Parameter Estimation in Water Distribution Networks

Estimation of pipe roughness coefficients is an important task to be carried out before any water distribution network model is used for online applications such as monitoring and control. In this study, a combined state and parameter estimation model for water distribution networks is presented. Typically, estimation of roughness coefficient for each individual pipe is not possible due to non-availability of sufficient number of measurements. In order to address this problem, a formal procedure based on K-means clustering algorithm is proposed for grouping the pipes which are likely to have the same roughness characteristics. Also, graph-theoretic concepts are used to reduce the dimensionality of the problem and thereby achieve significant computational efficiency. The performance of the proposed model is demonstrated on a realistic urban water distribution network.     

Establishing a Multi-scale Stream Gaging Network in the Whitewater River Basin,Kansas, USA

Investigating the routing of streamflow through a large drainage basin requires the determination of discharge at numerous locations in the channel network. Establishing a dense network of stream gages using conventional methods is both cost-prohibitive and functionally impractical for many research projects. We employ herein a previously tested, fluid-mechanically based model for generating rating curves to establish a stream gaging network in the Whitewater River basin in south-central Kansas. The model was developed for the type of channels typically found in this watershed, meaning that it is designed to handle deep, narrow geomorphically stable channels with irregular planforms, and can model overbank flow over a vegetated floodplain. We applied the model to ten previously ungaged stream reaches in the basin, ranging from third- to sixth-order channels. At each site, detailed field measurements of the channel and floodplain morphology, bed and bank roughness, and vegetation characteristics were used to quantify the roughness for a range of flow stages, from low flow to overbank flooding. Rating curves that relate stage to discharge were developed for all ten sites. Both fieldwork and modeling were completed in less than 2 years during an anomalously dry period in the region, which underscores an advantage of using theoretically based (as opposed to empirically based) discharge estimation techniques.     

含竖向杆件的半圆形明渠糙率研究

TBM掘进机轨道常采用工字钢支撑,明渠底部设置工字钢后会降低其过水能力。为了定量研究明渠底部设置工字钢后对其糙率的影响,引入了等效水力参数的概念,对工字钢产生的等效附加糙率进行了理论分析。此外,结合某实际工程,通过模型试验研究,测量了设有工字钢的半圆形明渠在不同流量下的水深,采用假定糙率试算法、逐段计算糙率法对其综合糙率进行了计算分析。研究结果表明,建立的"糙率条带计算法+等效附加糙率计算法"得到的综合糙率值与模型试验值吻合良好,可采用理论计算方法估算半圆形明渠底部设置竖向杆件后的综合糙率。     

粒子群算法在河道水动力模型参数校正中的应用

参数估计一直是河道水动力模型研究的难点之一,在传统的模型参数人为经验率定方法的基础上,提出了基于粒子群算法的模型参数优化校正方法,构建了参数校正优化模型,并将参数优化校正算法与河道水动力模型进行耦合,针对淮河干流和史灌河支流组成的研究区域,采用一维河道洪水演进模型,比较了糙率系数校正方法和传统经验估算法,校正方法得到的河段糙率系数值比人为经验估计值平均大0.01,淮河干流河段糙率略大于史灌河支流河段糙率,采用校正河段糙率系数得到的河道水位过程与实测值拟合更优,特别在主峰段洪水过程模拟精度显著改善,验证了本文所提出的参数优化校正算法的有效性,为复杂河道水动力模型参数的确定提供了一种有效方法。     

Roughness coefficient and its uncertainty in gravel-bed river

Manning's roughness coefficient was estimated for a gravel-bed river reach using field measurements of water level and discharge,and the applicability of various methods used for estimation of the roughness coefficient was evaluated.Results show that the roughness coefficient tends to decrease with increasing discharge and water depth,and over a certain range it appears to remain constant.Comparison of roughness coefficients calculated by field measurement data with those estimated by other methods shows that,although the field-measured values provide approximate roughness coefficients for relatively large discharge,there seems to be rather high uncertainty due to the difference in resultant values.For this reason,uncertainty related to the roughness coefficient was analyzed in terms of change in computed variables.On average,a 20%increase of the roughness coefficient causes a 7% increase in the water depth and an 8% decrease in velocity,but there may be about a 15% increase in the water depth and an equivalent decrease in velocity for certain cross-sections in the study reach.Finally,the validity of estimated roughness coefficient based on field measurements was examined.A 10% error in discharge measurement may lead to more than 10% uncertainty in roughness coefficient estimation,but corresponding uncertainty in computed water depth and velocity is reduced to approximately 5%.Conversely,the necessity for roughness coefficient estimation by field measurement is confirmed.     

人工渠道糙率系数影响因素的试验研究

通过物理模型试验资料分析,探讨了矩形渠道的糙率与渠道水深、弗汝德数的变化规律。分析得出:当底坡不变时,随着弗汝德数Fr的增大,糙率n值逐渐减小。在缓流渠道中,渠道糙率n随弗汝德数Fr变化的速率很快;在急流渠道中,渠道糙率n值随弗汝德数Fr的速率较慢。糙率系数n随水深h的变化关系与流态有关。缓流中,随着水深h的增大,糙率n值减小;急流中,当弗汝德数11.51时,糙率系数n随水深h的增大而增大。     

含淹没植被明渠水位及糙率变化试验研究

采用概化水槽试验研究了在不同植物间距、水流条件下,含淹没植被明渠水位、曼宁糙率系数的变化特征,给出了含淹没植被明渠的糙率经验公式.试验结果表明:相同的流量、水深条件下,明渠的水位壅高值和水面比降均随植物间距的减小而逐渐增大,当植物枝叶相互间贴近或交叉时,植物对明渠水位、比降的影响程度相对较大;水深基本相同、植物排列方式相同的情况下,随着流量的增加,水面比降基本呈线性增大趋势;水深相同的条件下,含淹没植被明渠糙率受水流流速的影响较小.     

耦合渗漏项的季节性河道洪水演进模型研究

针对北方干旱或半干旱区季节性河道渗漏现象严重问题,为提高流域洪水演进模拟精度,在传统水动力学洪水演进模型基础上耦合河道渗漏项,构建季节性河流洪水演进数学模型。采用霍顿入渗模型描述季节性河道渗漏过程,解决河道渗漏量计算及与基于圣维南方程组洪水演进模型耦合问题;并利用Preissmann四点偏心隐格式与追赶法对模型离散和计算,开发FORTRAN计算程序;最后以大沽河流域实测资料进行验证。结果表明,沙湾庄和南村断面水位与流量过程的模拟值与实测值吻合且变化趋势一致,洪水峰面到达断面模拟时间和实际时间基本一致,研究区各河段来水量、渗漏量的实测值与模拟值相对误差范围分别为-1.66%~0.36%、-3.09%~3.72%,所建模型可满足在现状条件下进行洪水模拟预报的需要。     

A Distributed Kinematic Wave–Philip Infiltration Watershed Model Using FEM,GIS and Remotely Sensed Data

Distributed rainfall–runoff modeling is very important in the water resources planning of a watershed. In this study, a kinematic wave based distributed watershed model which simulates runoff on an event basis has been presented here. The finite element method (FEM) has been used to simulate the overland runoff and channel flow. Philip model has been used for the infiltration estimation. To find out runoff at the outlet of the watershed, both overland flow and channel flow models are coupled. The coupled model has been applied to a typical Indian watershed. Remotely sensed data has been used to obtain the land use (LU)/land cover (LC) for the watershed. Slope map of the watershed has been obtained using geographical information systems (GIS). The grid map of the watershed which contains overland flow elements connecting to channel flow elements has been prepared in GIS. The elemental input files such as slope and Manning’s roughness are prepared using the GIS and are directly used in the model. The model has been calibrated using some of the rainfall events and validated for some other events. The model results are compared with the observed data and found to be satisfactory. A sensitivity study of the infiltration parameters, overland and channel flow Manning’s roughness and time step has also been carried out. The developed model is useful for the simulation of event based rainfall–runoff for small watersheds.     

基于 MIKE21 FM 的南渡江河口段行洪能力分析

为预测并分析滨江西带状公园建设后对南渡江河口段行洪能力的影响,基于MIKE21FM水动力模块,建立了南渡江河口段平面二维水流数值模型。首先结合水文站实测洪水资料,对河口段河道、滩地糙率参数进行率定与验证。将公园模型概化为局部阻力修正和局部地形修正两种方式,然后分别模拟计算三种潮洪组合工况下河口段水面线和流场变化。计算结果表明,两种概化方式计算结果基本一致,公园建设后河道地形和糙率发生变化,导致水面线壅高和主流流速加大。阻力修正法计算的水面线壅高值稍偏大,但仍低于左右岸防洪堤设计水位,没有降低南渡江河口段防洪能力。司马坡岛附近局部出现高流速区,有必要采取相应的防冲措施。     

混凝土渠道糙率调研综述

在查阅大量资料以及考察国内十几个大型输水工程并与各地专家及技术人员进行广泛交流的基础上,对混凝土渠道糙率的设计情况与实测资料进行综述,并作了初步分析。分析结果表明：对于能基本保持设计条件的渠道,其实际水头损失小于设计值,对于施工质量较好的现浇混凝土渠道,其均匀流段的曼宁糙率系数不大于0013。同时,给出了不同衬砌特性的混凝土渠道糙率推荐表。     

Seasonality of Roughness - the Indicator of Annual River Flow Resistance Condition in a Lowland Catchment

Accurate estimation of flow resistance restricts the quality of the hydraulic model performance. In this study, we try to investigate the seasonal dynamic of the Manning’s roughness coefficient (n) based on the one-dimensional hydraulic model HEC-RAS in a German lowland area. We set up four river section models based on the 1 m digital elevation model and field measurements, in which the seasonal roughness factors were calibrated and validated with the gauge record. The results revealed that: 1) the Manning’s n varied from 46% to 135% from the base value in autumn; 2) adopting the seasonal roughness factor improved the quality of the model output; 3) the vegetation condition and water elevation dominated the Manning’s n in summer (April–September) and winter (October–March) half year respectively. Water temperature increased the flow resistence in winter half year; 4) the peak value of Manning’s n appeared in late summer due to the highest biomass, while the minimum roughness occurred in early-spring because of the combined influence of low biomass, high water level and relatively higher temperature. The involvement of seasonal roughness factor improved the model performance and the results are comparable to the previous research of the same area.     

河岸与河底相对粗糙度对河道平衡形态的影响研究

边界条件对河流地貌形态具有重要影响,基于河道边界阻力水力半径分割方法,利用变分方法研究河岸与河底相对粗糙度对冲积河流平衡河道形态的影响.结果表明,河岸与河底相对粗糙度对河流达到平衡时的最大输沙率有一定的影响,但对河道平衡形态的影响非常显著.在临界和平均水力几何形态关系式中,随着河岸与河底相对粗糙度的增大,河宽关系式的系...     

EXPERIMENTAL STUDY HYDRAULIC ROUGHNESS FOR KAN TIN MAIN DRAINAGE CHANNEI IN HONG KONG

The Kam Tin Main Drainage Channel (KTMDC) is an important river for the city drainage in Hong Kong. The roughness and its variations have an obvious effect on the flood control capacity and the flow capacity. So physical model tests are designed to study the KTMDC. Due to its complex channel structure, the tests are completed in two steps. In Step 1, the energy loss is measured along the main channel without inflows, with all inflows and outflows being sealed. In Step 2, all the inflow and outflow structures are measured, with the sealed inflows and outflows being opened on the basis of Step 1. In each step, two schemes are employed. One of the key issues is the choice of suitable materials to make the model’s roughness similar to that of the prototype. According to the gravity similarity criterion, the 1:25 scale model is built, with the main channel made of Perspex. The facing slopes of the grasscrete and the stone masonry need to be roughened. A kind of the nylon net is selected to simulate the roughness of the stone masonry and the plastic lawn for the grasscrete facing slope. For the different structure reaches, the roughness coefficients are estimated based on the hydraulic theory. The rationality of the test results is verified in this study. The results of testing can provide a reliable basis for the renovation, the expansion, the optimization of this channel.     

用模拟退火算法估计水质模型参数

本文采用BOD-DO耦合模型模拟水质。在获取参数最优化值时采用BOD和DO耦合模型计算值与实测值之差的加权平方和作为目标函数，将模拟退火算法(Simulated Annealing, SA)应用到多河段水质模型的多参数的同时估值中。采用30次重复估值试验，并记录所有试验中最优估计值的最大值和最小值，所得到的各河段BOD衰减系数的最优估值与真值的误差和河水复氧系数的最优估值与真值的误差均在允许范围内。说明了方法的可靠性。     

Dynamic Optimal Monitoring Network Design for Transient Transport of Pollutants in Groundwater Aquifers

Optimal groundwater pollution monitoring network design models are developed to prescribe optimal and efficient sampling locations for detecting pollution in groundwater aquifers. The developed methodology incorporates a two dimensional flow and transport simulation model to simulate the pollutant concentrations in the study area. Different realizations of the pollutant plume are randomly generated by incorporating the uncertainty in both source and aquifer parameters. These concentration realizations are incorporated in the optimal monitoring network design models. Two different objectives are considered separately. The first objective function minimizes the summation of unmonitored concentrations at different potential monitoring locations. This objective function in effect minimizes the probability of not monitoring the pollutant concentrations at those locations where the probable concentration value is large. Although this probability is not explicitly incorporated in the model, a surrogate form of this objective is included as the objective function. The second objective function considered is the minimization of estimation variances of pollutant concentrations at various unmonitored locations. This objective results in a design that chooses optimal monitoring locations where the uncertainties in simulated concentrations are large. The developed optimization models are solved using Genetic Algorithm. The variances of estimated concentrations at potential monitoring locations are computed using the geostatistical tool, kriging. The designed monitoring network is dynamic in nature, as it provides time varying network designs for different management periods, to account for the transient pollutant plumes. Such a design can eliminate temporal redundancy and is therefore, economically more efficient. The optimal design incorporates budgetary constraints in the form of limits on the number of monitoring wells installed in any particular management period. The solution results are evaluated for an illustrative study area comprising of a hypothetical aquifer. The performance evaluation results establish the potential applicability of the proposed methodology for optimal design of the dynamic monitoring network for detection and monitoring of pollutant plumes in contaminated aquifers.     

矩形渠道人工加糙壁面阻力规律试验研究

为研究矩形渠道水流的阻力规律,采用了3种不同粗糙度的人工加糙渠道进行试验。研究结果表明在均匀流条件下,对同一粗糙度明渠,水力条件变化时糙率系数不是恒定不变的,它会随着流量的加大而呈对数减小,随着渠道宽深比的增大而呈对数增大,同时随着雷诺数Re和弗汝德数Fr的增加而呈幂函数减小。同时表明,不同的壁面粗糙度对糙率系数影响很大,进而影响水流的水力特性。即流量相同条件下,当壁面粗糙度增大时,断面水深增大,平均流速减小,雷诺数和弗汝德数均减小。并根据试验资料拟合出了糙率系数和等效粗糙度之间的关系式。     

多弯段溢洪道加设导流墩糙条后水流三维数值模拟

"635"水库为多弯段溢洪道 ,为了充分体现加设导流墩糙条等辅助消能导流措施对多弯段溢洪道水流的影响 ,通过标准 k- ε模型和VOF多相流方法并建立三维数学模型 ,得到了溢洪道各典型断面流速大小以及水深的分布规律.数值模拟结果与模型试验结果对比表明 ,使用的数值模型能较精确地模拟加设辅助措施后溢洪道的水流流态.结果表明溢洪道水流由于受导流墩糙条等辅助消能导流措施的影响 ,能有效控制弯道环流的发生以及缩短纵向流速分布调整的距离.从而为多弯段溢洪道的水力设计提供可靠的理论依据.     

Robust Parameter Set Selection for a Hydrodynamic Model Based on Multi-Site Calibration Using Multi-Objective Optimization and Minimax Regret Approach

A robust parameter set (ROPS) selection method for a hydrodynamic flow model was proposed based on the multi-site calibration by combining multi-objective optimization with the minimax regret approach (MRA). The multi-site calibration was defined by a multi-objective optimization problem for which individual objective functions were used to measure errors at each site. In the hydrodynamic model, coefficients of power functions that show the changing relationships between Manning’s roughness and discharge in each sub-reach were optimized by minimizing the residuals of multiple sites. Different combinations of weights were assigned to sites in the application of an aggregation approach to solve the multi-objective function, and the corresponding Pareto optimal parameter sets were assumed as the ROPS candidates. All performance measures to individual Pareto optimal parameter sets were calculated and the ROPS was determined using MRA. The set which has the lowest maximum regret obtained by averaging the results from calibration and validation was determined as the only ROPS. It was found that the estimated variable roughness and the corresponding computed water levels varied considerably depending on the weights assigned to sites. Using the proposed method, the task to assign proper weights on multiple sites can be easily achieved for multi-site calibration problems. This study provides a multi-criteria decision making method to choose a ROPS that has the lowest potential regret among various alternatives for hydrologic and hydraulic models.     

渠道糙率率定误差分析

本文研究了渠道糙率率定误差与水力测量误差的函数关系。根据水力学原理,提出了计算渠道糙率率定误差的公式,然后计算分析了南水北调中线京石段应急供水工程实测流量、水深误差产生的渠道糙率率定的误差.得到重要结论:(1)微小的水力测量误差可能产生较大的渠道糙率率定误差,现有南水北调中线典型渠道原型观测糙率误差可达11%;(2)糙率的流量误差分量相对值与流量测量误差基本相同;(3)糙率的进出口水深误差分量绝对值非常接近,两者绝对值大小不仅与水深测量误差成正比,而且与渠道长度有关,当渠道过短时,糙率的水深误差分量将成倍增加。