Research of the performance of pulse electrohydrodynamics in blockage removal

In line with contemporary trends and seeking to develop new methods and technologies, a new, original technology was explored and designed based on a non-conventional process of electrical pulse discharge in a water chamber, referred to as 'Pulse Electrohydrodynamic Technology' (PELHYDT). The application of the PELHYDT in sewer blockage removal is presented in this paper. Existing machinery can remove two blockages of gully pot connections per hour. Three blockages of pipe conduits are generally removed during an 8-h working day. Applying PELHYDT technology, which allows for high rates of removal of mechanical obstructions, it is possible to achieve operating fluid pressures in the order of 10(3)-10(4) bars, a velocity of 100 m/s, a deformation acceleration of the model material structure of 10(6)-10(7) m/s2, and high-frequency hydraulic shock waves with a frequency of 10(3)-10(4) Hz. The applicability of this efficient technology in sewer blockage removal was proven under laboratory conditions at operating fluid pressures from 50 to 160 bars, which are standard for sewer maintenance. Water velocities generally achieved in sewers using existing flushing technologies range between 1 and 3 m/s and usually do not exceed 9 m/s. PELHYDT creates waves whose velocity is at least 100 m/s, and is therefore about ten times more efficient than existing technologies. PELHYDT generates an electrohydrodynamic wave very quickly, virtually in the form of an explosion. It was proven under laboratory conditions that the application of this technology for blockage removal in practice will not result in any sewer damage.     

Urban flood risk assessment using sewer flooding databases

Sustainable water management is a global challenge for the 21st century. One key aspect remains protection against urban flooding. The main objective is to ensure or maintain an adequate level of service for all inhabitants. However, level of service is still difficult to assess and the high-risk locations difficult to identify. In this article, we propose a methodology, which (i) allows water managers to measure the service provided by the urban drainage system with regard to protection against urban flooding; and (ii) helps stakeholders to determine effective strategies for improving the service provided. One key aspect of this work is to use a database of sewer flood event records to assess flood risk. Our methodology helps urban water managers to assess the risk of sewer flooding; this approach does not seek to predict flooding but rather to inform decision makers on the current level of risk and on actions which need to be taken to reduce the risk. This work is based on a comprehensive definition of risk, including territorial vulnerability and perceptions of urban water stakeholders. This paper presents the results and the methodological contributions from implementing the methodology on two case studies: the cities of Lyon and Mulhouse.     

The role of settling velocity formulation in the determination of gully pot trapping efficiency: comparison between analytical and experimental data

Roadside gully pots are the connecting points between surface runoff and the underground drainage network; therefore they can be considered as the most superficial component of urban drainage systems. Gully pots are supposed to trap particulate matter washed off the catchment surface, but also to collect and convey stormwater into the network. The continuous accumulation of particulate matter results in a progressive loss of the gully pot hydraulic conveyance, thereby increasing the probability of urban flooding during rainstorm events. This study has therefore the objective to determine which variables influence the gully pot capability of retaining solids (efficiency), both experimentally and analytically. Several laboratory tests have been performed on a simple plastic gully pot, with different inflow rates and using both mono and hetero-disperse particle samples. Particular attention has been given to the influence exerted by the way particle settling velocity is expressed: efficiency has been analytically determined by means of multiple settling velocity formulas proposed by various authors and eventually compared to experimental data. Results deriving from the adoption of each single settling velocity formula have been extensively analysed, showing fairly different outcomes.     

Estimation of uncertainty in long term combined sewer sediment behaviour predictions, a UK case study.

There are regulatory driven requirements for UK water companies to reduce the number of properties at risk of sewer flooding. One of the potential causes of sewer flooding is the presence of persistent sediment deposits in sewers. This is a common problem in many combined sewers. Although the regulation is risk based, there is a gap in current knowledge on how risk assessment is affected by the uncertainty in sewer solids behaviour prediction. This paper describes a UK case study exploring the possibility of estimating uncertainty in sewer sediment deposit level predictions, using Monte Carlo simulations combined with a response database.     

Decision making in flood risk based storm sewer network design

It is widely recognised that flood risk needs to be taken into account when designing a storm sewer network. Flood risk is generally a combination of flood consequences and flood probabilities. This paper aims to explore the decision making in flood risk based storm sewer network design. A multiobjective optimization is proposed to find the Pareto front of optimal designs in terms of low construction cost and low flood risk. The decision making process then follows this multi-objective optimization to select a best design from the Pareto front. The traditional way of designing a storm sewer system based on a predefined design storm is used as one of the decision making criteria. Additionally, three commonly used risk based criteria, i.e., the expected flood risk based criterion, the Hurwicz criterion and the stochastic dominance based criterion, are investigated and applied in this paper. Different decisions are made according to different criteria as a result of different concerns represented by the criteria. The proposed procedure is applied to a simple storm sewer network design to demonstrate its effectiveness and the different criteria are compared.     

Development and Comparison of Two Fast Surrogate Models for Urban Pluvial Flood Simulations

Detailed full hydrodynamic 1D-2D dual drainage models are a well-established approach to simulate urban pluvial floods. However, despite modelling advances and increasing computational power, this approach remains unsuitable for many real time applications. We propose and test two computationally efficient surrogate models. The first approach links a detailed 1D sewer model to a GIS-based overland flood network. For the second approach, we developed a conceptual sewer and flood model using data-driven and physically based structures, and coupled the model to pre-simulated flood maps. The city of Ghent (Belgium) is used as a test case. Both surrogate models can provide comparable results to the original model in terms of peak surface flood volumes and maximum flood extent and depth maps, with a significant reduction in computing time.     

Local head loss monitoring using acoustic instrumentation in partially full sewer pipes

After an increase in capital investment in UK sewers to reduce hydraulic capacity problems, the proportion of sewer flooding incidents now linked to blockages has increased. It is clear that if sewer operators are to continue to reduce flooding incidents, then better blockage management is now required. Sewer blockage formation is poorly understood; blockages are intermittent and occur in a number of circumstances. This paper reports on the development of low-cost acoustic instrumentation that can identify the location of a pipe blockage and then estimate the local head loss as a result of the presence of a blockage. A set of experiments were carried out in two full-scale laboratory pipes. The pipes' condition was altered by inserting blockages of different sizes. Acoustic data were recorded and presented in terms of the acoustic energy reflected from the partially blocked pipe. The results of this study show that the total reflected acoustic energy correlates with the measured head loss. A new empirical relation between the reflected acoustic energy and head loss due to a blockage is derived. This knowledge can then be used to estimate the reduction in flow capacity resulting from a blockage based on a single remote measurement.     

Multi-criteria Approach for Selection of Green and Grey Infrastructure to Reduce Flood Risk and Increase CO-benefits

Continuous changes in climate conditions combined with urban population growth pose cities as one of the most vulnerable areas to increasing flood risk. In such an atmosphere of growing uncertainty, a more effective flood risk management is becoming crucial. Nevertheless, decision-making and selection of adequate systems is a difficult task due to complex interactions between natural, social and built environments. The combination of green (or sustainable) and grey (or traditional) options has been proposed as a way forward to ensure resilience in advance of extreme events, and at the same time to obtain co-benefits for society and the environment. The present paper describes a novel method for selection of urban flood measures, based on a multi-criteria analysis that includes flood risk reduction, cost minimization and enhancement of co-benefits. The aim of this method is to assist decision makers in selecting and planning measures, which afterwards can be part of either high level scoping analysis or more complex studies, such as model based assessment. The proposed method is implemented within a tool which operates as a standalone application. Through this tool, the method has been applied in three study cases. The findings obtained indicate promising potential of the method here introduced.     

基于复杂网络方法的既有雨水管段脆弱性判定

为减轻城市暴雨造成的洪涝灾害,找出影响既有雨水管段脆弱性的薄弱环节,介绍了城市雨水管网系统脆弱性及雨水管段脆弱性的概念,总结了既有雨水管段脆弱性所涉及的影响因素,综合分析了各功能模块之间的相关程度,并且在此基础上结合复杂网络拓扑模型,提出了一种利用节点的重要度来确定既有雨水管段脆弱性判定的方法。结果表明,该方法能够体现节点之间的重要性差异,使节点脆弱性的判定更加准确,为后续进行城市雨水管网改造、修建提供理论依据,为将来建设海绵城市建设重要分支之一的智慧排水管网系统提供事故管段预警,提高事故抢修和维修服务的效率。     

基流分割对城市雨洪模拟不确定性分析的影响

为了探究基流分割对城市雨洪模拟的影响,以济南市主城区流域为例构建SWMM模型,采用2005—2010年7场基流分割前后的实测洪水资料校验模型,应用GLUE方法,以均方根误差为似然评判依据对模拟结果进行不确定性分析,探讨了基流分割前后流量数据对模拟结果不确定性的影响。结果表明：各场次暴雨基流占洪峰流量的比例均值为13.38%,对洪水模拟效果影响较大;GLUE方法能够有效提取高精度参数集,相比于原始流量序列,应用基流分割后流量作为校验模型依据,流量过程90%置信区间覆盖率增大100%,平均偏移幅度和平均对称度分别减小42.60%和87.19%。通过基流分割可有效降低流量数据作为模型校验数据导致的模拟结果不确定性,提升洪水预报性能,获取更精确对称的流量预报区间。     

苏锡常排涝对江南运河产生的洪涝转移特征

基于丰富翔实的基础资料,建立了专门的水文水动力模型,分析现状调度方案、优化调度方案及不设防方案下苏锡常城市排涝对江南运河水位的影响,并分析城市内部洪涝特征及区域洪涝转移规律。结果表明:与不设防方案对比,现状调度方案能降低常州、无锡、苏州的城市洪峰水位0.28～1.10 m,说明城区大包围有效地降低了城区洪水风险,保证了城区安全,但江南运河的水位随降水量和苏锡常城市排涝量的增加而增大。若采用优化调度方案,城市起排水位适当抬高0.17～0.30 m,运河水位会降低0.00～0.12 m,说明在不大幅增加城市洪涝风险的基础上,可以适当减少城市的排涝量,从而降低江南运河水位,协调城市与区域的防洪关系。     

多源城市暴雨预报数据融合研究进展

全球气候变化和快速城市化改变了城市水循环过程,加剧了城市暴雨洪涝问题。为有效预报洪水,减轻洪涝灾害,借助水文水力模型对城市水循环的各个环节进行模拟。而单一暴雨预报数据的不确定性是使用水文水力模型模拟预报洪水面临的重大挑战。从城市雨洪模型输入不确定性的角度出发,回顾了暴雨预报技术的发展历程,总结了各种预报方法的特点、适用性和局限性,指出基于单一暴雨预报数据驱动模型预报洪水的不足,提出多源暴雨预报数据融合的基本框架。未来应强化降雨观测和定量降水预报能力,发展多源信息耦合技术,实现高精度、长预见期的洪水预报,为城市防洪减灾提供依据。     

Application of a leakage model to assess exfiltration from sewers.

The exfiltration of wastewater from sewer systems in urban areas causes a deterioration of soil and possibly groundwater quality. Beside the simulation of transport and degradation processes in the unsaturated zone and in the aquifer the analysis of the potential impact requires the estimation of quantity and temporal variation of wastewater exfiltration. Exfiltration can be assessed by the application of a leakage model. The hydrological approach was originally developed to simulate the interactions between the groundwater and surface water, it was adapted to allow for modelling of interactions between groundwater and sewer system. In order to approximate the exfiltration specific model parameters infiltration specific parameters were used as a basis. Scenario analysis of the exfiltration in the City of Dresden from 1997 to 1999 and during the flood event in August 2002 shows the variation and the extent of exfiltration rates.     

Rehabilitation of Urban Drainage Systems Using a Resilience-Based Approach

Highly efficient methods are needed to mitigate negative impacts of urban storms such as flooded roads and damage to properties and infrastructures. A rehabilitation approach based on resiliency is proposed in this paper for urban drainage systems using structural improvement of bottlenecks. The resilience-based approach enhances system capability to act very flexible against exceptional loads such as bridge/culvert blockage during the floods. The approach integrates a multi-objective evolutionary algorithm (MOEA) and EPA-SWMM simulation model to find cost-effective rehabilitation measures under structural failure of critical elements in the network. It is applied to the western part of Tehran Stormwater Drainage System (TSDS) to attain optimal measures by minimizing the costs and flood volumes. The approach outperforms the conventional methods (particularly compared to a previous rehabilitation proposal for the study area) when the system encounters unexpected blockage conditions. Results show that the optimal design obtained by the proposed approach can decrease network flooding from 3.5 × 10⁶ m³ to near zero with at most 23% lower investment costs relative to the traditional design.     

Characterization of runoff from various urban catchments at different spatial scales in Beijing, China

In order to investigate the characterization of runoff in storm sewer from various urban catchments, three monitoring systems at different spatial scales have been installed separately. They have been held since July 2010 in urban area of Beijing (China). The monitoring data revealed that chemical oxygen demand (COD), total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP), and NH(3)-N values significantly exceed the Class V surface water quality standard developed by Ministry of Environmental Protection of the People's Republic of China (MEP). A surface solids buildup and wash off model for small watershed was adopted to analyze and discuss the process of a runoff pollutant discharge. More than a half of pollutant parameters presented a good fit to the model. However, a slightly worse-fit to the wash off model appeared in less than half of the data. Due to the influence of sewer sediments, sewer system characteristics, catchment characteristics, and other reasons, first flush was seldom observed in storm sewer runoff from these three survey areas. Meanwhile, the correlation between TSS and any other pollutant was analyzed according to cumulative load of pollutants in runoff events. An event mean concentrations (EMCs) approach was adopted to quantify the pollution of runoff. EMCs of various pollutants in storm sewer runoff between different rainfall events were slightly higher than the typical values observed in similar areas at home and abroad, according to other studies reported in literature. Based on quantitative analysis, it can be concluded that urban non-point source pollution is recognized as the major causes of quality deterioration in the receiving water bodies. This is after the point source pollution has been controlled substantially in Beijing. An integrated strategy, which combines centralized and decentralized control, along with the conditions of meteorology, hydrology, urban planning, existing drainage system, etc., will be an effective and economic approach to urban runoff pollution control.     

Inundation analysis of the effectiveness of an estuarygate in Hori River

Storm surges and floods around bays in Japan frequently result in water disasters. Both dikes and estuary gates can be constructed in urban areas near bays as counter measures. Estuary gates at the mouth of a river are intended to protect the upstream areas from storm surges and tsunamis. The sewer systems in urban areas also decrease the inundation. In this study, a numerical simulation is carried out to examine the effectiveness of the estuary gate and performance of the sewer system. A synthetic analysis model of inundation phenomena is developed and applied to the behavior of water in the urban area near the Nagoya Port and the estuary region of the Hori River. The developed model consists of models for the sea, river, sewer, overland flood flow, and typhoon. The inundation analysis model is validated by a comparison of analytical and observed results. The features of the inundations in the urban area caused by various conditions are discussed.     

Inundation analysis of the effectiveness of an estuarygate in Hori River

Storm surges and floods around bays in Japan frequently result in water disasters. Both dikes and estuary gates can be constructed in urban areas near bays as counter measures. Estuary gates at the mouth of a river are intended to protect the upstream areas from storm surges and tsunamis. The sewer systems in urban areas also decrease the inundation. In this study, a numerical simulation is carried out to examine the effectiveness of the estuary gate and performance of the sewer system. A synthetic analysis model of inundation phenomena is developed and applied to the behavior of water in the urban area near the Nagoya Port and the estuary region of the Hori River. The developed model consists of models for the sea, river, sewer, overland flood flow, and typhoon. The inundation analysis model is validated by a comparison of analytical and observed results. The features of the inundations in the urban area caused by various conditions are discussed.     

Improving Urban Drainage Systems Resiliency Against Unexpected Blockages: A Probabilistic Approach

Considering the increase of flood hazards in many large cities, the rehabilitation of hydro-urban infrastructures is an important concern for the municipal authorities. A probabilistic approach based on Monte Carlo Simulation (MCS) is presented in this study to improve the resiliency of urban drainage systems when they are subject to unexpected structural blockages. The approach is integrated with SWMM simulation model and an evolutionary search algorithm to find the best set of rehabilitation measures under a significant number of blockage scenarios. Experimental results on the west zone of main drainage system in Tehran city indicate that proposed approach outperforms the conventional hydraulic-based methodology in terms of cost effectiveness and functionality. Results also show that adding the redundancy to the system by bypass lines in bottlenecks is considerably more efficient for flood mitigation and the increase of system resiliency under blockage incidents rather than using conventional methods such as detention ponds and enlargement of the channel sizes.     

Assessment of data and parameter uncertainties in integrated water-quality model

In integrated urban drainage water quality models, due to the fact that integrated approaches are basically a cascade of sub-models (simulating sewer system, wastewater treatment plant and receiving water body), uncertainty produced in one sub-model propagates to the following ones depending on the model structure, the estimation of parameters and the availability and uncertainty of measurements in the different parts of the system. Uncertainty basically propagates throughout a chain of models in which simulation output from upstream models is transferred to the downstream ones as input. The overall uncertainty can differ from the simple sum of uncertainties generated in each sub-model, depending on well-known uncertainty accumulation problems. The present paper aims to study the uncertainty propagation throughout an integrated urban water-quality model. At this scope, a parsimonious bespoke integrated model has been used allowing analysis of the combinative effect between different sub-models. Particularly, the data and parameter uncertainty have been assessed and compared by means of the variance decomposition concept. The integrated model and the methodology for the uncertainty decomposition have been applied to a complex integrated catchment: the Nocella basin (Italy). The results show that uncertainty contribution due to the model structure is higher with respect to the other sources of uncertainty.     

Water quality-based assessment of urban drainage impacts in Europe - where do we stand today?

Traditionally, design and optimisation of urban drainage systems was mainly driven by cost efficiency, surface flood prevention, and later by emission reduction. More recent procedures explicitly include ecological conditions of the receiving water in the definition of acceptable pollutant discharges via sewer system and treatment plant outlets. An ambient Water Quality based impact Assessment (WQA) principle therefore requires an integrative system optimisation. However, a broad range of mostly national WQA protocols exist across Europe varying in structure and complexity, assessment concept, spatial and temporal scope and handling of uncertainty. This variety inherently implies a considerable risk of subjectivity in the impact assessment with highly variable outcomes. The present review identifies differences and similarities of WQA protocols in use and discusses their strengths and weaknesses through: (i) a systematic comparison of WQA protocols by selected attributes, (ii) a review of real-life cases reported in the literature and expert interviews, and (iii) an illustration of our main findings by applying selected WQA in an instructive example. The review discusses differences in structure and concept, which are mainly identified for simplistic WQA protocols. The application of selected protocols to an example case shows a wide variety of numerical results and conclusive decisions. It is found that existing protocols target different questions within the decision making process, which users should be more aware of. Generally, to make assessments more reliable, further fundamental research is required to fully understand the relationship between stressors and stream ecosystem responses which will make assessments more reliable. Technically, tools suggested in WQA protocols show severe deficiencies and an uncertainty assessment should be mandatory.