# Delineation of the Flooded Areas in Urban Environments Based on a Simplified Approach
## 5 Discussion  
To reduce the risk of flooding in the central area of Tulcea, the best approach would be a Sponge City solution. However, it was considered that, due to the high slopes of the hills and the short concentration time, such a solution does not offer spectacular and immediate results. A partial solution with lasting effects can be obtained by developing a curtain of vegetation on the hills around the city and by increasing the number of green areas in the municipality. The introduction of interception collectors at the middle of the slope is another solution to reduce the flow that reaches the base of the slope. They must be designed so that they can fully take over the upstream flow. However, the local administration demanded quick results, opting for a grey infrastructure solution accompanied by the development of green solutions over time. The results obtained with IDF 1:5 design rainfall were used as a basis for proposing discharging or temporary retention solutions. Two solutions which utilise underground storage tanks at the most sensitive areas of Tulcea, namely the areas of objects 2, 3, 4, 5, 6, and 7, have been proposed (Figure 22). The tanks, equipped with pumping stations, are located under the streets in the area of the previously mentioned objects. In Solution-1, runoff urban water flow from the two urban areas which have experienced flooding problems (Babadag-Unirii and Pacii-Antipa-Isaccei) is collected at the same point, and only one pumping station is attached to the urban sewage system. Powerful pumps must be considered in order to deal with various situations that may arise in operation (e.g., increased water levels in the Danube or higher flood volumes than the volume of the tank). In Solution-2, it is potentially possible to use the existing pumping station (SPAP 3), but this must certainly be reviewed. In this configuration, the tanks are independent and do not intercommunicate. A slightly unfavourable situation compared to Solution-1 is given by the lack of a tank in the Isaccea street, in the urban sector confined between Unirii and Pacii streets. The analysis and pre-sizing of the proposed tanks were broken down, depending on the area in which they are located. In Solution-1, the length of the tank under Unirii street (for objects 2, 3, and 4) is approx. 209 m, with an inner height of 3 m, and an inner width of 10 m (the street width). The carrying capacity of this tank is 14.7 m\({}^{3}\)/s. The tank on Isaccea street (objects 5 and 6) has the following dimensions: length 146 m, inner height 3 m, and 8 m width, with a carrying capacity of 10.8 m\({}^{3}\)/s. The two previous tanks are connected to  
Figure 22: Proposed solutions for flood mitigation: **(a)** Solution-1 and **(b)** Solution-2. Legend: blue line = proposed tanks; green rectangle = pumping station. the third tank located near the Delta Hotel parking (Objects 2, 3, 4, 5, and 6) so that the flow rates and volumes will be summed up for proper dimensioning. The carrying capacity should be 25.5 m\({}^{3}\)/s. As it is located in the wider park near Delta hotel, its inner width can be 16 m, the interior height 3 m, and the length is 76 m. The slope of all the tanks is 0.5%, chosen according to the average level of the Danube. A similar analysis was performed for Solution-2. Being less favourable than Solution-1, its tank dimensions are not detailed herein. The total volume that can be accumulated in the tanks in Solution-1 is Vtotal = 13,422 m\({}^{3}\), as compared to Solution-2, where Vtotal = 12,240 m\({}^{3}\). In both cases, pumping stations are required in the downstream area. Both solutions proposed for discharging the urban runoff towards the Danube must be accompanied by additional works (a better drainage of surface water into the sewer system and resizing of collectors, especially on streets such as Lieutenant Gavrilov, etc.). Particular attention should be paid to the limited (non-clogged) drainage capacity of the grate inlets, which is only 11 L/s.