## 3 Results
### Mitigation of Urban Flooding through Basin-Scale NbSs
Interestingly, in the current scenario with the actual soil uses and management (i.e., simulation CN89-A), the infiltration was negligible and attenuated the peak discharge only by 3.9%. Even for the lowest curve number (simulation CN64-A), we found that \(Q_{\rm max}\) decreased slightly from 53.8 to 44.9 m\({}^{3}\).s\({}^{-1}\), which represents a small relative factor of 16.6%. Furthermore, hydrographs A (black lines in Figure 9) nearly overlap those of the simulations type C (green lines in Figure 9). Subsequently, acting on the olive-grove area to improve the infiltration (i.e., decreasing the curve number) and raise the surface roughness (i.e., increasing the Manning parameter), as shown in Figure 4c-e, does not help to attenuate the peak discharge substantially nor delay the inundation in the urban area. In the best case, the streamflow was attenuated by 17.6% (CN64-C) and reached \(Q_{\rm max}=44.3\) m\({}^{3}\).s\({}^{-1}\) with the same concentration time as for scenario A. The increase in the Manning roughness in the olive-tree area (coloured in blue in Figure 4) did not delay the inundation because the water drops had to travel a short distance to reach elements of \begin{table}
\begin{tabular}{l c c c c c c c c c c} \hline  & **A** & **B** & **C** & **D** & **E** & **A** & **B** & **C** & **D** & **E** \\ \hline \multicolumn{10}{c}{\(Q_{\rm max}\) [m\({}^{3}\).s\({}^{-1}\)]} \\ \hline
**CN100** & 53.8 & 51.3 & 53.7 & 53.7 & 23.1 & 44 & 120 & 45 & 94 & 37 \\
**CN89** & 51.7 & 47.8 & 51.5 & 51.0 & 22.2 & 45 & 120 & 46 & 96 & 38 \\
**CN64** & 44.9 & 41.7 & 44.3 & 45.4 & 19.5 & 46 & 120 & 47 & 108 & 41 \\ \hline \multicolumn{10}{c}{Attenuation (\%)} \\ \hline
**CN100** & 4.6 & 0.3 & 0.2 & 57.1 & & 2.7 & 1.0 & 2.1 & 4.1 \\
**CN89** & 3.9 & 11.2 & 4.3 & 5.1 & 58.7 & 1.0 & 2.7 & 1.0 & 2.2 & 4.1 \\
**CN64** & 16.6 & 22.5 & 17.6 & 15.5 & 63.8 & 1.1 & 2.7 & 1.1 & 2.5 & 4.1 \\ \hline \end{tabular}
\end{table} 
Table 1: Peak water discharge \(Q_{\rm max}\) and time of concentration \(T_{\rm sim}\) for the simulated hydrographs in Figure 9. The attenuation of the peak discharge regarding the maximum value of scenario CN100-A and the delay factor of the time to peak flow are also given. Figure 9: Hydrograph at the basin outlet for the fifteen physical scenarios. the drainage network. Such a distance was much shorter than the characteristic lengths of the gullies and streams (green area in Figure 4) that remained unaltered in scenario C concerning A. Promising results were obtained for NbS type B that alters the roughness of the drainage network through riparian buffer installation, boulders, and willow in-ditch barriers, among others. The most noticeable result was the delay of the rising limb, which can be appreciated in the hydrographs of Figure 9 coloured in blue. The concentration-time increased from about 45 min to 120 min, i.e., by a factor of 2.7. On the one hand, the benefits of NbS type B are great during the first hour of the rainfall independently of the CN value because \(4.2\leq Q\leq 5.3\) m\({}^{3}\).s\({}^{-1}\) at \(t=1\) h for \(64\leq CN\leq 100\). Such streamflow values are much lower than for scenarios A and C at the same instant of time, which ranges in the interval \(40.9\leq Q\leq 50.5\) m\({}^{3}\).s\({}^{-1}\). On the other hand, for rainfall durations of 2-3 h, the peak discharge is about \(38.9\leq Q\leq 51.3\) m\({}^{3}\).s\({}^{-1}\), which is closer to the peak values for scenarios A and C. Hence, NbS type B is practical for mitigating the risk of flooding in the town for extreme rains shorter than one hour, but longer events require other NbSs. The installation of a flood barrier to create an artificial wetland (NbS D) and the construction of a large reservoir pond (NbS E), recall Figure 4a,b, stopped the growth of the streamflow at \(t\approx 30\) min as shown by the hydrographs in red and purple (Figure 9), respectively.