The increase of pluvial flooding has long been discussed to be a most probable outcome of climate change. This has raised the question of necessary consequences in the design of urban drainage systems in order to secure adequate flood protection and resilience. Due to the uncertainties in future trends of heavy rainfall events, the awareness of remaining risks of extreme pluvial flooding needs to be roused at responsible decision makers and the public as well leading to the implementation of pluvial flood risk management (PFRM) concepts. The state of two core elements of PFRM in Germany are described here: flood hazard and risk evaluation and risk communication. In 2016 the guideline DWA‐M 119 has been published to establish city‐based PFRM concepts in specification of the European Flood Risk Management Directive (EU 2007). As core elements, the guidelines recommend a site‐specific analysis and evaluation of flood hazards and potentials of flood damages to create flood hazard and flood risk maps. In the long run, PFRM needs to be established as a joint community effort and a requirement for more flood resilience. The risk communication within the administration and in the public requires a comprehensible characterization and classification of heavy rainfall to illustrate event extremity. The concept of a rainstorm severity index (RSI) instead of statistical rainfall parameters appears to be promising to gain a better perception by affected citizens and non‐hydrology‐experts as well. A methodical approach is described to specify and assign site‐specific rainfall depths within the severity index scheme RSI12. This article is categorized under: Engineering Water > Sustainable Engineering of Water Engineering Water > Planning Water Engineering Water > Methods

Tracking waterborne microplastic (MP) in urban areas is a challenging task because of the various sources and transport pathways involved. Since MP occurs in low concentrations in most wastewater and stormwater streams, large sample volumes need to be captured, prepared, and carefully analyzed. The recent research in urban areas focused mainly on MP emissions at wastewater treatment plants (WWTPs), as obvious entry points into receiving waters. However, important transport pathways under wet‐weather conditions are yet not been investigated thoroughly. In addition, the lack of comprehensive and comparable sampling strategies complicated the attempts for a deeper understanding of occurrence and sources. The goal of this paper is to (i) introduce and describe sampling strategies for MP at different locations in a municipal catchment area under dry and wet‐weather conditions, (ii) quantify MP emissions from the entire catchment and two other smaller ones within the bigger catchment, and (iii) compare the emissions under dry and wet‐weather conditions. WWTP has a high removal rate of MP (>96%), with an estimated emission rate of 189 kg/a or 0.94 g/[population equivalents (PEQ · a)], and polyethylene (PE) as the most abundant MP. The specific dry‐weather emissions at a subcatchment were ≈30 g/(PEQ · a) higher than in the influent of WWTP with 23 g/(PEQ · a). Specific wet‐weather emissions from large sub‐catchment with higher traffic and population densities were 1952 g/(ha · a) higher than the emissions from smaller catchment (796 g/[ha · a]) with less population and traffic. The results suggest that wet‐weather transport pathways are likely responsible for 2–4 times more MP emissions into receiving waters compared to dry‐weather ones due to tire abrasion entered from streets through gullies. However, more investigations of wet‐weather MP need to be carried out considering additional catchment attributes and storm event characteristics.

The occurrence of microplastic in terrestrial and water environments can be traced back to anthropogenic activities. Urban drainage systems play a role in transporting microplastic from urban sources into receiving waters or soils. The analysis (including sampling, sample preparation and detection) of microplastic are very complex and time-intensive, and sampling alone is the main contributor to uncertainty in the process. However, the lack of representative and comparable sampling strategies complicates the efforts to quantify emitted loads and to identify sources and pathways. Therefore, strategies for sampling microplastic in different wastewater compartments were developed and tested. The ongoing phase, however, focuses on sampling stormwater runoff in separate sewer systems. A new autonomous sampling concept for stormwater was designed and implemented to capture large sample volumes. The sample volume plays an important role with respect to the representativeness. Samples are then prepared, both in situ and in laboratory to produce five size fractions (1000, 500, 100, 50, 5 μm). Preliminary results show that urban drainage systems transport different loads of at least four microplastic types; namely polyethylene (PE), styrene-butadiene rubber (SBR)1, polypropylene (PP) and polystyrene (PS). High PE concentrations are detected in all stormwater samples, followed by SBR, a main tire wear constituent. SBR loads showed dependency to the number of dry-weather days prior to sampled rain events.

In recent years, thermoextraction/desorption‐gas chromatography/mass spectrometry (TED‐GC/MS) has been developed as a rapid detection method for the determination of microplastics (MP) mass contents in numerous environmentally relevant matrices and, in particular, for the measurement of polymers in water samples without time‐consuming sample preparation. The TED‐GC/MS method was applied to investigate a typical European municipal wastewater system for possible MP masses. Such investigations are important in view of the recent revision of the Urban Wastewater Treatment Directive. Four different representative sampling sites were selected: greywater (domestic wastewater without toilet), combined sewer, and influent and effluent of a wastewater treatment plant (WWTP). All samples were collected by fractional filtration. Filtration was carried out over mesh sizes of 500, 100, 50, and in some cases, 5 µm. Polyethylene (PE), polypropylene (PP), and polystyrene (PS) were detected in all samples, with the PE fraction dominating in all cases. Styrene‐butadiene rubber which serves as an indication of tire abrasion, was only found in the influent of the WWTP. The highest MP mass contents were found in the combined sewer, so MP can become a source of pollution during heavy rain events when the capacity limits of the effluent are reached, and the polluted effluent is released uncontrolled into the environment. Based on the studies, MP retention from the WWTP could be estimated to be approximately 96%. Few trends in polymer type or mass contents were detected within the different fractions of the samples or when comparing samples to each other.