表明：对于大型浅水湖泊,沉积物-水界面的硝化作用、反硝化作用和扩散过程对底泥氮的释放影响很大,太湖氮浓度的不确定性有明显的时空差异,并且受藻类生长影响;随藻类生长生化反应参数的敏感性逐渐减弱,动力参数的敏感性逐渐增强,氨氮的主要敏感参数为孔隙水扩散系数和最优硝化反应速率,贡献率分别是41.68%和37.82%,硝态氮的主要敏感参数为孔隙水扩散系数和表层反硝化作用反应速率,贡献率分别是29.15%和42.34%,这些参数的取值需予以着重考虑.本研究识别出太湖底泥氮释放的关键物化过程,为模型调参提供优先级并给出优化区间,对减小模型的不确定性、提高模型精度有参考意义,为定性指导大型浅水湖泊底泥释放的室内实验模拟提供依据.     

双向环形水槽模拟变化水位和流速下洞庭湖沉积物氮释放特征

浅水湖泊生态系统中的沉积物—水界面是湖泊内源氮释放的重要界面,而水动力因素是改变沉积物氮释放的重要因素.三峡大坝修建以后,长江中下游通江湖泊的水动力条件发生了明显的变化.通过采集洞庭湖湖口区域的沉积物和水样,在双向环形水槽动力模拟装置内模拟湖泊水位和流速的变化,探讨湖泊沉积物氮在沉积物和水系统中的二次释放特征.结果表明,随着扰动强度的增加,上覆水悬浮物浓度增大,上覆水中总氮浓度增加,沉积物向上覆水释放氮的强度增强,水动力条件的改变所引起的沉积物内源氮释放不容忽视.在该模拟实验条件下,沉积物存在最适扰动水位(20cm),此水位下上覆水中悬浮物浓度最低,总氮浓度最小.水动力条件的改变对上覆水和沉积物—水界面处铵态氮和硝态氮浓度的影响并不明显,孔隙水中铵态氮与硝态氮之间发生形态的转化.     

大型浅水湖泊藻类模型参数敏感性分析

选取太湖作为典型湖泊在之前研究基础上建立藻类模型,对模型中与藻类有关的40个参数进行拉丁超立方抽样,并使用区域敏感性分析方法和普适似然不确定性分析方法进行敏感性分析.结果表明:在所选的40个参数中,有7个参数是敏感的参数,对模拟的结果影响较大.在藻类生长、基础代谢、牧食和沉降4个藻类变化过程中藻类生长的敏感参数最多,影响最大;在藻类生长项中,叶绿素的消光系数是藻类生长光照限制中的最敏感参数,而最低适宜生长温度及其对藻类生长的影响系数则是温度限制中的敏感参数;并且不同湖区的不确定性在不同时间差异明显,对于藻类低浓度湖区和藻类暴发期的模拟需要加以关注.     

鄱阳湖二维水动力和水质耦合数值模拟

针对大型通江湖泊水位变化剧烈,地形起伏多变,岸线复杂,湖泊内部窄小洪道与大面洲滩和洼地连接复杂,湖泊洲滩出露、淹没频繁交替等湖泊水情和地貌特征,基于二维浅水方程和对流扩散方程组构建了鄱阳湖二维水动力和水质耦合模拟模型.模型采用非结构网格有限体积法进行离散,以HLLC算法计算单元界面的水量、动量和物质输运通量.水陆边界通...     

Comparing single-phase,non-Newtonian approaches with experimental results: Validating flume-scale mud and debris flow in HEC-RAS

Post-fire debris flows and tailing impoundment failures destroy lives and property. These geologic hazards – and other similar processes – fall on a continuum between classic Newtonian flood analyses and geotechnical stability analyses. The US Army Corps of Engineers (USACE) is developing a non-Newtonian library (DebrisLib) that includes a suite of rheological and clastic approaches to hyper-concentrated, mudflow and debris flow dynamics. The Hydrologic Engineering Center (HEC) has implemented these non-Newtonian methods into the widely used, public-domain open-channel hydraulics and morphodynamic software, HEC-RAS (river analysis system). This work presents part of the verification and validation of these non-Newtonian approaches, applying several rheological equations to published laboratory results high-concentration flume experiments. This study tested the linear Bingham model as well as the turbulent and Bagnold quadratic terms of the O'Brien equation. HEC-RAS also includes the non-linear Herschel–Bulkley (HB) approach, which quantifies shear-thickening or shear-thinning processes. The study used these non-Newtonian models in HEC-RAS to simulate 10 of Parsons et al.’s (2001) flume experiments, which measured the snout and plug velocity of fluids with high solid concentrations (C_v = 68–74%) and a broad range of material gradations (d₅₀ = 0.05–1 mm, d₁₅ = 0.006–0.1 mm). The experiments also measured and back-calculated Bingham and HB parameters of the materials, finding HB powers between 0.45 and 1.25 (i.e. fluids that are dilatant, pseudo-plastic and visco-plastic). The rheological models incorporated into DebrisLib and implemented in HEC-RAS reproduce experimental data well for most experiments. The Bingham model generated a plug velocity root-mean-square error (RMSE) of 0.21 m/s using standard flow parameters and Parsons et al.’s calibrated parameters, a substantial improvement over the unmodified shallow water flow equations (RMSE 0.77 m/s). Experiments with strong snout effects tended to generate higher residuals, especially in the snout velocity. The RMSE associated with the O'Brien equation was larger with the Parsons et al. fit parameters, but similar (0.23 m/s) with measured parameters. The turbulent parameter was the largest (often the dominant) parameter in most O'Brien simulations, with the dispersive stress only proving significant for the coarsest material. DebrisLib had to use a modified version of the dispersive term to simulate these concentrations. Both the 2D depth-averaged shallow water equation (SWE) and diffusion wave equation were used to simulate the experiments. The best results were obtained with the SWE with horizontal mixing.     

鄱阳湖湖泊流域系统水文水动力联合模拟

本文以鄱阳湖湖泊流域系统为研究对象,鉴于该湖泊流域系统尺度较大,下垫面自然属性呈现高度空间异质性且具有流域-平原区-湖泊不同机制的水文水动力过程,为了真实描述湖泊流域间的水文水动力联系及反映不同过程间的作用机制,构建了鄱阳湖湖泊流域联合模拟模型.该模型基于自主研发的流域分布式水文模型WATLAC和湖滨平原区产流模型以及水动力模型MIKE 21 3个不同功能子模型的连接来实现该复杂系统的模拟.模型的联合采用输入-输出驱动及子模型的顺序执行进程,即将五大子流域与平原区入湖径流量作为输入条件来驱动湖泊水动力模型,模拟湖泊水位对流域入湖径流量的响应.以2000-2005年鄱阳湖流域6个水文站点的河道径流量、流域基流指数以及湖泊4个站点的水位资料来率定模型,其中各站点日径流量拟合的纳希效率系数E_ns为0.71~0.84,确定性系数R²介于0.70~0.88之间,而湖泊各站点水位拟合的纳希效率系数E_ns变化为0.88~0.98,确定性系数R²为0.96~0.98,均取得令人满意的率定结果.本文提出的鄱阳湖湖泊流域系统水文水动力联合模拟模型能较为理想再现湖泊水位对流域降雨-径流过程的响应.水位模拟结果进一步表明,该联合模型能用来获取重要的水动力空间变化特征.该模型可作为有效工具定量揭示湖泊流域系统水文水动力过程对气候变化和流域人类活动的响应.     

太湖不同湖区底泥悬浮沉降规律研究及内源释放量估算

太湖是一个大型浅水湖泊,湖湾、沿岸及湖心等区域受地形影响,湖流结构及水土界面水力要素均有显著差异.针对目前对不同湖区底泥再悬浮规律差异性研究的缺失,本研究选取了3个具有代表性的点采集太湖底泥,采用矩形水槽开展底泥再悬浮模拟实验,并结合太湖二维水量水质模型及太湖全年实测数据,建立了不同湖区底泥再悬浮通量与风速之间的定量关系;通过室内静沉降实验,得到了静沉降通量与风速的相关关系;最后将底泥再悬浮实验结果参数化应用于太湖二维水量水质模型中,并对底泥悬浮沉降过程进行分解和概化,估算太湖全年内源释放量.结果表明:太湖每日的内源释放量受风速影响显著,和风速变化趋势较为接近,太湖全年进入水体的净底泥量有47.81×104t,夏季最大,冬季次之;就营养物质释放量而言,COD约为2.06×104t、总氮约为1149.05 t、总磷约为564.35 t,其中秋季营养物质释放量最小,夏季最大.     

Chemical and isotopic assessment of surface water–shallow groundwater interaction in the arid Grande river basin,North-Central Chile

ABSTRACT

This paper analyses the composition of surface water and shallow groundwater in the Grande River basin, North-Central Chile, using this information to characterize water interactions. Chemical and isotopic data for surface water and groundwater (7 and 6 sampling locations, respectively) were obtained from three sampling campaigns performed in March–April (autumn), August–September (late winter) and December (early summer) 2012. Precipitation samples were also collected. Data was processed using spatial distribution charts, Piper and Stiff diagrams, and multivariate analysis. In general, the results for each method converge on a high degree of connectivity between surface water and shallow groundwater in the study area. Furthermore, approximately a 10% of groundwater contribution to the surface flow discharge was estimated for a particular reach. This multi-method approach was useful for the characterization of surface water–groundwater interactions in the Grande River basin, and may become a suitable and replicable scheme for studies in arid and semi-arid basins facing similar water management challenges.

Editor D. Koutsoyiannis; Associate editor B. Dewals     

Three-dimensional numerical modelling of wind-driven circulation in a homogeneous lake

A three-dimensional numerical model has been developed to study wind-induced circulation patterns in a shallow homogeneous lake with a complex bathymetry. The governing equations are the unsteady Reynolds-Averaged Navier–Stokes equations in which the non-hydrostatic pressure distribution has been included. The model was tested against analytical solutions and laboratory data for wind-induced currents and then applied to Esthwaite Water, a small lake in Cumbria, UK. The model was used to study the main model parameters and to generate typical circulation patterns for a variety of conditions in the lake. Simulations showed that a non-hydrostatic pressure distribution did not have any noticeable influence on the overall circulation pattern in the lake. However, comparisons with field data at some measurement stations in the near-shore region with sharply varying bottom topography showed that the hydrodynamic pressure component had some influence on the vertical velocity profile.     

盐度对湖冰冻结过程中氮磷营养盐排出效应的影响

伴随结冰过程的盐分排出是驱动冰封浅湖营养盐动态变化的关键过程,影响湖泊水质、环境与生态演变.为探究湖冰冻融过程如何改变寒区浅湖营养盐条件,采用自制定向冻结装置开展了无机氮磷营养盐溶液(NH₃-N、NO^-₂-N、NO^-₃-N、PO^3-₄-P)的室内冻结试验,结合现场采样分析评估了冻结排出效应对典型浅湖氮磷营养盐的影响.结果表明:营养盐浓度、盐度(以NaCl表征)是影响冻结排出效率的关键因素;随营养盐浓度的升高,冰内营养盐浓度升高,但冻结分离系数减小;若盐度升高,冰内营养盐浓度和分离系数均增大,主要与未冻卤水泡的形成有关;3种形态的无机氮、磷酸根的分离系数均存在明显差异.将试验结果应用于内蒙古乌梁素海结冰期氮磷营养分析,计算表明湖冰冻结排盐过程不仅造成湖水各类营养盐浓度升高,同时改变无机氮素构成、氮磷比等营养结构状态;特别是若湖泊盐度发生变化,氮磷营养盐的冻结排出效率及其差异性均会显著改变,增加冰封期湖泊营养条件的时空变异性.本文结果可广泛应用于定量评价冰层冻融过程对冬季湖泊营养条件的影响,有助于理解冰封期浮游植物群落演变的内在驱动力.     

Uncertainty propagation of hydrodispersive transfer in an aquifer: an illustration of one-dimensional contaminant transport with slug injection

It is evident that the hydrodynamic dispersion coefficient and linear flow velocity dominate solute transport in aquifers. Both of them play important roles characterizing contaminant transport. However, by definition, the parameter of contaminant transport cannot be measured directly. For most problems of contaminant transport, a conceptual model for solute transport generally is established to fit the breakthrough curve obtained from field testing, and then suitable curve matching or the inverse solution of a theoretical model is used to determine the parameter. This study presents a one-dimensional solute transport problem for slug injection. Differential analysis is used to analyze uncertainty propagation, which is described by the variance and mean. The uncertainties of linear velocity and hydrodynamic dispersion coefficient are, respectively, characterized by the second-power and fourth-power of the length scale multiplied by a lumped relationship of variance and covariance of system parameters, i.e. the Peclet number and arrival time of maximum concentration. To validate the applicability for evaluating variance propagation in one-dimensional solute transport, two cases using field data are presented to demonstrate how parametric uncertainty can be caught depending on the manner of sampling.     

Impact of the sampling duration on the uncertainty of averaged velocity measurements with acoustic instruments

Average velocity in streams is a key variable for the analysis and modelling of hydrological and hydraulic processes underpinning water resources science and practice. The present study evaluates the impact of the sampling duration on the quality of average velocity measurements acquired with contemporary instruments such as Acoustic Doppler Velocimeters (ADV) an Acoustic Doppler Current Profilers (ADCP). The evaluation combines considerations on turbulent flows and principles and configurations of acoustic instruments with practical experience in conducting customized analysis for uncertainty analysis purposes. The study sheds new insights on the spatial and temporal variability of the uncertainty in the measurement of average velocities due to variable sampling durations acting in isolation from other sources of uncertainties. Sampling durations of 90 and 150 s are found sufficient for ADV and ADCP, respectively, to obtain reliable average velocities in a flow affected only by natural turbulence and instrument noise. Larger sampling durations are needed for measurements in most of the natural streams exposed to additional sources of data variability.     

Reliability assessment of water structures subject to data scarcity using the SCS-CN model

ABSTRACT

When discharge measurements are not available, design of water structures relies on using frequency analysis of rainfall data and applying a rainfall–runoff model to estimate a hydrograph. The Soil Conservation Service (SCS) method estimates the design hydrograph first through a rainfall–runoff transformation and next by propagating runoff to the basin outlet via the SCS unit hydrograph (UH) method. The method uses two parameters, the Curve Number (CN) and the time of concentration (T_c). However, in data-scarce areas, the calibration of CN and T_c from nearby gauged watersheds is limited and subject to high uncertainties. Therefore, the inherent uncertainty/variability of the SCS parameters may have considerable ramifications on the safety of design. In this research, a reliability approach is used to evaluate the impact of incorporating the uncertainty of CN and T_c in flood design. The sensitivity of the probabilistic outcome against the uncertainty of input parameters is calculated using the First Order Reliability Method (FORM). The results of FORM are compared with the conventional SCS results, taking solely the uncertainty of the rainfall event. The relative importance of the uncertainty of the SCS parameters is also estimated. It is found that the conventional approach, used by many practitioners, might grossly underestimate the risk of failure of water structures, due to neglecting the probabilistic nature of the SCS parameters and especially the Curve Number. The most predominant factors against which the SCS-CN method is highly uncertain are when the average rainfall value is low (less than 20 mm) or its coefficient of variation is not significant (less than 0.5), i.e. when the resulting rainfall at the design return period is low. A case study is presented for Egypt using rainfall data and CN values driven from satellite information, to determine the regions of acceptance of the SCS-CN method.

EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR A. Efstratiadis     

Low-cost inundation modelling at the reach scale with sparse data in the Lower Damodar River basin,India

Abstract

Data unavailability is the main reason for limited applications of hydrodynamic models for predicting inundation in the developing world. This paper aims to generate moderately high-resolution hybrid terrain data by merging height information from low-cost Indian Remote Sensing satellite (IRS) Cartosat-1 stereo satellite images, freely-available Shuttle Radar Topograph Mission (SRTM) digital elevation model (DEM) data, and limited surveyed channel cross-sections. The study reach is characterized by anabranching channels that are associated with channel bifurcation, loops and river islands. We compared the performance of a simple 1D–2D coupled LISFLOOD-FP model and a complex fully 2D finite element TELEMAC-2D model with the hybrid terrain data. The results show that TELEMAC-2D produced significantly improved simulated inundation with the hybrid terrain data, as compared to the SRTM DEM. LISFLOOD-FP was found unsuitable to work with the hybrid DEM in a complicated fluvial environment, as it failed to efficiently divert water in the branches from the main channel.

Editor D. Koutsoyiannis; Associate editor A. Viglione     

Assessing vertical diffusion in a stratified lake using a three-dimensional hydrodynamic model

Vertical turbulent diffusivity (K_z), which can be estimated from water temperature, is a key factor in the evolution of water quality in lentic waters. In this study, we analysed the capability of a three-dimensional hydrodynamic model (EFDC) to capture water temperature and vertical diffusivity in Lake Arendsee in the Northern German plain. Of particular interest to us is to evaluate the model performance for capturing the diffusion minimum within the metalimnion and analyse the response of the metalimnetic K_z to meteorological forcing, namely changing wind speed and warming. The comparison confirmed that the calibrated model could reproduce both stratification dynamics and vertical diffusion profiles in the lake. The model was also shown to be able to capture the duration and vertical extent of the metalimnetic diffusion minimum. The scenario results illustrate that, compared to air temperature, wind velocity appeared to be the more influential meteorological variable on the vertical exchange within the metalimnion. While increasing wind velocities mostly affected the minimum values of K_z in the metalimnion and thus led to intensified vertical exchange, the reduction of wind velocity mostly affected the depth of minimal K_z, but not its absolute value.     

基于频谱分析的水体波浪—紊动流速分离方法

根据波浪影响下水质点运动速度的频谱分布特征,本文提出了一种用于分离水体波浪轨道流速与紊动流速的分离方法.该方法仅需通过一台流速仪对水体瞬时流速进行高频测量,便可对水体波浪—紊动流速进行分离,实现受波浪影响水体的紊动分析.通过验证,频谱分析法不仅能够用于实验室中规则波浪条件下水体波浪—紊动流速的分离,还能够对野外不规则波...     

Model of Formation and Development of Spring Thermal Bar

A mathematical model simulating the thermo- and hydrodynamic processes near the thermal bar in the period of lake warming in spring is considered. A closed system of Reynolds type equations is constructed based on the Navier–Stokes nonlinear system of equations using the Boussinesq approximation and a special technique for isolating large-scale structures in turbulent medium. The turbulent viscosity coefficient is evaluated in the course of problem solution. The results of calculations are shown to agree well with field observation data.     

一种浅水湖耦合模式系统的发展与应用

Growing developments in lake basins in China, have adversely affected, the water quality of lake, in particular, the water bodies of many famous shallow lake are seriously polluted in recent years. Some projects have been built up to improve the water quality, for example, the sewage interception project (i.e. Xiyuan tunnel project) and four sewage treatment plants etc. have been built up in Dianchi Lake. In order to predict and evaluate the effects of projects on the water quality, it is necessary to develop a coupled model system, which should mainly include wind, circulation and water quality parameters. This paper describes the development and application of a coupled modeling system in a shallow lake, which include a 3D micro-meteorology model (3DMM), a 2D hydrodynamic model (2DHM) and a 2D water quality model(2DWM).The coupled modeling system has been applied to predict the ejfects of environmental protection projects on water quality in Dianchi Lake.     

Simulation of vertical position of buoyancy regulating Microcystis aeruginosa in a shallow eutrophic lake

Vertical distributions of the cyanobacterium Microcystis aeruginosa are examined in a shallow lake in relation to mixing and thermal stratification over three days. A model of buoyancy regulation by Microcystis aeruginosa, applicable for turbulent environments, is coupled with a one-dimensional hydrodynamic model. The coupled model is applied to Thomsons Lake in Western Australia to examine the relationship between buoyancy regulation and the daily stratification/destratification cycle. The vertical distribution of Microcystis aeruginosa in Thomsons Lake depends on the carbohydrate ballast dynamics and the colony size. When thermal stratification occurs, all the simulations show a similar general pattern of diurnal vertical migration of the Microcystis aeruginosa colonies. The colonies accumulate at the surface during the night and in the morning the colonies lose buoyancy, which leads to a reduction by ~ \sim 50% in colony concentration in the top 0.2--0.3 m of the water column. Afternoon winds redistribute the population over the entire water column. When the lake is fully mixed, the vertical migration pattern of the Microcystis aeruginosa colonies may be affected, depending on the colony size and the intensity of the mixing.     

Accuracy,reproducibility and sensitivity of acoustic Doppler technology for velocity and discharge measurements in medium-sized rivers

Abstract

With increased interest and requirements in surface water quality and hydrodynamics, additional information is needed about water flow in streams. The mobile OTT Qliner with acoustic Doppler technology (ADQ) provides a highly efficient and accurate way of collecting this information. For this study we completed 366 measurements of flow velocity, water depth and discharge with ADQ from September 2010 to June 2011 at 174 cross-sections in eight catchments of different sizes located in northern Germany, central Germany and southeastern China. The measurements were used to study the accuracy, reproducibility and sensitivity of the device, and to improve the hydrodynamic sampling for medium-sized rivers and channels by investigating its internal settings. The observations reported clearly show that the results of flow average, profile, layer and point values obtained with the ADQ compare very well with those of electromagnetic or ultrasonic devices. In general, the average flow velocity gives the highest agreement. Vertical velocity has a better quality than the layer velocity, which indicates a greater precision in the horizontal than in the perpendicular direction. Point velocity, the composite of vertical velocity and layer velocity, has intermediate precision. Tests on internal settings revealed that measurement is more sensitive to cell size than to time interval setting. A cell size to depth ratio of between 0.1 and 0.2 m produced the highest reliability. A measurement period of 30 s is needed for velocities faster than 0.3 m/s; for shallow and slow-flowing rivers, an interval of 50 s or even greater is recommended. The closer the measured points were to the river bank or bed, the greater the measurement error. The river bed can also influence the measurement more distinctly than the river bank.

Editor D. Koutsoyiannis; Associate editor A. Montanari

Citation Song, S., Schmalz, B., Hörmann, G., and Fohrer, N., 2012. Accuracy, reproducibility and sensitivity of acoustic Doppler technology for velocity and discharge measurements in medium-sized rivers. Hydrological Sciences Journal, 57 (8), 1626–1641.