Simulation of the Hydrodynamic Functioning of the Cavally River Using a Coupled 1D-2D Model in the Ity Area (Zouan-Hounien in Côte d’Ivoire)

In recent years, the Cavally River has been subject to multiple activities, including the construction of diversion channels and a bridge that makes it vulnerable to flooding. In order to assess the impact of these hydraulic structures on the river hydrodynamic functioning, a 1D-2D model was realized. The implementation of the 1D-2D model consisted of first running the 1D model, then the 2D model, and finally in coupling them. The 1D-2D model was designed with the 1988 flood hydrograph, a Manning’s coefficient of 0.052 m1/3/s for the minor bed and 0.06 m1/3/s for the major bed. The results of the hydraulic model show that the velocities are almost identical to those of the Cavally in natural operation. The values of the velocities are included between 0.4 m/s and 1.3 m/s at the level of the minor bed of the river and between 0.06 m/s and 0.71 m/s at the level of the floodplains. The average water level for flood propagation is 262.37 ± 0.44 m before construction of the structures and 262.23 ± 0.85 m after construction of the structures. The 0.41 m reduction in water level due to the diversion canal and bridge is negligible compared to the total fluctuations of the Cavally River, which vary from 6 to 7 m over the year.

An Implicit Coupled 1D/2D Model for Unsteady Subcritical Flow in Channel Networks and Embayment

In this study, 1D and 2D shallow-water models were coupled to simulate unsteady flow in channel networks and embayment. The 1D model solved the 1D shallow-water equations (St. Venant) using the Preissmann box method and targeted long narrow reaches of the river networks, while the 2D model targeted broad channels and embayment and solved the 2D shallow-water equations using a semi-implicit scheme applied to an unstructured grid of triangular cells. The 1D and 2D models were solved simultaneously by building a matrix for the free surface elevation at every 1D junction and 2D cell center. Velocities were then computed explicitly based on the results at the previous time step and the updated water level. The originality of the scheme arose from a novel coupling method. The results showed that the coupled 1D/2D model produced identical results as the full 2D model in classical to benchmark problems with considerable savings in computational effort. Application of the model to the Pearl River Estuary in southern China showed that complex patterns of tidal wave propagation could be efficiently modeled.

Mathematical model for flood routing in Jingjiang River and Dongting Lake network

The main stream of the Yangtze River, Dongting Lake, and the river network in the Jingjiang reach of the Yangtze River constitute a complex water system. This paper develops a one-dimensional （l-D） mathematical model for flood routing in the river network Of the Jingjiang River and Dongting Lake using the explicit finite volume method. Based on observed data during the flood periods in 1996 and 1998, the model was calibrated and validated, and the results show that the model is effective and has high accuracy. In addition, the one-dimensional mathematical model for the river network and the horizontal two-dimensional （2-D） mathematical model for the Jingjiang flood diversion area were coupled to simulate the flood process in the Jingjiang River, Dongting Lake, and the Jingjiang flood diversion area. The calculated results of the coupled model are consistent with the practical processes. Meanwhile, the results show that the flood diversion has significant effects on the decrease of the peak water level at the Shashi and Chenjiawan hydrological stations near the flood diversion gates, and the effect is more obvious in the downstream than in the upstream.

Integrating 1D and 2D hydrodynamic,sediment transport model for dam-break flow using finite volume method

The purpose of this study is to set up a dynamically linked 1D and 2D hydrodynamic and sediment transport models for dam break flow.The 1D-2D coupling model solves the generalized shallow water equations,the non-equilibrium sediment transport and bed change equations in a coupled fashion using an explicit finite volume method.It considers interactions among transient flow,strong sediment transport and rapid bed change by including bed change and variable flow density in the flow continuity and momentum equations.An unstructured Quadtree rectangular grid with local refinement is used in the 2D model.The intercell flux is computed by the HLL approximate Riemann solver with shock captured capability for computing the dry-to-wet interface for all models.The effects of pressure and gravity are included in source term in this coupling model which can simplify the computation and eliminate numerical imbalance between source and flux terms.The developed model has been tested against experimental and real-life case of dam-break flow over fix bed and movable bed.The results are compared with analytical solution and measured data with good agreement.The simulation results demonstrate that the coupling model is capable of calculating the flow,erosion and deposition for dam break flows in complicated natural domains.

A COUPLED 1-D AND 2-D CHANNEL NETWORK MATHEMATICAL MODEL USED FOR FLOW CALCULATIONS IN THE MIDDLE REACHES OF THE YANGTZE RIVER

A coupled one-dimensional （1-D） and two-dimensional （2-D） channel network mathematical model is proposed for flow calculations at nodes in a channel network system in this article. For the 1-D model, the finite difference method is used to discretize the Saint-Venant equations in all channels of a looped network. The Alternating Direction Implicit （ADI） method is adopted for the 2-D model at the nodes. In the coupled model, the 1-D model provides a good approximation with small computational effort, while the 2-D model is applied for complex topography to achieve a high accuracy. An Artificial Neural Network （ANN.） method is used for the data exchange and the connectivity between the 1-D and 2-D models. The coupled model is applied to the Jingjiang-Dongting Lake region, to simulate the tremendous looped channel network system, and the results are compared with field data. The good agreement shows that the coupled hydraulic model is more effective than the conventional 1-D model.

ONE-AND TWO-DIMENSIONAL COUPLED HYDRODYNAMICS MODEL FOR DAM BREAK FLOW

1-D and 2-D mathematical models for dam break flow were established and verified with the measured data in laboratory. The 1-D and 2-D models were then coupled, and used to simulate the dam break flow from the reservoir tail to the dam site, the propagation of dam break waves in the downstream channel, and the submergence of dam break flow in the downstream town with the hydrodynamics method. As a numerical example, the presented model was employed to simulate dam break flow of a hydropower station under construction. In simulation, different dam-break durations, upstream flows and water levels in front of dam were considered, and these influencing factors of dam break flow were analyzed, which could be referenced in planning and designing hydropower stations.

基于一二维耦合模型和水库调度的长江宜宾河段洪水遭遇与淹没分析

【目的】宜宾市地处金沙江与岷江汇合处,且有横江、南广河及其他重要支流汇入,因此洪水遭遇组合复杂,且受金沙江下游向家坝-溪洛渡等梯级水库调度影响明显,其水文水动力计算对下游各城镇河段防洪规划及减灾政策制定具有重要意义。【方法】通过构建一二维水动力学耦合数学模型,采用实测洪水验证的分析方法对长江宜宾河段(含重要支流汇入段)的洪水组合进行分析,选取了1961年、1966年两个典型年并对比有无金沙江下游梯级水库调洪的影响,计算各河段和沿岸城镇100 a、50 a及20 a一遇的洪水淹没。【结果】结果表明:(1)当发生超标洪水时,城区主要洪水漫溢淹没分布在宜宾的安边镇、柏溪街道,翠屏区西郊街道以及岷江菜坝镇飞机坝段。(2)不管是1961典型年(岷江为主要来水)还是1966典型年(金沙江为主要来水),岷江流域均受灾较重;其中西郊街道和大观楼街道的洪水主要受金沙江来水和岷江洪水顶托作用明显;岷江漫溢洪水为宜宾城区外洪的主要来源,岷江是宜宾市的防洪重点。【结论】结合防洪工程分布及现有堤防建设情况,菜坝镇飞机坝片区现有的20 a一遇洪水的堤防无法满足实际防洪标准需求;西郊街道滨江公园和备战码头,由于未形成防洪封闭圈,城区局部地区仍处于不设防状态;柏溪镇堤防防洪标准20 a一遇偏低,黑河(柏树溪)受到金沙江回水影响会造成柏溪镇严重洪灾。金沙江在向家坝水库的调蓄作用下,即使发生100 a或超过50 a一遇超标洪水,中心城区均不超过40 a一遇,宜宾城区受金沙江洪水影响相对较小,受岷江回水影响较大。

热污染的一、二维耦合模型及其应用

滨海、河口二个火电站并存时 ,其冷却水所释放的热量常造成周围水体的温度上升并相互干扰、叠加。它们之间的水体、温度相互流动、渗混 ,交接点上的水位、流速及温升同时满足一、二维方程 ,为此必须进行耦合解。本文提供了一、二维任意交角普遍性的耦合解法 ,并应用北仑、镇沦二个火电站之间的热污染计算为实例 ,求得了它们相互影响的定量值。

飞来峡水利枢纽库区动态纳污能力计算研究

根据飞来峡水利枢纽库区水流及水质特点,选取不同设计流量,建立二维水流水质模型.通过水槽实验,拟合水质衰减系数与流速的关系曲线,以获取模型水质计算参数.研究结果表明：通过概化排污口排污量与混合带长度响应关系计算,确定各排污口混合带长度在1 300～2 500m之间;在90％最枯月、50％最枯月及多年平均流量水文条件下,飞来峡库区干流水域COD纳污能力分别为162 107.7t、199 220.2t及372 104.3t; NH3-N纳污能力分别为2 757.4t、3 408.4t和6 276.4t;飞来峡库湾的纳污能力远小于库区干流水域,库湾COD纳污能力仅相当于干流的25％,NH3-N纳污能力仅相当于干流的5％;飞来峡库区纳污能力年内逐月差异显著,其中汛期（4～9月）纳污能力较大,COD、NH3-N纳污能力约占全年纳污能力的58％,飞来峡库区年内月纳污能力与月平均流量呈现较好的正相关关系.

西三洼洪水演进数值模拟及洪水风险分析

为模拟西三洼蓄滞洪区洪水演进,对其洪水风险进行分析,以一、二维非恒定流控制方程为基本理论,采用有限体积法,结合西三洼地形资料及大清河流域水文资料,建立一、二维耦合的洪水演进数学模型。采用63·8洪水实测资料对模型进行验证,结果基本吻合。对不同工况及重现期下的设计洪水进行洪水演进模拟计算并绘制洪水风险图。研究表明:该模型可模拟西三洼蓄滞洪区各分洪口门开扒时间、各时刻淹没面积、淹没水深及滞洪量等水情信息及其变化过程;规划情况(增加安全区)的滞洪总量大于现状情况滞洪总量;发生百年一遇洪水时,西三洼蓄滞洪区77%地区都遭受洪水侵害,其中57%区域为危险区,11%区域为重灾区,5%区域为中灾区。研究成果可为防汛部门制定科学合理的防洪减灾规划提供参考依据。

动态纳污能力计算方法与应用研究

通过环境水槽实验获取了COD和NH3-N衰减系数与流速效应之间的定量关系式,建立了反应污染物衰减与流速动态变化的二维水流水质数学模型。以广东省飞来峡水利枢纽库区为例,利用二维水流水质数学模型和常规的完全混合模型对库区COD和NH3-N纳污能力进行了计算。结果表明:前者计算的纳污能力大于后者,其计算出的主流区纳污能力为库湾区的8.4倍左右。分析认为二维水流水质数学模型计算结果更符合实际。

一、二维耦合数学模型在感潮河网洪水风险图编制中的应用

为了解决感潮河网径流、潮汐交汇,动力复杂,溃决洪水难以用经验公式准确概化的问题,建立直接以溃口为耦合断面的河网一维、保护区二维侧向耦合模型,将感潮河网与保护区一体化,避免环境因素及经验参数的不确定性带来的溃口流量估算误差。典型算例和中顺大围溃决洪水情景模拟表明:洪水自溃口集中喷射出后分散流向围内,流态受围内下垫面影响显著,溃口水位、流量随外江潮位涨落而起伏变化,由溃口流量过程线计算所得溃口水量与根据淹没区各单元的面积和水深计算的围内总水量一致。模拟成果直接反映下垫面、水头差、潮位涨落,及溃口流态对溃决洪水的综合影响,反映出本耦合模型计算溃口流量及对溃决洪水模拟的合理性、可信性,具有较好的应用前景。

陆面-河网耦合模型在极端风暴潮淹没危险性分析中的应用

在风暴潮灾害中,台风、天文高潮位、区间暴雨和上游洪水等因子存在同时出现的可能,对沿海地区的防汛安全形成了较为严重的威胁.双因子、多因子影响下的复合风暴潮灾害成为沿海地区灾害风险评估的主要研究对象.风暴潮水通过漫堤和溃口进入陆域后,河网对潮水的调蓄和运输作用直接影响对受灾区域灾害危险性的评估结果.本研究选取上海市金山区作为典型区域,基于MIKE11和MIKE21模型分别建立金山区一维河网模型和二维陆面模型,并进行耦合计算,模拟分析在风暴潮、台风、区间暴雨和流域洪水的综合影响下,金山区地面积水变化过程,为区域的灾害危险性分析提供依据.模型计算结果表明,在考虑陆域河网调蓄作用后,风暴潮引起的金山区地面积水大幅度减小,区域内整体淹没分布出现一定程度的改变.综合考虑风暴潮及区间暴雨和流域洪水与仅考虑风暴潮条件相比,金山区中部和北部大部分区域危险性等级降低,西北角危险性等级升高.

北部湾及广西近海潮流数值模拟

该文采用二维浅水模型模拟分析了北部湾海域潮流系统,并在此基础上建立了广西沿海一、二维耦合水动力模型,模型中考虑了广西沿岸6条主要入海河流对近岸水动力的影响,进一步分析了广西近海海域潮致余流场及其对近海污染物输移扩散的影响。模型潮位计算值和实测值符合良好。结果显示:K1分潮在北部湾口形成一个逆时针旋转潮波系统,M2分潮在湾顶越南海防附近形成逆时针旋转潮波系统,广西近海海域K1分潮占优。广西沿海海域内,离岸较近的海域余流场相对较强,余流速度受浅水效应及湾口等地形缩窄影响而增强;离岸较远海域余流明显减弱,水体交换能力降低。