## 4 Discussion and Possible Study Limitations  
The results of the model allowed for a comparison of the NbS using the changes observed in runoff and peak discharge. All NbS combinations were associated with a decrease in runoff volume, along with a decrease in peak discharge. Multiple scenarios also showed a delay in the peak discharge. These results from the model suggest that the proposed NbS could be an effective way of mitigating the issues with runoff management in the study area. When comparing the three solutions implemented in the east sub-catchment separately, Scenario 2 (permeable parking) presents the best results in terms of percent change in runoff volume. It presents the highest runoff reduction in Scenarios 1-3 in 9 out of the 10 simulations. This trend is also reflected in the effect on peak discharge. In all events, the use of permeable parking is more effective in reducing peak discharge compared to the other two solutions. In this case study, the parking area represents the largest single impervious area. Restoring permeability thus leads to the largest reduction in runoff and peak discharge of the modelled solutions. This finding is important because it indicates that this specific solution could be effective in similar contexts, where a small catchment has a significant area of permeability and shares specific characteristics of the terrain and the storm event. In this case, permeable parking is shown as most effective in flood mitigation. The ponds reduced the peak discharge significantly in most cases and therefore helped overall performance when combined with the other NbS. Scenario 6 was the best performing scenario overall. The behaviour of the ponds and their impact on peak discharge changed between events and showed little correlation with the characteristics of each precipitation event. The ponds demonstrated a slight increase in lag time in most events due to water being stored in the ponds. The delay in discharge peak was between 0 and 40 min across the rainfall events compared to the \"No solutions\" scenario. In addition to delaying the peak, the ponds delayed the rising limb of the hydrographs and reduced the reactivity of the basin to precipitation. The hydrograph from Event 9 (Figure 5) showed a smoother discharge curve as a result of water storage from pond implementation. The results of this study align with a previous work showing that ponds help reduce the peak discharge, smoothing and distributing floods over time and providing more time for infiltration [73]. Scenarios 4 and 6 with all NbS implemented had the highest runoff % reduction for all simulations, and Scenario 6 performed best in reducing peak discharge. These findings emphasise the importance of implementing multiple solutions. This supports other literature works on nature-based solution analysis [2; 70; 74] and the \"sponge-city\" concept [20; 75]. Notable changes in runoff were observed when changing the impervious % parameter across the scenarios, especially in Scenario 3, where green roofs were modelled only by altering this parameter and not the CN. This highlighted the importance of this parameter in HEC-HMS models, as well as the overall significance of impervious surfaces in runoff processes. The results reaffirm the choice of NbS over grey infrastructure due to the reduction in impervious area, one of the main benefits associated with NbS. As well as the changes in runoff and peak discharge, the NbS used in this study have differing levels of ecological benefits. Permeable paving does not contribute much to habitat provision compared to green roofs and ponds [76]; therefore, although it is most effective in reducing runoff, it is not recommended as an independent solution due to the study area being part of a natural heritage site. In very high rainfall events like Events 3, 4 and 10, the capacity of the implemented solutions to mitigate runoff volume may be overwhelmed, resulting in a lower reduction in runoff volume.