Institute for Technical and Scientific Hydrology Itwh Ltd.

Hannover, Germany

Institute for Technical and Scientific Hydrology Itwh Ltd.

Hannover, Germany
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Jahanbazi M.,Institute for Technical and Scientific Hydrology itwh Ltd | Ozgen I.,TU Berlin | Aleixo R.,GHT Photonics | Hinkelmann R.,TU Berlin
Journal of Hydroinformatics | Year: 2017

One of the approaches to flood modelling is numerical simulation of the diffusive wave approximation of the shallow water equations. Improving these models in various aspects is still an open area of research. In this study, a new diffusive wave model with explicit time integration was developed which includes some novel features: (1) time steps are determined using a novel stability criterion which resulted in more dynamic time steps (i.e., broader range) compared to the conventional Courant-Friedrichs-Lewy stability condition; (2) stability constraints are reduced, considering the flow processes within surface ponds; (3) besides Manning's formula, which is the common equation for computing velocities in diffusive wave models, the free fall velocity and a new equation for wave-front velocity are employed; and (4) the influence of upstream surface ponds on downstream flow is considered. This paper introduces the enhanced diffusive wave model, the socalled Overland Flow Simulator Cellular Automata (OFS-CA), and its results for five test cases. Available analytical solutions and an experimental study were used for verification. Two other shallow water models were used for comparison and benchmarking. Overall, good agreements were observed and OFS-CA was computationally less expensive compared to the other two shallow water models. © IWA Publishing 2017.


Schellart A.,University of Bradford | Liguori S.,University of Bristol | Kramer S.,Institute for Technical and Scientific Hydrology Itwh Ltd. | Saul A.,University of Sheffield | Rico-Ramirez M.,University of Bristol
IAHS-AISH Publication | Year: 2012

Abstract Due to the relatively small spatial scale as well as rapid response of urban drainage systems, the use of quantitative rainfall forecasts for providing quantitative flow forecasts is a challenging task. Due to urban pluvial flooding and receiving water quality concerns it is, however, worthwhile to investigate the potential. In this paper, two radar nowcast models have been compared and used to create quantitative forecasts of sewer flows in the centre of a small town in the north of England. Copyright © 2012 IAHS Press.


Schellart A.,University of Sheffield | Liguori S.,University of Bristol | Kramer S.,Institute for Technical and Scientific Hydrology ITWH Ltd. | Saul A.,University of Sheffield | Rico-Ramirez M.A.,University of Bristol
Hydrological Sciences Journal | Year: 2014

Due to the relatively small spatial scale, as well as rapid response, of urban drainage systems, the use of quantitative rainfall forecasts for providing quantitative flow and depth predictions is a challenging task. Such predictions are important when consideration is given to urban pluvial flooding and receiving water quality, and it is worthwhile to investigate the potential for improved forecasting. In this study, three quantitative precipitation forecast methods of increasing complexity were compared and used to create quantitative forecasts of sewer flows 0-3 h ahead in the centre of a small town in the north of England. The HyRaTrac radar nowcast model was employed, as well as two different versions of the more complex STEPS model. The STEPS model was used as a deterministic nowcasting system, and was also blended with the Numerical Weather Prediction (NWP) model MM5 to investigate the potential of increasing forecast lead-times (LTs) using high-resolution NWP. Predictive LTs between 15 and 90 min gave acceptable results, but were a function of the event type. It was concluded that higher resolution rainfall estimation as well as nowcasts are needed for prediction of both local pluvial flooding and combined sewer overflow spill events. © 2014 IAHS Press.


Jahanbazi M.,Institute for Technical and Scientific Hydrology itwh Ltd. | Egger U.,Institute for Technical and Scientific Hydrology itwh Ltd.
Urban Water Journal | Year: 2014

Two types of dual drainage models were set up to assess urban flooding for a study area in Germany: (1) a static model based on a conventional method in Germany; the overflow volumes of the manholes are gained by the sewer solver HYSTEM-EXTRAN. Using these water volumes and geographic information system (GIS) tools, an overland flow network, composed of flow paths and accumulated water in sinks, is produced, (2) a HYSTEM-EXTRAN 2D model; a two-dimensional (2D) overland flow module is coupled bi-directionally with HYSTEM-EXTRAN. The overland flow and the flow in the sewer system are simulated alternately.Both models were supplied with a synthetic design rainfall and 25 extreme storms. After comparing the models and the results, a practical approach to assess urban flooding is proposed. In this approach the 2D model will compute the depth, extent, and propagation of floods only in the prone areas specified by the static model. © 2014 Taylor & Francis.


Karpf C.,University of Management and Technology | Hoeft S.,University of Management and Technology | Scheffer C.,Institute for Technical and Scientific Hydrology itwh Ltd. | Fuchs L.,Institute for Technical and Scientific Hydrology itwh Ltd. | Krebs P.,University of Management and Technology
Water Science and Technology | Year: 2011

Sewer systems are closely interlinked with groundwater and surface water. Due to leaks and regular openings in the sewer system (e.g. combined sewer overflow structures with sometimes reverse pressure conditions), groundwater infiltration and surface water inflow as well as exfiltration of sewage take place and cannot be avoided. In the paper a new hydrodynamic sewer network modelling approach will be presented, which includes - besides precipitation - hydrographs of groundwater and surface water as essential boundary conditions. The concept of the modelling approach and the models to describe the infiltration, inflow and exfiltration fluxes are described. The model application to the sewerage system of the City of Dresden during a flood event with complex conditions shows that the processes of infiltration, exfiltration and surface water inflows can be described with a higher reliability and accuracy, showing that surface water inflow causes a pronounced system reaction. Further, according to the simulation results, a high sensitivity of exfiltration rates on the in-sewer water levels and a relatively low influence of the dynamic conditions on the infiltration rates were found. © IWA Publishing 2011.

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