# Delineation of the Flooded Areas in Urban Environments Based on a Simplified Approach
## 6 Conclusions
For this case study, only two flooding events were available, and more crowdsourced data would be necessary to guarantee the stability of the derived parameters. In order to compensate for the lack of outlet discharge information, two extreme rainfall scenarios were analysed, considering the functionality of the urban drainage system (1) as entirely out of function and (2) as operating at its design capacity, respectively. The calibration and validation were based on only the estimated volumes in the depression areas, meaning a DTM which has an adequate horizontal resolution and vertical accuracy is compulsory. Better DTM data will ensure a better representation of the flooding extent and of the accumulated volumes on the terrain surface, even if only crowdsourced data are available. Another major reason for using a high-quality DTM is for accurately deriving the surface flow directions (through GIS analysis). The urban configuration does usually bring in major deviations to the runoff flow directions. Hydrological analysis in a natural catchment does not necessarily require a high-resolution DTM, but the same analysis in urban areas does require a high-quality DTM. For the evaluation of the excess rainfall, a lumped hydrological model used in conjunction with a volume-based operand flood analysis was preferred due to the lack of detailed data related to the sewage network and the fast still-reliable results that can be obtained over a large number of simulations. Considering the results based on the available data, it can be considered that the models are satisfactorily calibrated. The accuracy of the results is indirectly confirmed by the extension of the flooded areas determined for the September 2013 event. The results obtained for the event of June 2016 show a deficient functioning of the sewage system in the area of objects 2, 3, 4, 5, and 6 due to multiple causes, such as flow exceeding the carrying capacity of the system or partial clogging of the inlet grills or of system's various collectors. Under the specific conditions of the Tulcea municipality, large-capacity retention tanks (equipped with powerful pumps to discharge rainwater directly into the Danube), were considered for the lower part of the municipality where the capacity of the drainage network appears to be exceeded. This solution will be progressively supported by a set of green measures, with their due implementation over time. The implementation of LID measures, by considering retrofitting opportunities for the local land use, will improve the efficiency of the proposed DTs, with the expected knowledge benefit especially in the perspective of climate change. **Author Contributions:** Conceptualization, R.D. and C.D. ; methodology, R.D. and C.D. ; validation, N.S. ; investigation, N.S. ; data curation, N.S. ; writing--original draft preparation, C.D. ; writing--review and editing, R.D. ; visualization, C.D. ; supervision, R.D. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was undertaken in the work frame of LIOP (Large Infrastructure Operational Programme), Project Code SMIS 2014+ 107170, funded 85% by Cohesion Fund, 14% State Budget and 1% Local Budget of Tulcea County. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Data sharing was not applicable to this study. **Acknowledgments:** The authors are indebted to [PERSON] (Senior Dutch International Expert/NL) for his pertinent revision of the English version of this paper. **Conflicts of Interest:** The authors declare no conflict of interest.