# Delineation of the Flooded Areas in Urban Environments Based on a Simplified Approach
## 6 Conclusions  
As stated by [PERSON] et al. (2021), the ungauged basins are those basins completely or partially lacking hydrometric observations and, consequently, unable to support calibration procedures for hydrological modelling. In the case of the Tulcea municipality, no outlet discharges had been measured in the past two decades. This is likely the situation with other towns in Romania and in other countries. The urban floods in the Tulcea municipality are due to a combination of influencing factors: torrential rains, city topography (sudden transition from a high slope to a lower slope), complicated street pattern, faulty sewerage design, and maintenance of old sewer collectors (angles of 90 degrees along the sewage system and insufficient designed capacity). The floods generated by torrential rainfalls occur in the meadow area, which is characterized by a lower slope vs. the slope of the surrounding hills. The runoff rainwater is directed quickly to the lower urban parts, where waters lose their speed and stagnate on the surface of the land. Regarding the applicability of the herein presented method, a major issue is the reliance solely on crowdsourced data for calibrating the outcome of the hydrological models, as no reliable information exists regarding the discharge series at the outlets of the urban storm drainage system. The use of crowdsourced data for calibrating the urban hydrological models, based mainly on the accumulated runoff volumes in the depression areas and not necessarily on peak discharge, is a quite recent approach. The case study on the Tulcea municipality and the corresponding model plainly reveal key aspects of the method and its possibilities for application. Such insights refer to the use of crowdsourced data circumstantially obtained by various means (mass-media, internet, social media, etc). For instance, the landmarks or other relevant elements with known heights (such as cars and first-floor levels) in a specific area are valuable information to estimate the water level or the water height. Based on the Digital Terrain Model and GIS tools, the estimated water levels within the urban environment can be mapped and the flood extent can be obtained, allowing various runoff volume analyses. Depending on the local topography, the low areas (depressions) where the water is expected to accumulate can be parcelled out at the water divide, in a number of so-called flood cells, for which a volume-elevation curve can be predetermined using DTM. A flood cell can be fed by one or multiple urban catchments. The volume-elevation curve determined for each flood cell can be used to obtain the flood extent for various scenarios (use of different design storms with various frequencies, changes in runoff, or CN values, implementation of green measures, or complementary SUDS in different sub-catchments, etc.). The accuracy of this approach (calibrating the hydrological model by using crowdsourced data, together with DTM pre-processing) is mainly preserved by the accuracy of the generated DTM (horizontal resolution/vertical accuracy) and by the type of the hydrological model employed. An increase in the DTM resolution and vertical accuracy will provide more accurate results regarding flood extent and potential runoff volumes accumulated on the terrain surface. If a simple hydrological model is used (case in this paper), the results will have a lesser accuracy. A distributed hydrological model, linked with the storm urban drainage system, will always provide better results in terms of accuracy, but at the same time will require a significant amount of data and greater computational power and time. The approach proposed in this paper has been conceived as a methodology that uses a minimum amount of data while providing reasonably good results in the shortest time period. This lack of measured functional discharges at the outlets of the urban sewage system may generate quite significant uncertainties regarding the obtained result quality as well as the effectiveness of the approach.