## 3 Results
### Distributed Hydrological Simulation of the Catchment in the Present Day  
Figure 6 shows the maps of the flow depth \(h\) (Figure 6a) and the magnitude of the velocity vector \(|\mathbf{u}|\) (Figure 6b) simulated at the time of the peak flow \(t=3\) h for the scenario CN89-A. The flow depth in the tributary streams that drain to the main Manillas stream (green are in Figure 4) reaches values close to 1 m in agreement with the bankfull depth of the actual channels. There, the flow velocity is higher than 1 m\(\cdot\)s\({}^{-1}\), see the orange region in Figure 6b, which is fast. Deeper and even faster flows develop in the downstream reach of the Manillas stream with flow depths and velocities of approximately \(h_{\text{max}}=2.5\) m and \(|\mathbf{u}_{\text{max}}|=5\) m\(\cdot\)s\({}^{-1}\). The flow regime becomes critical with the Froude number \(Fr=|\mathbf{u}_{\text{max}}|/\sqrt{g\,h_{\text{max}}}=1.01\). Regarding the runoff depth, characteristic values are around 2.5 mm (purple colour in Figure 6a) in the southern region draining to the Manillas stream, with high velocities in the range of 0.1-0.4 m\(\cdot\)s\({}^{-1}\) (Figure 6b). Conversely, in the northern area, where the basin slope decreases and the terrain is flatter than in the southern region, the runoff depth is much shallower, and the velocity is slower. Hence, we observe a clear topographic control between the runoff dynamics correlated well with the terrain elevation and slope (Figure 1b). Then, we evaluated the shear-stress vector \(\boldsymbol{\tau}_{b}\) from (3) using the simulated hydraulic variables \(h\) and \(\mathbf{u}\), and drew the map of its magnitude in Figure 6c. The shear stress varies in the wide range of the order of magnitudes from \(10^{-4}\) to \(10^{4}\) N\(\cdot\)m\({}^{-2}\). Figure 6: Map of the maximum values of the (**a**) flow depth \(h\) [m], (**b**) magnitude of the velocity vector \(|\textbf{u}|\) [m\(\cdot\)s\({}^{-1}\)], and (**c**) magnitude of the shear stress vector \(|\textbf{\tau}_{b}|\) [N\(\cdot\)m\({}^{-2}\)] at peak flow (i.e., \(t=3\) h) for the present-day soil use and management (simulation CN89-A). In agreement with the simulated flow velocities, the runoff exerts high stresses in the southern region to the Manillas stream because of the steep slopes. The values are more significant than the critical threshold \(\tau_{c}=0.083\) N\(\cdot\)m\({}^{-2}\)[77] for silt motion in most watersheds. The highest values occur in the headwater streams, \(|\mathbf{\tau}_{b}|\sim O(10^{2})\), decreasing progressively downstream and keeping high values of \(O(10)\) until the tributary streams reach the main Manillas stream. In the olive-grove region of the southern watershed, erosional processes are also dominant because the shear stress is above the critical value for erosion. The high shear stress and the fine granulometry of available sediments favour transport processes dominated by wash load. Slackwater sediments may settle in the inundated floodplains with a low flow velocity of the Manillas stream where \(|\mathbf{\tau}_{b}|<\tau_{c}\)[55]. The high spatial resolution of the numerical simulation allows the identification of multiple-scale geomorphological processes, see Figure 7, illustrating such sediment transport regimes. Figure 7: Examples of fluvial geomorphological features in the Manillas watershed that serve to verify the accuracy of the simulation CN89-A. (**a**) Gully network in the eastern headwater (red rectangle in Figure 6c): the left column shows a zoom of the shear-stress map, an orthophoto and the slope direction map for the DEM; the photo in the right-hand-side depicts an upstream view of the existing gullies. (**b**) Confined single-thread channel eroded in a rocky bed due to high shear stresses. (**c**) Paleostage indicators of flood levels and bedforms developing in unconfined flow on a floodplain.