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Urban Water InterfacesW2 -Scaling and connectivity assessment of critical source areas of diffuse pollution in urban catchments

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W2 - Scaling and connectivity assessment of critical source areas of diffuse pollution in urban catchments

Doctoral student: Nasrin Haacke

Supervisors: Prof. Dr. Eva Paton, Dr. Thomas Nehls, Prof. Dr. Reinhard Hinkelmann

Introduction / Background

Urban areas contain numerous diffuse sources of contaminants, which are mobilized during rainfall and discharged into urban drainage systems or directly into nearby surface waterbodies. Surfaces of building material, streets, pavements and green spaces present only a few important sources of diffuse pollution, which are exposed to wash-off and leaching processes driven by rainfall (Wicke et al. 2015, Müller et al. 2019). Although many studies exist on pollution sources (Pitt et al. 2005, Ellis and Mitchell 2006, Göbel et al. 2007), only few studies deal with the spatial patterns that influence urban diffuse pollution. This can be explained by diverse factors affecting the distribution and magnitude of contaminant releases, e.g. pollution source characteristics, urban surface cover and sealing, the intensity, duration and timing of rainfall events (Göbel et al. 2007). Therefore, it is a challenge to research on urban water pollution to investigate how pollutants are mobilized and transferred within complex urban spaces/landscapes, especially during high-intensity storms.

Aims and objectives

The aim of this project is an advanced hierarchy and connectivity assessment of critical contaminant source areas in urban catchments under a changing regime of high-intensity storms. Project work includes a statistical analysis of extreme rainfall events of short duration (1min up to 1h) for multiple cities across Germany (WP1) and the quantification of contaminant concentrations from critical and emerging urban surface types using rainfall simulation experiments (WP2). The data and information obtained in WP1 and WP2 will be used to improve and evaluate the accuracy of storm water quality modelling in urban catchments (WP3). Upscaling methods of contaminant retention or export towards urban rivers and lakes will be developed to derive new, sustainable water resource management options for cities.

Methods

The focus of the first objective was to investigate the diurnal, seasonal and annual occurrence of extreme rainfall events of short-duration (10min and 1h) with a return period of 5 years for numerous meteorological stations across Germany. An additional analysis considering 5 meteorological stations was carried out for the city of Berlin (Fig.1) to identify intra-city variation of urban flash floods. The statistical analyses and data processing (development of sorting algorithm) was done with R (R Core Team 2018) based on datasets of long-term precipitation measurements provided by the German Meteorological Service (DWD). Extremes were selected using two different approaches: the 99th percentile after Weder et al. (2017) and the peak over threshold-value. The latter is based on KOSTRA (Fig.2, Malitz and Ertel 2015).

Fig.1: Diurnal, seasonal and annual occurrence of extreme rainfall events in the upper 99th percentile plotted for 5 stations in Berlin Blue line marks minimum precipitation value for a 10 min rainfall event, black line for an 1 h rainfall event with a return interval of 5 years, respectively.
Lupe

Results

The distribution patterns in Figure 1 show that high spatiotemporal variability of rainfall extremes is evident in Berlin on all investigated time scales. For the study area this intra-variability can potentially explained by the topographic configuration: measured values on plateaus show on average higher precipitation sums than in the Greater Spree Valley. With these results we can identify critical urban catchments of high precipitation events for rainwater management purposes. Despite strong evidence for climate change in rising average temperatures the analysed data show no observable change in distribution of extreme events. Ongoing statistical analysis on extreme rainfall events across Germany considers the occurrence of large-scale weather patterns causing heavy rainfall during summer.

Fig.2: (a) Distribution of precipitation depths for 10min duration events with a return interval of 5 years across Germany, (b) Berlin and (c) for 1h duration events across Berlin derived from KOSTRA.
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Collaborations

Collaborations within UWI: W1,W3, H4

UWI kollegiates: Franzi Tügel und Basem Aljoumani

External collaborations: BWB

References

Ellis, J.B. and Mitchell, G. (2006). Urban diffuse pollution: key data information approaches for the Water Framework Directive. Water and Environment Journal, Vol. 20, pp. 10-26, doi:

Göbel, P., Dierkes, C. and Coldewey, W.G. (2007). Storm water runoff concentration matrix for urban areas. Journal of Contaminant Hydrology, Vol. 91, pp.26-42.

Malitz, G. and Ertel, H. (2015). KOSTRA-DWD-2010 - Starkniederschlagshöhen für Deutschland (Bezugszeitraum 1951 bis 2010). Final Report, Deutscher Wetterdienst, Offenbach am Main.

Müller A., Österlund, H., Nordqvist, K., Marsalek, J. and Viklander, M. (2019). Building surface materials as sources of micropollutants in building runoff: A pilot study. Science of The Total Environment, Vol. 680, pp. 190-197.

Pitt, R., Bannerman, R., Clark, S. and Williamson, D. (2005). Sources of Pollutants in Urban Areas (Part 2) – Recent Sheetflow Monitoring. In: Effective Modeling of Urban Water Systems.

R Core Team (2018). R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna.

Weder, C., Müller, G. and Brümmer, B. (2017). Precipitation extremes on time scales from minute to month measured at the Hamburg Weather Mast 1997–2014 and their relation to synoptic weather types. Meteorologische Zeitschrift, Vol. 26, pp. 507-524.

Wicke, D., Matzinger, A. and Rouault, P. (2015). OgRe - Relevanz organischer Spurenstoffe im Regenwasserabfluss Berlins. Final Report, Kompetenzzentrum Wasser Berlin, Berlin.

 

 

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