**4. Conclusions**

This study compared the infiltration capacity of the rain gardens at Bryggen with international guidelines [41–45]. It compares small-scale MPD tests to full-scale infiltrations test and further evaluate if the rain garden is preforming as designed. The full-scale infiltration test showed an increase of the groundwater level in several boreholes at Bryggen.

The rain garden and its connected infiltration systems function for the purpose it is built, to infiltrate stormwater into the subsurface to increase the soil moisture as well as groundwater level to protect the cultural layers in the subsurface. The hydraulic conductivity of the SuDS is as designed with an infiltration capacity of 500–1600 mm/h. This study shows that the full-scale infiltration test gives a higher infiltration capacity of the rain gardens, compared to small-scale tests. The e ffect of the infiltrated volume and the natural precipitation influence the groundwater level, with an immediate response in monitoring wells close to the infiltration system (<30 m) and with a time delay of ca. 2 days in wells 75–100 m away from the infiltration point. The infiltration capacity of the rain garden exceeds the amount of available surface water currently connected to the system. The groundwater level would, in dry periods, benefit from more consistent water input to increase soil moisture and thereby preserve cultural layers below. There is excess capacity, and the connected runo ff catchment area can be extended to encompass the total catchment area by 22,500 m<sup>2</sup> or 260 precent (%). There is a need to document the e ffect of SuDS on the urban water cycle. This study shows how monitoring systems can be implemented in designing and planning, which could help stormwater managers with the scheduling of maintenance requirements for rain gardens with more confidence.

**Author Contributions:** Conceptualization, G.V. and F.C.B.; methodology, F.C.B.; validation, G.V. and F.C.B.; formal analysis, G.V. and F.C.B.; investigation, G.V.; data curation, G.V.; writing—original draft preparation, G.V.; writing—review and editing, F.C.B. and G.V.; visualization, G.V. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research is supported through the JPI Water funded INXCES research project "Innovation for eXtreme Climatic EventS" www.inxces.eu. INXCES exchange researchers, methodology and results on an international level, with the aim is to share research results with stakeholders and set up guidelines for design, implementation and maintenance of SuDS to promote sustainable water managemen<sup>t</sup> systems throughout the world. Within the INXCES project knowledge exchange between disciplines and nations is in focus.

**Acknowledgments:** Great appreciation to Torstein Dalen at the Water and Wastewater department at Bergen Municipality for help and contributions. Thanks to the Bryggen project for access to borehole data http: //prosjektbryggen.no. We thank Bergen Municipality and Hanze University of Applied Sciences Groningen, Deltares and the Geological Survey of Norway for support for this work. Thanks to Riksantikvaren (Directorate for Cultural Heritage) and NIKU (Norwegian Institute for Cultural Heritage) for making data freely available. Thanks to Norwegian Hydrology Council for the NHC2018 conference in Bergen, and this special conference issue. Great appreciation to Malin Andersson at the Geological Survey of Norway (NGU) for constructive feedback on this paper.

**Conflicts of Interest:** The authors declare no conflict of interest.
