## 4 Discussion  
### Topographic Control of Hortonian and Dunnian Flow  
Surface runoff, also known as Hortonian runoff due to infiltration excess or simply Hortonian flow, refers to the hydrological process that occurs when precipitation intensity exceeds the soil's infiltration capacity, generating surface runoff [15, 53]. This type of flow was first described by [PERSON] in 1933 and primarily occurs in soils with low permeability or that are already compacted, where rainwater cannot infiltrate quickly, leading to surface runoff. On the other hand, Dunnian flow, also known as saturation overland flow, occurs when the soil is fully saturated with water, meaning its infiltration capacity has been exceeded. This type of runoff typically begins in low-lying areas, such as riparian zones, where the water table is near the surface [17]. Dunnian flow is characteristic of regions with high precipitation and permeable soils, predominating in forested areas and slopes. Unlike Hortonian flow, it does not depend on rainfall intensity but rather on soil saturation, playing a significant role in groundwater recharge and the maintenance of watercourses [16, 17], as well as in soil hydraulic conductivity. According to [54], the amount of water infiltrating the soil influences the speed of surface runoff, as well as other hydrological variables. Therefore, we can expect that this perimeter of moist soil is associated with watercourses, such as floodplains and the major and minor channels of riverbeds. Based on this premise, we expected that the regions around the floodplain would have the highest NDWI values. However, this was not observed in the analysis of the longitudinal profile of the main river channel studied. According to [44], soil moisture of around 0.2 and even confusion between water and moist soil of around 0.35 were expected. However, analyzing the box plot and cumulative frequency diagram, we noticed that values above 0.2 are beyond the third quartile (Figure 8A). When we analyzed the moist perimeter, it was identified that it represents less than 20% of the cumulative frequency of NDWI (Figure 8B). Figure 7: The soil moisture index proposed by [43]. We highlight that savanna areas 1 (west) and mining areas 2 (south) have the lowest indices. Areas 3 (north) and 4 (river mouth) show the highest indices, with area 3 having higher slopes and forest fragments, indicating the complex relationship between the Atlantic Forest, soil moisture, and hydrology in this basin. Diffusive flow, according to [55], emphasizes groundwater movement driven by piezometric pressure. Experimental studies have shown that flatter areas near watercourses are more susceptible to rapid saturation [55]. However, considering that the water deficit (Figure 9) for the image acquisition period was 4.7%, it was expected that a higher accumulation of soil moisture would be found. We attribute these low NDWI values to the removal of riparian vegetation and high evapotranspiration typical of a region located at just 12\({}^{\circ}\) south latitude. At the hilltops of the geomorphological slope, as described by [56], soils are characterized by shallow depth and predominant chemical weathering, leading to slope instability. Remnants of Atlantic Forest act as soil stabilizers, delaying Dunnian flow. In contrast, the studied basin features deep soils with good drainage [57], which favor infiltration rather than subsurface flow. Therefore, the forest plays a crucial role in retaining soil moisture and supporting subsurface flow for longer periods. This can be observed in a cross-sectional cut at the top of the slope (Figure 10), where the blue line represents NDWI and the green line represents NDVI. Regions characterized by significant remnants of Atlantic Forest show high NDVI values, where NDWI values expectedly hover close to zero or even negative, as noted by [44; 58], where values above 0.2 indicate soil moisture presence.