Sustainable urban drainage systems (SuDS) or nature-based solutions (NBSs) are widely implemented to collect, store and infiltrate stormwater. The buildup of pollutants is expected in NBSs, and Dutch guidelines advise monitoring the topsoil of bio-swales every 5 years. In the Netherlands, almost every municipality has implemented bio-swales. Some municipalities have over 300 bio-swales, and monitoring all their NBSs is challenging due to cost and capacity. In this study, 20 locations where bio-swales with ages ranging between 10 and 20 years old were selected for a field investigation to answer the following question: is the soil quality of bio-swales after 10 years still acceptable? Portable XRF instruments were used to detect potential toxic elements (PTEs) for in situ measurements. The results showed that for copper (Cu), zinc (Zn) and lead (Pb), 30%, 40% and 25% of the locations show values above the threshold and 5%, 20% and 0% above the intervention threshold, meaning immediate action should be taken. The results are of importance for stakeholders in (inter)national cities that implement, maintain, and monitor NBS. Knowledge of stormwater and soil quality related to long-term health risks from NBS enables urban planners to implement the mostappropriate stormwater management strategies. With these research results, the Dutch guidelines for design, construction, and maintenance can be updated, and stakeholders are reminded that the monitoring of green infrastructure should be planned and executed every 5 years.
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Stormwater runoff has severe negative and direct impact on the quality of surface waters and groundwater. The impact can cause chemical and heavy-metal pollution. Applying well established methods to map pollutants in urban areas and specifically in Nature-Based Solutions (NBS), such as Sustainable UrbanDrainage Systems (SuDS) is a step towards improving the water quality in the urban water cycle. Traditional mapping of pollutants by the means of soil samples is costly, which is the main reason why the environmental-technical functioning of rainwater facilities has not been investigated on a large scale andsystematically. X-ray fluorescence (XRF) is a known analysing method for finding metals and other components, for laboratory analysis and portable instruments. In this work we propose a new approach of mapping method for pollutants in-situ, such as heavy metals in soil in SuDS, with case studies from theNetherlands where swales were implemented 20 years ago. In situ XRF measurements is a quick and costefficient analysis for heavy meatal mapping in the respect to contaminated soil. In situ XRF measures of various elements, including heavy metals is carried out in a quickscan and accurate manner and measures both qualitatively and quantitatively. It makes the time-consuming and costly interim analyses by laboratories superfluous. In this study, we suggest a new methodology approach for in situ mapping of pollutants in various swales that were implemented from 20 to 5 years ago. The results differ due to multiple factors (age, use of materials, storage volume, maintenance, run off quality, etc.). Several locations reached unacceptable levels, above the national thresholds for pollutants. The spatial distribution of pollutants in the over 30 swales mapped in the Netherlands show that the preferred water flow in theSuDS controls the spreading of pollutants. The swales investigated are presented in an interactive way with the open source tool www.climatescan.nl, containing more than 100 swales, part of which has been investigated with in situ XRF measurements. The research results are of great importance for all stakeholders in (inter)national cities that are involved in climate adaptation. SuDS is the most widely used method for storing stormwater and infiltrating in the Netherlands. However, there is still too little knowledge about the long-term functioning of the soil of these facilities.
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Malmö is well known within the field of urban hydrology, as the city was a pioneer in integrated water management (Stahre 2008). In 1998 the Augustenborg neighbourhood was refurbished due to its reoccurring problems with flooding anddamage caused by water (Niemczynowicz 1999). The project “Ekostaden” (Eco-city) included many initiatives implementing nature-based solutions (NBS), such as swales and rain gardens for infiltrating surface (storm) water into the ground (Climate Adapt 2016) (Figure 1). International stakeholders want to know if these NBS still function satisfactorily after 20 years and what we can learn from the “Augustenborg strategy” and apply in other parts of the world. To quote the German philosopher Georg Wilhelm Friedrich Hegel, “we learn from history that we do not learn from history.” Augustenborg is an ideal location to demonstratethe sustainability of NBS, test the functionality for infiltration of surface water in swales, map the build-up of potential toxic elements (PTE), and test the water quality after 20 years operation. This evaluation is done in 2019 with theinternational, participatory and multidisciplinary method ‘ClimateCafé and the results are presented at the international seminar Cities, rain and risk,June 2019 in Malmö (Boogaard et al. 2019). ClimateCafé is a field education concept involving different fields of science and practice for capacity building in climate change adaptation. Over 20 ClimateCafés have already been carriedout around the globe (Africa, Asia, Europe), where different tools and methods have been demonstrated to evaluate climate adaptation. The 25th edition of ClimateCafé took place in Malmö, Sweden, in June 2019 and focussed on the Eco-city of Augustenborg. The main research question - “Are the NBS in Augustenborg still functioning satisfactorily?”- was answered by interviews, collecting data of water quality, pollution, NBS and heat stress mapping, and measuring infiltration rates (Boogaard et al. 2020).
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