Dušan Prodanović

Overland flow and pathway analysis for modelling of urban pluvial flooding

Research on improving an overland flow model is presented for urban pluvial flooding under the dual-drainage concept where sewer flow dynamically interacts with overland flow. This occurs during heavy storms when the sewer system is surcharged. The system becomes pressurised and overland flow increases by the additional volume flowing out from the sewer. To represent the overland flow realistically, a new methodology was developed to automatically create the overland flow network which can interact with the drainage system. Use is made of high-resolution, accurate Digital Elevation Model data collected by the LiDAR technique. This approach updates the current urban drainage models to urban flood models with detailed representation of overland flow processes such as pond forming, flow through preferential surface pathways and surface drainage capacity. This work advances new areas of urban flood management including improvement in real-time control and of links with rainfall now-casting, and short term urban flood forecasting. The dual-drainage approach is appropriate for real-time applications.

Further insight into the mechanism of heavy metals partitioning in stormwater runoff.

Various particles and materials, including pollutants, deposited on urban surfaces are washed off by stormwater runoff during rain events. The interactions between the solid and dissolved compounds in stormwater runoff are phenomena of importance for the selection and improvement of optimal stormwater management practices aimed at minimizing pollutant input to receiving waters. The objective of this research was to further investigate the mechanisms responsible for the partitioning of heavy metals (HM) between the solid and liquid phases in urban stormwater runoff. The research involved the collection of samples from urban asphalt surfaces, chemical characterization of the bulk liquid samples, solids separation, particle size distribution fractionation and chemical and physico-chemical characterization of the solid phase particles. The results revealed that a negligible fraction of HM was present in the liquid phase (less than 3% by weight), while there was a strong correlation between the total content of heavy metals and total suspended solids. Examinations of surface morphology and mineralogy revealed that the solid phase particles consist predominantly of natural macroporous materials: alpha quartz (80%), magnetite (11.4%) and silicon diphosphate (8.9%). These materials have a low surface area and do not have significant adsorptive capacity. These materials have a low surface area and do not have significant adsorptive capacity. The presence of HM on the surface of solid particles was not confirmed by scanning electron microscopy and energy dispersive X-ray microanalyses. These findings, along with the results of the liquid phase sample characterization, indicate that the partitioning of HM between the liquid and solid phases in the analyzed samples may be attributed to precipitation processes.

The influence of digital elevation model resolution on overland flow networks for modelling urban pluvial flooding.

This paper presents the developments towards the next generation of overland flow modelling of urban pluvial flooding. Using a detailed analysis of the Digital Elevation Model (DEM) the developed GIS tools can automatically generate surface drainage networks which consist of temporary ponds (floodable areas) and flow paths and link them with the underground network through inlets. For different commercially-available Rainfall-Runoff simulation models, the tool will generate the overland flow network needed to model the surface runoff and pluvial flooding accurately. In this paper the emphasis is placed on a sensitivity analysis of ponds and preferential overland flow paths creation. Different DEMs for three areas were considered in order to compare the results obtained. The DEMs considered were generated using different acquisition techniques and hence represent terrain with varying levels of resolution and accuracy. The results show that DEMs can be used to generate surface flow networks reliably. As expected, the quality of the surface network generated is highly dependent on the quality and resolution of the DEMs and successful representation of buildings and streets.

Automatic, semi-automatic and manual validation of urban drainage data.

Advances in sensor technology and the possibility of automated long distance data transmission have made continuous measurements the preferable way of monitoring urban drainage processes. Usually, the collected data have to be processed by an expert in order to detect and mark the wrong data, remove them and replace them with interpolated data. In general, the first step in detecting the wrong, anomaly data is called the data quality assessment or data validation. Data validation consists of three parts: data preparation, validation scores generation and scores interpretation. This paper will present the overall framework for the data quality improvement system, suitable for automatic, semi-automatic or manual operation. The first two steps of the validation process are explained in more detail, using several validation methods on the same set of real-case data from the Belgrade sewer system. The final part of the validation process, which is the scores interpretation, needs to be further investigated on the developed system.

Uncertainty reduction in water distribution network modelling using system inflow data

In water distribution network (WDN) modelling, nodal demand is the sum of flows taken by users associated with a computational node. User demands are not fixed in time; rather they are stochastic. Hence, nodal demand is a model parameter with high uncertainty, which is propagated throughout the WDN model, thus also rendering the output values (node pressures and pipe discharges) uncertain. Total water inflow into the network can be accurately measured using flow meters. This paper investigates how knowledge of system inflow can be used as a constraint in WDN modelling, taking into consideration the uncertain nodal demands, and consequently reducing the uncertainty of the model output. Fuzzy sets were used to represent the uncertain demands and modified genetic algorithms were used to find the optimal solutions. As a test case, a set of data from a real WDN was used. The uncertainty of the WDN model output was computed for two cases: first, with the total network inflow taken into consideration; and second, with the inflow used as a constraint. Although the methodology that handles the constraints needs significantly greater computational effort, its results provide a more realistic insight into model uncertainty. The proposed methodology was verified using Monte Carlo simulation.

Improving merge methods for grid-based digital elevation models

Digital Elevation Models (DEMs) are used to represent the terrain in applications such as, for example, overland flow modelling or viewshed analysis. DEMs generated from digitising contour lines or obtained by LiDAR or satellite data are now widely available. However, in some cases, the area of study is covered by more than one of the available elevation data sets. In these cases the relevant DEMs may need to be merged. The merged DEM must retain the most accurate elevation information available while generating consistent slopes and aspects. In this paper we present a thorough analysis of three conventional grid-based DEM merging methods that are available in commercial GIS software. These methods are evaluated for their applicability in merging DEMs and, based on evaluation results, a method for improving the merging of grid-based DEMs is proposed. DEMs generated by the proposed method, called MBlend, showed significant improvements when compared to DEMs produced by the three conventional methods in terms of elevation, slope and aspect accuracy, ensuring also smooth elevation transitions between the original DEMs. The results produced by the improved method are highly relevant different applications in terrain analysis, e.g., visibility, or spotting irregularities in landforms and for modelling terrain phenomena, such as overland flow. A new merge method for raster data sets, called MBlend, is presented.MBlend is tested in two areas in the UK, using four different elevation data sets.MBlend is compared with conventional raster data sets merging methods.MBlend produces smoother transitions between the raster data sets being merged.MBlend retains the information of the most accurate and detailed raster data set.

Hydrodynamic effects of debris blockage and scour on masonry bridges: Towards experimental modelling

This paper describes the preliminary stage of an ongoing project investigating the hydrodynamic effects of debris blockage at masonry bridges. Debris blockage is cited as one of the primary causes of bridge failures in the UK and around the world. Masonry bridges, many of which are valuable historical assets, are particularly vulnerable to debris blockage due to their short spans and low clearance. This paper presents work done as part of the first phase of the project involving experimental research to understand the scientific relationships between debris characteristics and flow conditions. The study, being carried out at Centre for Water Systems at University of Exeter, utilizes a 0.6m-wide and 10m-long flume to run hydraulic experiments in order to characterize the impact of debris blockage on flow hydrodynamics, scour, and hydrodynamic pressures and forces at masonry bridges. This paper outlines the design of the experimental setup and the reasoning behind the choices for preliminary experimental parameters. The experiments are to include testing of bridge models and various 3D-printed debris shapes under realistic flow conditions. Geometry of the bridge and debris models are kept approximately similar to prototype conditions, with hydraulic conditions of the experiments designed to the degree that experimental constraints allow based on Froude similarity. Velocities, scour and hydrodynamic pressures are measured using an Acoustic Doppler Velocimeter, echo-sounding concept and pressure sensors, respectively. Preliminary results indicate that the designed experiments have the potential to enhance our understanding of the hydrodynamic effects of debris blockage.

Build-up and characterisation of pollutants on urban impervious surfaces

This paper presents the results of the investigation of pollutant build-up on impervious surfaces of a parking lot in Belgrade, Serbia during the summer months. Contaminant build-up was found to be greater on asphalt surfaces directly exposed to vehicular traffic than on concrete walkways. The difference in the amounts of accumulated pollutants between asphalt and concrete were significant: for total solids (TS), total suspended solids (TSS), chemical oxygen demand (COD), heavy metals and total phosphorus (TP) accumulations were two to three times higher, while only 30% higher for total nitrogen (TN) and anions. Build-up of most of the measured parameters was best described by power functions. The highest surface loads were found for solids, COD, iron and zinc. A strong correlation was found between turbidity, TS, TSS, COD, heavy metals and phosphorus, while conductivity, nitrates and nitrites were weakly correlated to other parameters.

Cellular Automata Approach for 2D Pollution Transport Modelling in Urban Groundwater

Integrated modelling requires many simplifications in order to speed up long time calculations and simulations. Therefore, many non-traditional methods are being widely used. Cellular automata (CA) represents one of these methods. The paper presents the application of the CA approach in modelling of the contaminant transport in unsteady groundwater conditions. It compares the results obtained using the two CA models modified for groundwater problems. Results obtained in this paper show that CA approach can be successfully used for simulations of unsteady groundwater conditions, caused by surface-groundwater interaction, and pollution transport.

Electro-Magnetic Velocity Meters: Assessment of the (Missing) Technical Parameters

Flow measurements in Urban Drainage Systems are essential for the pollution control. Since the accuracy of the Acoustic Doppler Velocimeters is impeded by several factors, this research is focused on the alternative or a supplemental Electro-Magnetic Velocity (EMV) meters. EMV meters are more robust and reliable and can provide accurate measurements of low flows or even under a porous sediment cover. However, the downside of their usage is the small control volume (CV) where the flow velocities are integrated in a non-linear manner to obtain a single one-dimensional velocity measurement. To provide accurate mean flow velocity it is necessary to determine the size of the CV and to understand the non-linear integration principle within the CV. These valuable data are typically not provided by the manufacturer. In this paper, an experimental methodology is proposed for defining the size of the CV and the one-dimensional (1D) weighting function, used to describe the sensor’s integration principle. In the experiments, bed-mounted flat DC2 EMV probe was used. The size of the CV and 1D weighting function were determined based on the results of the EMV operation under sand cover of varying depth. It was shown that the reach of the CV for the used device is 6 cm from the electrodes of the sensor.