## 3 Results
### Sao Jacinto Sea Outfall's Plume Monitoring through High-Spatial Resolution True Color Product  
The average catchment area for the study period was approximately 1.80 km\({}^{2}\) with a standard deviation of 3.41. The greatest areas were found in the second half of 2017, where it reached the largest catchment area, 19.12 km\({}^{2}\), on 24 December 2017. In order to detect unusual patterns in the dataset, the seasonal tendency was removed, although there was no strong tendency identified (see Supplementary Materials) by calculating the anomaly from each area of each image against the average of the month that image was captured; the result is shown in Figure 8. The \"0\" in the figure was established as the mean value calculated for the total period. For this, the inter-annual monthly average area was calculated, summed, and divided by 12 (months of the year). Finally, the bars represent the result of removing the monthly average value from each daily sea outfall plume area. October 2017 was found to be the most continuous period of the sea outfall's plume visibility. Thus, to exemplify the ability to monitor the Sao Jacinto sea outfall turbid plume dispersion with true color imagery, the images from this period are addressed.  
Figure 6: Seasonal Sao Jacinto sea outfall plume visibility.  
Figure 8: São Jacinto sea outfall turbid plume area anomaly throughout the four years of study. The anomaly was calculated by subtracting the monthly sea outfall average area from the daily sea outfall area of the respective month.  
Figure 7: Annual plume catchment area for the respective period of analysis.  
In total, for the aforementioned month, 11 images were available, and the turbid plume was observed propagating towards the Barra inlet channel, which means that the wastewater components could be entering the Aveiro lagoon. Hence, to understand the wastewater plume's dispersion during this period, the sea surface elevation, wind magnitude, and wind direction were also considered. Figure 9 shows the observed tidal condition and the wind magnitude and direction, the main forces that influence the coastal hydrodynamic.  
Following the hydrographic characterization, the ocean color images are displayed in Figure 10. The aforementioned conditions are visible in E, B, and F, respectively. Furthermore, during low tide (C, D, H, I, and J), the Aveiro lagoon plume acted as a superficial barrier for the wastewater's plume dispersion, which can be seen in particular in C and J. The flood tide (A, B, E, F, G, and K) drove the pollutant plume towards the coastal lagoon, detectable in B and E. Nonetheless, D was the only exception, with the wastewater discharge not being detected by the true color images.  
The tidal phases, ebbing and flooding, were able to restrict or induce the pollutant plume dispersion towards the Barra inlet channel, respectively. The Ria de Aveiro coastal lagoon runoff during low tide seemed to have acted as a superficial barrier for the turbid plume's diffusion. Additionally, the wind conditions also influence the plume's dispersion; however, its effect takes time to change the current's direction. In this sense, the continu  
Figure 9: (**A**) Sea surface elevation and (**B**) wind speed and direction for October 2017. The dashed lines represent the days when ocean color data are available, and the dots represent the precise water level at the time of the satellite passage. The dashed line and letters correspond to the moment of the tidal wave and wind condition when Sentinel-2 (S2) passed over the region, resulting in a total of 11 images (A to K).  
Figure 10: Sentinel-2 true color imagery for October 2017. Each image had its RGB bands manipulated in order to achieve the best turbid plume visualization. The yellow pin on the images corresponds to the São Jacinto sea outfall’s mouth. All the images have a spatial resolution of 10 m. The dark patch near the pin represents the sewage discharge onto the sea.