Imperial College London


Faculty of EngineeringDepartment of Civil and Environmental Engineering

Research Associate







304Skempton BuildingSouth Kensington Campus





Publication Type

14 results found

Dobson B, Barry S, Maes-Prior R, Mijic A, Woodward G, Pearse WDet al., 2022, Predicting catchment suitability for biodiversity at national scales, WATER RESEARCH, Vol: 221, ISSN: 0043-1354

Journal article

Liu L, Dobson B, Mijic A, 2022, Hierarchical systems integration for coordinated urban-rural water quality management at a catchment scale., Science of the Total Environment, Vol: 806, Pages: 1-12, ISSN: 0048-9697

Managing river quality is important for sustainable catchment development. In this study, we present how catchment management strategies benefit from a coordinated implementation of measures that are based on understanding key drivers of pollution. We develop a modelling approach that integrates environmental impacts, human activities, and management measures as three hierarchical levels. We present a catchment water management model (CatchWat) that achieves all three hierarchical levels and is applied to the Cherwell Catchment, UK. CatchWat simulations are evaluated against observed river flow and pollutant data including suspended solids, total nitrogen, and total phosphorus. We compare three competing hypotheses, or framings, of the catchment representation (integrated, urban-only, and rural-only framings) to test the impacts of model boundaries on river water quality modelling. Scenarios are formulated to simulate separate, combined and coordinated implementation of fertiliser application reduction and enhanced wastewater treatment. Results show that models must represent both urban and rural pollution emissions to accurately estimate river quality. Agricultural activities are found to drive river quality in wet periods because runoff is the main pathway for rural pollutants. Meanwhile, urban activities are the key source of pollution in dry periods because effluent constitutes a larger percentage of river flow during this time. Based on this understanding, we identify a coordinated management strategy that implements fertiliser reduction measures to improve river quality during wet periods and enhanced wastewater treatment to improve river quality during dry periods. The coordinated strategy performs comparably to the combined strategy but with higher overall efficiency. This study emphasises the importance of systems boundaries in integrated water quality modelling and simulating the mechanisms of seasonal water quality behaviour. Our key recommendation is tha

Journal article

Dobson B, WatsonHill H, Muhandes S, Borup M, Mijic Aet al., 2022, A reduced complexity model with graph partitioning for rapid hydraulic assessment of sewer networks, Water Resources Research, Vol: 58, Pages: 1-21, ISSN: 0043-1397

Existing, high-fidelity models for sewer network modelling are accurate but too slow and inflexible for modern applications such as optimisation or scenario analysis. Reduced complexity surrogate modelling has been applied in response to this, however, current approaches are expensive to set up and still require high-fidelity simulations to derive parameters. In this study, we compare and develop graph partitioning algorithms to automatically group sections of sewer networks into semi-distributed compartments. These compartments can then be simulated using sewer network information only in the integrated modelling framework, CityWat-SemiDistributed (CWSD), which has been developed for application to sewer network modelling in this study. We find that combining graph partitioning with CWSD can produce accurate simulations 100-1,000x faster than existing high-fidelity modelling. Because we anticipate that many CWSD users will not have high-fidelity models available, we demonstrate that the approach provides reasonable simulations even under significant parametric uncertainty through a sensitivity analysis. We compare multiple graph partitioning techniques enabling users to specify the spatial aggregation of the partitioned network, also enabling them to preserve key locations for simulation. We test the impact of temporal resolution, finding that accurate simulations can be produced with timesteps up to one hour. Our experiments show a log-log relationship between temporal/spatial resolution and simulation time, enabling users to pre-specify the efficiency and accuracy needed for their applications. We expect that the efficiency and flexibility of our approach may facilitate novel applications of sewer network models ranging from continuous simulations for long-term planning to spatially optimising the placement of network sensors.

Journal article

Jenkins K, Dobson B, Decker C, Hall JWet al., 2021, An Integrated Framework for Risk-Based Analysis of Economic Impacts of Drought and Water Scarcity in England and Wales, WATER RESOURCES RESEARCH, Vol: 57, ISSN: 0043-1397

Journal article

Taylor C, Brodbelt DC, Dobson B, Catchpole B, O'Neill DG, Stevens KBet al., 2021, Spatio-temporal distribution and agroecological factors associated with canine leptospirosis in Great Britain, PREVENTIVE VETERINARY MEDICINE, Vol: 193, ISSN: 0167-5877

Journal article

Ascott MJ, Bloomfield JP, Karapanos I, Jackson CR, Ward RS, McBride AB, Dobson B, Kieboom N, Holman IP, Van Loon AF, Crane EJ, Brauns B, Rodriguez-Yebra A, Upton KAet al., 2021, Managing groundwater supplies subject to drought: perspectives on current status and future priorities from England (UK), Hydrogeology Journal, Vol: 29, Pages: 921-924, ISSN: 0941-2816

Effective management of groundwater resources during drought is essential. How is groundwater currently managed during droughts, and in the face of environmental change, what should be the future priorities? Four themes are explored, from the perspective of groundwater management in England (UK): (1) integration of drought definitions; (2) enhanced fundamental monitoring; (3) integrated modelling of groundwater in the water cycle; and (4) better information sharing. Whilst these themes are considered in the context of England, globally, they are relevant wherever groundwater is affected by drought.

Journal article

Dobson B, Jovanovic T, Chen Y, Paschalis A, Butler A, Mijic Aet al., 2021, Integrated modelling to support analysis of COVID-19 impacts on London's water system and in-river water quality, Frontiers in Water, Vol: 3, Pages: 1-18, ISSN: 2624-9375

Due to the COVID-19 pandemic, citizens of the United Kingdom were required to stay at home for many months in 2020. In the weeks before and months following lockdown, including when it was not being enforced, citizens were advised to stay at home where possible. As a result, in a megacity such as London, where long-distance commuting is common, spatial and temporal changes to patterns of water demand are inevitable. This, in turn, may change where people’s waste is treated and ultimately impact the in-river quality of effluent receiving waters. To assess large scale impacts, such as COVID-19, at the city scale, an integrated modelling approach that captures everything between households and rivers is needed. A framework to achieve this is presented in this study and used to explore changes in water use and the associated impacts on wastewater treatment and in-river quality as a result of government and societal responses to COVID-19. Our modelling results revealed significant changes to household water consumption under a range of impact scenarios, however, they only showed significant impacts on pollutant concentrations in household wastewater were in central London. Pollutant concentrations in rivers simulated by the model were most sensitive in the tributaries of the River Thames, highlighting the vulnerability of smaller rivers and the important role that they play in diluting pollution. Modelled ammonia and phosphates were found to be the pollutants that rivers were most sensitive to because their main source in urban rivers is domestic wastewater that was significantly altered during the imposed mobility restrictions. A model evaluation showed that we can accurately validate individual model components (i.e., water demand generator) and 30emphasised need for continuous water quality measurements. Ultimately, the work provides a basis for further developments of water systems integration approaches to project changes under never-before seen scenarios.

Journal article

Muhandes S, Dobson B, Mijic A, 2021, A method for adjusting design storm peakedness to reduce bias in hydraulic simulations, Proceedings of the Institution of Civil Engineers - Water Management, Pages: 1-31, ISSN: 1741-7589

In the UK, decision makers use hydraulic model outputs to inform funding, connection consent, adoption of new drainage networks and planning application decisions. Current practice requires the application of design storms to calculate sewer catchment performance metrics such as flood volume, discharge rate and flood count. With flooding incidents occurring more frequently than their designs specify, hydraulic modelling outputs required by practice are questionable. The main focus of this paper is the peakedness factor (ratio of maximum to average rainfall intensity) of design storms, adjudging that this is a key contributor to model bias. Hydraulic models of two UK sewer catchments were simulated under historical storms, design storms and design storms with modified peakedness to test bias in modelling outputs and the effectiveness of peakedness modification in reducing bias. Sustainable drainage systems (Suds) were implemented at catchment scale and the betterment achieved in the modelling outputs was tested. The proposed design storm modification reduced the bias that occurs when driving hydraulic models using design storms in comparison with historical storms. It is concluded that Suds benefits are underestimated when using design rainfall because the synthetic rainfall shape prevents infiltration. Thus, Suds interventions cannot accurately be evaluated by design storms, modified or otherwise.

Journal article

Pianosi F, Dobson B, Wagener T, 2020, Use of Reservoir Operation Optimization Methods in Practice: Insights from a Survey of Water Resource Managers, JOURNAL OF WATER RESOURCES PLANNING AND MANAGEMENT, Vol: 146, ISSN: 0733-9496

Journal article

Dobson B, Mijic A, 2020, Protecting rivers by integrating supply-wastewater infrastructure planning and coordinating operational decisions, Environmental Research Letters, Vol: 15, Pages: 1-13, ISSN: 1748-9326

Placing water quality in rivers at the centre of water infrastructure planning and management is an important objective. In response there has been a range of 'whole system' analyses. Few studies, however, consider both abstraction (water removed from rivers) and discharge (water returned) to inform the future planning of water systems. In this work we present a systems approach to analysing future water planning options where system development prioritises the water quality of the receiving river. We provide a theoretical demonstration by integrating water supply and wastewater infrastructure, and downstream river water quality, on an open-source, stylised, systems model for London, UK, at a citywide scale. We show that models which consider either supply or wastewater separately will underestimate impacts of effluent on the water quality, in some cases by amounts that would require £1 billion worth of infrastructure equivalent to mitigate. We highlight the utility of the systems approach in evaluating integrated water infrastructure planning using both socio-economic and environmental indicators. Through this approach we find unintended impacts from planning options on downstream river quality; including benefits from water demand management and rainwater harvesting, and costs from wastewater reuse. Finally, we present a novel management planning option between supply and wastewater, which we refer to as Abstraction-Effluent Dilution (AED), that is, to reduce river abstractions during high precipitation events to dilute untreated sewer spills. The AED option is found to provide up to £200 million worth of equivalent infrastructure in river quality improvements and has minimal impact on the reliability of water supply while requiring only a change in operational decision making. The results highlight that seeing our water systems differently with this holistic approach could fundamentally change the way we think about future water infrastructure plannin

Journal article

Dobson B, Coxon G, Freer J, Gavin H, Mortazavi-Naeini M, Hall JWet al., 2020, The spatial dynamics of droughts and water scarcity in England and Wales, Water Resources Research, Vol: 56, Pages: 1-23, ISSN: 0043-1397

Water scarcity occurs when water demand exceeds natural water availability over a range of spatial and temporal scales. Though meteorological and hydrological droughts have been analyzed over large spatial scales, the impacts of water scarcity have typically been addressed at a catchment scale. Here we explore how droughts and water scarcity interact over a larger and more complex spatial domain, by combining climate, hydrological, and water resource system models at a national scale across England and Wales. This approach is essential in a highly connected and heterogeneous region like England and Wales, where we represent 80 different catchments; 70 different water resource zones; 16 water utility companies; and the water supply for over 50 million people. We find that if a reservoir's storage is in its first percentile (i.e., the volume that is exceeded 99% of the time), then there is, on average, a 40% chance that reservoirs in neighboring catchments will also be at or below their first percentile storage volume. The coincidence of low reservoir storage decays relatively quickly, stabilizing after about 100–150 km, implying that if interbasin transfers are to be provided to enhance drought resilience, they will need to be at least this length. Based on a large ensemble of future climate simulations, we show that extreme droughts in precipitation, streamflow, and reservoir storage volume are projected to worsen in every catchment. The probability of a year with water use restrictions doubles by 2050 and is four times worse by 2100.

Journal article

Dobson B, Wagener T, Pianosi F, 2019, An argument-driven classification and comparison of reservoir operation optimization methods, Advances in Water Resources, Vol: 128, Pages: 74-86, ISSN: 0309-1708

Reservoir operation optimization aims to determine release and transfer decisions that maximise water management objectives such as ensuring a reliable water supply, hydropower production, mitigation of downstream floods, etc. An extensive and growing body of scientific literature exists on advancing and applying mathematical optimization methods to reservoir operation problems. In this paper, we review such literature according to a novel classification system of optimization approaches, which focuses on the characteristics of the actual operation problem – i.e. what needs to be optimized, or in mathematical terms, ‘the argument’ of the optimization problems - rather than the mathematical properties of the optimization algorithm. This enables us to discuss the advantages, limitations and the scope of application of the different optimisation methods; and to provide practical guidelines for matching the properties of a system and operation problem with a suitable optimization method. Alongside this paper we provide code to implement many of the methods we review for an illustrative reservoir system.

Journal article

Dobson B, Wagener T, Pianosi F, 2019, How important are model structural and contextual uncertainties when estimating the optimized performance of water resource systems?, Water Resources Research, Vol: 55, Pages: 2170-2193, ISSN: 0043-1397

Uncertainty in simulating water resource systems (WRSs) makes it difficult to assess how effective different water management decisions will be. Uncertainty in simulation models can undermine the credibility of simulation and optimization studies and the uptake of their results. We identify different sources of uncertainty in WRS models and find that structural uncertainty (i.e., around definition of interrelationships within the system) and contextual uncertainty (i.e., around definition of the system boundaries) are rarely considered when simulating and optimizing WRSs. We propose a methodology to quantify the effects of structural and contextual uncertainties on the estimated performance of optimized water management decisions and demonstrate that they have a significant impact on a real‐world case study of a pumped‐storage system in the UK. To the best of the authors' knowledge, this is the first study to consider the impact of these types of uncertainty on optimized operating policies and their simulated performances. Our main finding is that of all the considered uncertainties, the assumptions made about context—specifically around the level of cooperation between neighboring water companies—had the greatest impact on performance estimates. This is important because few WRSs exist in isolation, yet discussion of the effects that a given definition of the system boundaries have on the simulation/optimization results is uncommon. We also highlight the significance of adequately considering aleatory uncertainty when evaluating performance estimates—something that few studies do—and present a simple technique to justify the sample size used for the evaluation of optimization results.

Journal article

Dobson B, Mijic A, Protecting rivers by integrating supply-wastewater infrastructure planning and coordinating operational decisions, Publisher: California Digital Library (CDL)

Working paper

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