Performance Of Urban Drainage Systems Research Articles

Development of a risk-based optimization approach to improve the performance of urban drainage systems

ABSTRACT Considering the great deal of rainfall uncertainty in urban drainage system (UDS) design/rehabilitation, a copula-based design approach is developed within a Monte Carlo simulation (MCS) to improve system performance. Firstly, inundation zones are determined using HEC-RAS 2D and GIS tools. Then, inundation zones of flood scenarios are integrated with damage–depth functions in GIS to obtain the associated damage costs. Accordingly, a mapping is made between the flood volume (calculated by EPA-SWMM) and its related damage. This information is used in a coupled EPA-SWMM and differential evolution (DE) search algorithm to determine the best rehabilitation strategies. The approach is applied to a catchment in Tehran and its results are compared with the return-period method. Results show that the risk-based design approach could provide a 92% reduction in expected annual flood damage (EAD) and presents optimal designs with benefit-to-cost ratios up to 11, according to budget level. This approach yields more robust designs/strategies relative to the return-period method.

Impacts of Climate Change on Urban Extreme Rainfall and Drainage Infrastructure Performance: A Case Study in Wuhan City, China

AbstractThe design of stormwater drainage infrastructure in urban areas in China is based on the statistical stationary assumption of probability distribution of extreme rainfall, which is being increasingly challenged by climate change. However, quantitative assessment of the performance of urban drainage systems in response to climate change with the latest emission scenarios of the Coupled Model Intercomparison Project Phase 5 in China is quite limited. This study aims to investigate potential changes of extreme rainfall and their influence on drainage infrastructure in a representative urban area in Wuhan city, China. The Storm Water Management Model is established to investigate the response of drainage infrastructure to future design rainfall. It is found that the probability distribution of extreme rainfall for two historical sub‐periods (1961–1985 and 1986–2005) has changed, especially in the head and tail of the frequency curves. Furthermore, the design rainfall with return periods of 2, 3, 4 and 5 years increases more significantly than those of 10 and 20 years. Consequently, the incapability of the current drainage infrastructure in the study area is aggravated. Moreover, the results of SWMM modelling provide detailed information about the performance of current drainage infrastructure, which can provide technical support for future modifications of the current drainage infrastructure of the study area. © 2018 John Wiley & Sons, Ltd.

Spatial Data and Catchment Discretization for Assessment Coastal Urban Drainage Performance Using GIS and MIKE URBAN-SWMM

The urban drainage model requires spatial data and catchment discretization because of the complexity of system. Using integration of Geometric Information System (GIS) technology and urban storm water models, the performance of urban drainage system can be analysed.[1] Especially in coastal area, the main problem of urban drainage is overloaded capacity because of rapid urbanization and coastal floods caused by storm surges and wave action superimposed on high water levels generated during the cycle of tides. Land use change, watershed area as settlements area, clogged drainage pipe/channel, the changing of imperviousness of land cover also contributes to large volume of surface runoff. Moreover, the developments can change land cover in urban area and increasing rainfall runoff. One of the solutions for coastal urban drainage is by using polder system for flood control. The purpose of this paper is to illustrated how GIS can model the catchment discretization and MIKE URBAN-SWMM (Storm Water Management Model) can analyse water balance based on the rainfall return period of 25, 50 and 100 years. The research shows evaluation result of the polder performance including inundation depth and pump performance by linking GIS between storm water models. The case study is analysing the Pluit polder in Jakarta-Indonesia, which is connected to the Indonesia Central Bank compartment. Based on the model, this polder system can reduce flooding in Indonesia Central Bank Compartment up to 50%, however the inundation is still occurred.

Partitioning the impacts of spatial and climatological rainfall variability in urban drainage modeling

Abstract. The performance of urban drainage systems is typically examined using hydrological and hydrodynamic models where rainfall input is uniformly distributed, i.e., derived from a single or very few rain gauges. When models are fed with a single uniformly distributed rainfall realization, the response of the urban drainage system to the rainfall variability remains unexplored. The goal of this study was to understand how climate variability and spatial rainfall variability, jointly or individually considered, affect the response of a calibrated hydrodynamic urban drainage model. A stochastic spatially distributed rainfall generator (STREAP – Space-Time Realizations of Areal Precipitation) was used to simulate many realizations of rainfall for a 30-year period, accounting for both climate variability and spatial rainfall variability. The generated rainfall ensemble was used as input into a calibrated hydrodynamic model (EPA SWMM – the US EPA's Storm Water Management Model) to simulate surface runoff and channel flow in a small urban catchment in the city of Lucerne, Switzerland. The variability of peak flows in response to rainfall of different return periods was evaluated at three different locations in the urban drainage network and partitioned among its sources. The main contribution to the total flow variability was found to originate from the natural climate variability (on average over 74 %). In addition, the relative contribution of the spatial rainfall variability to the total flow variability was found to increase with longer return periods. This suggests that while the use of spatially distributed rainfall data can supply valuable information for sewer network design (typically based on rainfall with return periods from 5 to 15 years), there is a more pronounced relevance when conducting flood risk assessments for larger return periods. The results show the importance of using multiple distributed rainfall realizations in urban hydrology studies to capture the total flow variability in the response of the urban drainage systems to heavy rainfall events.

Performance assessment of separate and combined sewer systems in metropolitan areas in southern China

To assess the performance of urban drainage systems in metropolitan areas in southern China, 12 urban drainage systems, including nine separate sewer systems (SSSs) and three combined sewer systems (CSSs) were monitored from 2008 to 2012 in Shanghai and Hefei. Illicit connection rates of SSS were determined. The results indicate that serious illicit connections exist for most SSSs. Annual volume balance for two SSSs with serious illicit connection was assessed with a hydraulic model to determine the dry weather overflow volume. Although interception facilities have been implemented in SSSs, for some systems with serious illicit connections, a considerable volume of dry weather overflow still existed. Combined with monitoring of dry/wet weather flow quality, the pollutant load caused by wet/dry weather overflow was quantified. The results revealed that there was no obvious advantage of having SSSs over CSSs in terms of pollutant control. The serious pollution caused by illicit connections and insufficient management occurs in many cities in China. The performance assessment of separate and CSSs in Shanghai and Hefei provides important lessons and practical experience that can be applied to the construction and management of urban drainage system in China as well as other developing countries.

Potential and limitations of modern equipment for real time control of urban wastewater systems

Real Time Control (RTC) has become an accepted technique for improving the performance of Urban Drainage Systems (UDS) due to its flexibility and sustainability. Numerous implementations of RTC have been reported during the last decades. At the same time, guideline documents and state-of-the-art reports have been published. Whereas the general aspects and challenges of planning and installation of RTC systems are well covered, there is a lack of information about the adequate equipment for RTC of UDS. After identifying and briefly discussing the basic components of RTC systems for UDS, this paper describes the specific components in detail. This comprises the introduction of available technologies for sensors, actuators, controllers and telemetry systems in the context of RTC and the discussion of their potential and limitations. Lessons learned from the field operational experiences and future trends and challenges are identified.

Enhanced efficiency of pluvial flood risk estimation in urban areas using spatial–temporal rainfall simulations

AbstractUrban areas are concentrations of flood risk because of the density of development and because they tend to be constructed in low‐lying areas. They may be subject to flooding from rivers or the sea but are also vulnerable to the effects of intense direct rainfall, which can overwhelm urban drainage systems, and cause complex and often localised patterns of pluvial flooding. The risk from pluvial flooding is particularly difficult to assess because it is sensitive to the spatial–temporal characteristics of rainfall, local run‐off and surface flow processes, the performance of urban drainage systems, and the exact location of buildings. Sampling the variability or uncertainty in all of these processes in order to generate accurate flood risk estimates quickly becomes computationally prohibitive, especially for large urban areas. In this paper, we evaluate alternative approaches for making use of high‐resolution spatial–temporal rainfall simulations in urban flood risk analysis. Flood depths are computed with a coupled sewer and surface flood model, and flood damage is estimated using standard depth‐damage criteria. Efficient sampling of rainfall events and judicious use of response surfaces that relate rainfall event properties to flood volumes and damages are evaluated and shown to reduce the computational expense of risk analysis by more than 70%. The risk analysis methodology is successfully demonstrated for two contrasting urban locations in the UK.

Hydraulic Impacts on Urban Drainage Systems due to Changes in Rainfall Caused by Climatic Change

Changes in climate were a growing concern during the last decade and will be even greater in the coming years. When investigating the impact from changes in the climate on urban drainage systems, two challenges are (1) what type of input rainfall data to use and (2) what parameters to use to measure the impacts. The overall objective of this study is to investigate the hydraulic performance of urban drainage systems related to changes in rainfall, and through these hydraulic parameters describe the impact of climate change. Input rainfall data represent today’s climate and three future time periods (2011–2040, 2041–2070, and 2071–2100). The hydraulic parameters used were water levels in nodes (e.g., as the number of floods, and frequency and duration of floods) and pipe flow ratio. For the study area, the number of flooded nodes and the geographical distribution of floods will increase in the future, as will both the flooding frequency and the duration of floods.

Influence of rainfall estimation error and spatial variability on sewer flow prediction at a small urban scale

Legislative drivers for water quality and urban flood risk are driving a growing need to accurately determine the performance of urban drainage systems in near real time. Rainfall data are clearly a key input to urban drainage system models. Historically rain gauge data have been used, however radar rainfall data are now widely available and benefits from significantly higher spatial coverage than rain gauges in most UK urban catchments. This paper describes a detailed study based on a small (11km2) urban catchment in West Yorkshire, England. Radar and rain gauge data have been compared and used as the input to hydrodynamic sewer flow simulations, and the results of these simulations have been compared with measured flows in the sewer system. The results showed that for this size of catchment, there can be significant differences in simulated peak flows and combined sewer overflow spill volumes due to inherent uncertainties between the two rainfall estimates.

Multiobjective Evolutionary Approach to Rehabilitation of Urban Drainage Systems

Urban flooding has become a very important and growing issue around the world. In order to maintain an acceptable performance of urban drainage systems, early rehabilitation plans must be developed and implemented. The allocation of funds to support rehabilitation works should be in a certain sense “optimal” in providing value for money. However, this is a highly demanding and not easily achievable task due to the multidimensional nature of the rehabilitation process, especially taking into account conflicting interests. In this respect, multiobjective optimization using hydrodynamic urban drainage models appears to be promising and more reliable than the traditional engineering approaches. Such optimization is used in this paper to evaluate urban drainage rehabilitation scenarios contrasting investment against flood damages. A small-scale rehabilitation problem is posed and solved. The approach has demonstrated the potential use and combination of multiobjective optimization and hydrodynamic models to an...

Minimizing sediment deposition in urban drainage channels in Ghana: Channel section design approach

The phenomenon of sediment deposition leading to the silting-up of drainage channels has been a major problem in the performance of urban drainage systems. Preventive and costly maintenance measures are often employed to mitigate the problem. In the area of design, critical or self-cleansing velocity methods have been used to achieve certain levels of flushing-out of sediment load in the channels. As an alternative to the current design practices in Ghana, this study presents the channel section approach. Deposition of suspended sediment in channels takes place mainly because of velocity fluctuations in the channel. In this study, therefore, a channel section capable of maintaining a constant vertical velocity distribution is presented. The advantage of the constant velocity channel section is that it minimizes the velocity fluctuations in the channel and subsequently reduces the deposition of sediment in the channel.

Updating Rainfall IDF Relationships to Maintain Urban Drainage Design Standards

The hydrologic design standards for urban drainage systems are commonly based on the frequency of occurrence of heavy rainfall events. Observations of recent climate history indicate that the frequency of occurrence of heavy rainfall events is increasing. This increasing trend will likely continue in the future due to global warming. In this study, extending from previous analysis results for Chicago, the rainfall intensity–duration–frequency (IDF) relationships were determined to represent the climate conditions of the first and second halves of the last century. Using these IDF relationships, the impact of the observed increase in heavy rainfall events on the design and performance of urban drainage systems were quantified. This quantification demonstrated the need for updating rainfall IDF relationships to reflect changing climate conditions. In the design of new and retrofitting or replacement of old urban drainage systems, up to date IDF relationships need to be used to maintain design standards.

Investigation and numerical modelling of roof drainage systems under extreme events

In April 2003 the UK Engineering and Physical Sciences Research Council (EPSRC) and a diverse group of interested parties began funding a number of major projects looking at the impacts of climate change on the built environment, transport and utilities. One of these projects, entitled AUDACIOUS, is concerned with the impact of climate change on all aspects of urban drainage systems. The main objective of this project is to investigate key aspects of the effects of climate change on existing drainage in urban areas, and hence provide tools for drainage managers and operators to adapt to uncertain future scenarios. A major element of this work is the development of a set of numerical models to simulate the performance of urban drainage systems under the type of extreme rainfall events associated with climate change. Once developed, it is intended to utilise such models in a diagnostic design capacity, to assist in the formulation of strategies to improve the performance of new and existing urban drainage systems under different climate change scenarios. This paper details the work that has been undertaken at Heriot-Watt University as part of the AUDACIOUS project. To date, this has involved the development of a numerical model to simulate the performance of roof drainage systems (both conventional and siphonic) under extreme rainfall events. The necessary experimental work is described, and the development of the model is detailed. Comparisons between model output and laboratory data are illustrated. Finally, conclusions are drawn regarding the progress to date, and plans for the next stage of the project are outlined.

Accounting for sensor calibration, concentration heterogeneity, measurement and sampling uncertainties in monitoring urban drainage systems

Assessing the functioning and the performance of urban drainage systems on both rainfall event and yearly time scales is usually based on online measurements of flow rates and on samples of influent and effluent for some rainfall events per year. In order to draw pertinent scientific and operational conclusions from the measurement results, it is absolutely necessary to use appropriate methods and techniques in order to i) calibrate sensors and analytical methods, ii) validate raw data, iii) evaluate measurement uncertainties, iv) evaluate the number of rainfall events to sample per year in order to determine performance indicator with a given uncertainty. Based on previous work, the paper gives a synthetic review of required methods and techniques, and illustrates their application to storage and settling tanks. Experiments show that, despite controlled and careful experimental conditions, relative uncertainties are about 20% for flow rates in sewer pipes, 6-10% for volumes, 25-35% for TSS concentrations and loads, and 18-276% for TSS removal rates. In order to evaluate the annual pollutant interception efficiency of storage and settling tanks with a given uncertainty, efforts should first be devoted to decrease the sampling uncertainty by increasing the number of sampled events.

Assessing the performance of urban drainage systems: `general approach' applied to the city of Rotterdam

The Department of Public Works for the city of Rotterdam manages a complex urban drainage system. The system consists of 30 catchments, collects wastewater discharged by 30 pumping stations, to a total of five treatment plants (1.1 million equivalent population). At present control of all these pumping stations is being centralised. To assess the benefits of central control, a performance index (PI) was developed to classify the actual performance of the system under control, during dry weather conditions and during storm events. The PI is composed of deterministic and heuristic indicators that reflect the quality of the control with respect to different objectives set for the entire water system.In a case study the PI was computed for several historic events and showed encouraging results in different modes of control for both dry weather and storm conditions. From the results it can be concluded that the technology described in this paper can help to identify points that need performance improvement in the urban water system in general and in the way it is controlled specifically.