Experimental estimation of the head loss coefficient at surcharged four-way junction manholes

ABSTRACT

The head loss caused by the surcharged flow from four-way junction manholes is the main cause of increased flood damage in urban areas. The flow pattern significantly varies depending on the inflow conditions of the inlet pipes and constitutes the flow conditions of a four-way junction manhole, three-way junction manholes, and middle manholes. Therefore, the head loss changes with various manhole shapes must be analyzed. In this study, physical model study apparatus was prepared. Various flow rate conditions were selected by changing the flow rate ratios of the inlet pipes at 10% intervals. The head loss coefficients were also estimated. A head loss coefficient range diagram was generated based on the results. A head loss coefficient empirical formula that considers all flow conditions for surcharged four-way junction manholes is proposed. The proposed equation should be applicable to the design and assessment of drainage systems with varying inlet pipe flow rates.     

Validation of 2D shock capturing flood models around a surcharging manhole

This work offers a detailed validation of finite volume (FV) flood models in the case where horizontal floodplain flow is affected by sewer surcharge flow via a manhole. The FV numerical solution of the 2D shallow water equations is considered based on two approximate Riemann solvers, HLLC and Roe, on both quadrilateral structured and triangular unstructured mesh-types. The models are validated against a high resolution experimental data-set obtained using a physical model of a sewer system linked to a floodplain via a manhole. It was verified that the sensitivity of the models is inversely proportional to the surcharged flow/surface inflow ratio, and therefore requires more calibration from the user especially when concerned with localised modelling of sewer-to-floodplain flow. Our findings provide novel evidence that shock capturing FV-based flood models are applicable to simulate localised sewer-to-floodplain flow interaction.     

Impacts of climate change on urban drainage systems – a case study in Fredrikstad,Norway

Norway has frequently encountered flood damage in urban areas during recent years. In this paper the authors, taking Veumdalen catchment in Fredrikstad as an example, simulated the possible consequences in the sewer system, in the present, predicted and artificial climate scenarios. Indicators that describe (1) surface flooding, (2) surcharging sewers, (3) basement flooding and (4) combined sewer overflow (CSO) are defined to represent the adverse effects of climate change. It is concluded from the annual-based simulation that the total volume of water spilling from the flooding manholes will increase 2–4-times the increase in precipitation, and the total CSO will increase 1.5–3-times as much as the increase in precipitation. The simulation results also show that the number of flooding manholes and number of surcharging sewers may change dramatically and irregularly with a slight change of precipitation, and vary with events and durations.     

Modelling sewer discharge via displacement of manhole covers during flood events using 1D/2D SIPSON/P-DWave dual drainage simulations

In urban areas, overloaded sewers may result in surcharge that causes surface flooding. The overflow from sewer systems mainly starts at the inlets until the pressure head in the manhole is high enough to lift up its cover, at which stage the surcharged flow may be discharged via the gap between the bottom of the manhole cover and the ground surface. In this paper, we propose a new approach to simulate such a dynamic between the sewer and the surface flow in coupled surface and sewer flow modelling. Two case studies are employed to demonstrate the differences between the new linking model and the traditional model that simplifies the process. The results show that the new approach is capable of describing the physical phenomena when manhole covers restrict the drainage flow from the surface to the sewer network and reduce the surcharge flow and vice versa.     

Optimal design of stepped spillways using the HBMO algorithm

Studies on stepped spillways as flood energy dissipators have been conducted to understand the hydraulics on the stepped face of roller-compacted concrete dams as well as overlays of embankment dams. Significant energy losses occur along the stepped chute so that the energy dissipation structure becomes smaller and more economic. In addition, considering the design discharge, downstream face slope, height of spillway, different combinations of spillway width and number of spillway steps may lead to different head losses. In each feasible combination, the remaining head after the steps should be dissipated by downstream energy dissipators. Design and construction of spillways and energy disspators are very cost-consuming and build up a major part of the dam's construction expenses. Thus, the cost of a financially viable stepped spillway project that consists of the steps’ cost and downstream dissipator's cost should be minimised. In this paper, the honey-bee mating optimisation (HBMO) algorithm is used to determine the best combination of design variables so as to minimise the total cost of both spillway chute and stilling basin. Results are compared with those previously obtained by genetic algorithm (GA) and show the promising potential of the HBMO algorithm in this field of application.     

城市雨洪控制利用的雨水径流系数分析

近二三十年来,发达国家在城市雨洪控制利用领域有了巨大发展,产生了很多新的理论、方法和技术,也改变了传统的城市雨水系统的很多设计理念和方法.径流系数是雨洪控制利用理论分析和工程设计常用的参数,但径流系数有不同的含义,它们的统计计算方法、适用条件、应用目的和取值都会不同.国内文献对径流系数的理解和表述一直比较片面简单,多数参考资料中也没有对其应用条件进行明确区分和合理表述,使得实际应用中存在概念混淆和使用困惑的问题,随着新型雨洪控制利用理念与不同功能技术的推广应用,这个问题愈显突出.对不同径流系数及其影响因素进行了梳理和总结分析,对雨量径流系数(场次雨量径流系数、年均雨量径流系数)和流量径流系数(瞬时流量径流系数、峰流量径流系数)的理论与应用作了简要介绍,为科学地进行城市雨洪控制利用系统的理论研究、规划设计和工程应用提供参考.     

The Design of Urban Road Manhole Covers Based on the Function of Safety and Identification

This study combed the development process of urban road manhole cover at home and abroad,and pointed out the existing problems in the domestic manhole cover.From the perspective of safety and identification function,it put forward innovative design ideas of urban road manhole covers to improve the safety and identification function of road manhole covers,and enhance the ornamental of manhole covers.     

Citywide multi-grid urban flood modelling: the July 2012 flood in Beijing

Global flood management is a major issue for most cities which have to deal with worsening factors such as climate change and fast urban growth. Computer models have been used to model and understand urban flooding on a local scale in cities (25–50 km²). It has been practically impossible to model bigger cities in one go in sufficiently high resolution due to the heavy computations involved.

The present paper describes a new modelling approach for urban flooding which allows modelling on large city scale (1000 km²) while keeping sufficient resolution, e.g. 5 m or 10 m grid. The multicell approach is applied for the city of Beijing for July 21st, 2012 flood event. Model results are compared to testimonials from the 2012 event. Comparison to traditional 2D urban flood computations shows that the multicell approach is much faster than standard detailed models while keeping a suitable level of precision.     

Design hydrograph and routing scheme for flood mapping in a dense urban area

Definition of flood risk maps is a task to which modern surface hydrology devotes substantial research effort. Their impact on the management of flood-prone, dense, urban areas has increased the need for better investigation of inundation dynamics. The problems associated with the aforementioned topics range from the definition of the design hydrograph and the identification of the surface boundary conditions for the flood routing over the inundation plan, to the choice of the hydrodynamic model to simulate urban flooding. Most of academic and commercial mathematical models, solving the De Saint Venant equations, fail on complex topography. Frequently encountered difficulties concern steep slopes, geometric discontinuities, mixed flow regimes, and initially dry areas. In the present paper, flood routing modelling approaches in urban areas and principles for the definition of the design flood events are outlined. The paper shows how urban flooding can be simulated by a quasi-2D hydrodynamic model that makes use of a network of connected channels and storages to simulate flow, respectively, on the streets and into the building blocks. Furthermore, the paper shows that, when flood hazard is assessed by considering flood extent, water depth and flow velocity, an in-depth analysis of the use of design hydrographs that maximise peak flow or inundation volume is needed.     

浅析检查井在城市道路中的病害

总结出城市道路检查井存在的问题,从五方面分析了检查井井盖周围病害原因,针对四种病害探讨了具体的解决办法,从而减少城市主干道检查井周围病害,保证道路的完整性和稳定性。     

Energy consumption and urban texture

This paper explores the effects of urban texture on building energy consumption. It is based on the analysis of digital elevation models (DEMs)—raster models of cities which have proven to be very effective in the urban context. Different algorithms are proposed and discussed, including the calculation of the urban surface-to-volume ratio and the identification of all building areas that are within 6 m from a façade (passive areas). An established computer model to calculate energy consumption in buildings, the LT model, is coupled with the analysis of DEMs, providing energy simulations over extensive urban areas. Results for the three case study cities of London, Toulouse and Berlin are presented and discussed.     

Computational intelligence methods for the efficient reliability analysis of complex flood defence structures

With the continual rise of sea levels and deterioration of flood defence structures over time, it is no longer appropriate to define a design level of flood protection, but rather, it is necessary to estimate the reliability of flood defences under varying and uncertain conditions. For complex geotechnical failure mechanisms, it is often necessary to employ computationally expensive finite element methods to analyse defence and soil behaviours; however, methods available for structural reliability analysis are generally not suitable for direct application to such models where the limit state function is only defined implicitly. In this study, an artificial neural network is used as a response surface function to efficiently emulate the complex finite element model within a Monte Carlo simulation. To ensure the successful and robust implementation of this approach, a genetic algorithm adaptive sampling method is designed and applied to focus sampling of the implicit limit state function towards the limit state region in which the accuracy of the estimated response is of the greatest importance to the estimated structural reliability. The accuracy and gains in computational efficiency obtainable using the proposed method are demonstrated when applied to the 17th Street Canal flood wall which catastrophically failed when Hurricane Katrina hit New Orleans in 2005.     

Optimization of the restructuring cost of an urban drainage network

Urban drainage networks are subjected to increased runoff caused by urbanization and climate change. Wear and tear, coupled with a lack of network maintenance, reduces the hydraulic capacity of these networks and results in surcharged flows, discharges and overflows calling for the need to institute effective restructuring strategies. The purpose of this study was to develop an optimization model for the optimal selection and placement of structural best management practices (BMPs). In this research, four types of structural BMPs were being considered (i.e., retention pond, green roofs, infiltration trenches and vegetated depressions). The objective function was to minimize the total cost of BMPs, within the constraints of (1) draining infrequent heavy rainfall without surcharging the conduits and (2) driving frequent small rainfall into the water-treatment plant without overflows. The model was tested on a case study in the Greater Montreal Area and the results obtained from the model effectively demonstrated its capacity to improve the hydraulic and environmental performances by adopting optimal BMPs placement strategies.     

Centrifuge Modeling on Manhole Uplift in a Liquefied Trench

The uplift behavior of sewage manholes due to liquefaction in a trench is investigated through a series of dynamic centrifuge model tests. The objectives of a series of tests are to study the mechanism of the uplift and to obtain relationships among uplift displacement and factors affecting the uplift. The factors considered in the experiments are the ground water levels, the magnitude of input accelerations, the duration time of shaking, the relative densities of trench backfill and the native ground, the material of native ground, the volume of a trench, the apparent unit weight of a manhole, and the contact conditions at the bottom of a manhole. Test results show that the primary cause of uplift is the reduction of the effective confining stress near the bottom of a manhole due to strong shaking. The magnitude of uplift is found to be strongly correlated with the ground water depth, the intensity of shaking, the shear deformation of the trench, and the contact conditions at the bottom of the manhole. These findings are believed to be useful for engineering practice in the mitigation of the manhole uplift.     

Spatial and temporal analysis of urban flood risk assessment

Urban flood risk assessment requires quantification of uncertainty that is spatially and temporally variable. This paper presents a new approach to urban flood risk assessment by: (a) integrating objective and subjective uncertainties and (b) providing full insight into spatial and temporal change of flood risk. A 1-D storm sewer model and a 2-D surface flow model are integrated to describe the dynamic interactions between overland flow on the streets and flow through the storm sewer network. The fuzzy set theory approach is used to assess spatial and temporal variability of urban flood damage, and the acceptable level of partial flood damage. The spatial and temporal variability of fuzzy performance indices: (i) combined reliability-vulnerability; (ii) robustness and (iii) resiliency, are generated as the outcome of the urban flood risk analysis. The methodology is illustrated using the residential community of Cedar Hollow (London, Ontario, Canada) as a case study.     

基于地理信息系统的城市建筑能耗模型建立方法

为降低城市快速膨胀导致的能源消耗及温室气体总量,城市环境建筑能耗分析已经成为研究热点,但是城市环境中区域建筑能耗模型尚处于初步研究阶段。随着我国城市地理信息系统及相关数据库的完善,为建立准确且预测功能完善的建筑能耗模型提供了便利条件。重点探讨根据城市地理信息系统及相关统计数据,建立三维城市环境建筑动态能耗模型。重点分析了可能遇到的主要问题及解决方法,包括如何简化地理信息系统的数据、考虑城市建筑复杂性、模型建立的自动化完成、全局敏感性分析节能措施等。并且用2个实例说明处理空间规模不同的建筑群可采用的不同建模方法。研究不仅为城市节能提供指导,也为建筑信息模型的发展和促进城市规划领域中建筑能耗模型的广泛应用提供了坚实基础。     

同程与异程采暖系统在节能方面的比较

利用对比沿程水头损失及局部水头损失的方法,分析了同程系统和异程系统的总体能耗,得到同程系统的能耗小于异程系统的结论,并进一步推广同程系统的使用,以达到节能的目的。     

Effectiveness of predicting tunneling-induced ground settlements using machine learning methods with small datasets

Prediction of tunneling-induced ground settlements is an essential task, particularly for tunneling in urban settings. Ground settlements should be limited within a tolerable threshold to avoid damages to aboveground structures. Machine learning(ML) methods are becoming popular in many fields, including tunneling and underground excavations, as a powerful learning and predicting technique. However, the available datasets collected from a tunneling project are usually small from the perspective o...     

Laboratory Investigation into the Performance of an In-Sewer Vortex Flow Regulator

Aspects of the hydraulic performance of an in-sewer vortex regulator have been studied. These devices are increasingly used in stormwater management schemes, but their characteristics under a variety of prototypical situations have not been widely disseminated. The study used a full-size laboratory mockup of a section of sewer and associated manhole with facilities for measuring discharges of up to 60 1/s. The performance of a typical vortex flow regulator was investigated under both steady and unsteady flow conditions. The steady head-discharge relationship revealed the expected 'kick back'region (during rising head); however, this was less pronounced during falling head. Under unsteady conditions, vortex initiation was affected and a hysteresis effect was noted. The influence of downstream surcharge was significant at lower upstream heads. Theoretical comparison showed that to obtain equivalent performance, an orifice of 62% of the diameter of the vortex regulator would be required, and 25% savings in storage could be made.     

A new clustering and visualization method to evaluate urban heat energy planning scenarios

Spatial visualization is a very useful tool to help decision-makers in the urban planning process, i) to define future energy transition pathways, ii) to implement energy efficiency strategies and iii) to integrate renewable energy technologies in the context of sustainable cities. There is thus a need to develop new tools to understand the energy consumption patterns across cities. Statistical methods are often used to understand the driving parameters of energy consumption but rarely used to evaluate future urban refurbishment scenarios. Simulating whole cities using energy demand softwares can be very extensive in terms of computer resources and data collection. A new methodology, using city archetypes, is hence proposed to simulate the energy consumption of urban areas and to evaluate urban energy planning scenarios. The objective of this paper is to present a solid framework and innovative solution for the computation and visualization of energy saving at the city scale. The energy demand of cities, as well as the microclimatic conditions, are calculated by using a 3D model designed as function of the real city urban geometrical and physical characteristics. Data are extracted from a GIS database. We demonstrate how the number of buildings to be simulated can be drastically reduced thereby significantly decreasing the computational time and without compromising the accuracy of the results. This model is then used to evaluate the influence of two sets of refurbishment solutions. The energy consumption are then integrated back in the GIS to identify the areas in the city where refurbishment works are needed more rapidly. The city of Settimo Torinese (Italy) is used as a demonstrator for the proposed methodology, which can be applied to medium-sized cities worldwide with limited amount of information.