## 4 Discussion
### Seasonal Pattern of Mangrove Dynamics  
Based on the resulting maps, it is apparent that the year 2016 marked the start of the positive mangrove expansion, which seen in Figure 10 and the time-lapse animation in the Supplementary Animation S1. There were two of the largest expansion areas in the Porong River mouth contributing 24% of the total mangrove area extracted inside the ROI as of November 2019 (Figure 12). It is highly likely that the mudflow diversion procedure has promoted mangrove belt expansion in Porong Estuary. Mud pumping disposal of LUSI discharged extra sediment supply thereby providing a suitable environment that enhanced mangrove expansion. Figure 11 provides detail of the significant increase of mangrove extent both on the ROI and focusing on the estuary. Dredging operation and the completion of LUSI Island construction in 2011 have contributed to the prominent increase of the mangrove area. The mangrove expansion followed a seasonal pattern as Figure 12 clearly indicates. We observed recession of the mangrove extent during the transition of dry to wet season and regrowth during the wet to dry season. The wet season has the highest sedimentation rates related to the mudflow pumping operation in LUSI. The mud is disposed of in the wet season and stored in the reservoir during the dry season. The seasonal pattern in Porong was also indicated in the study by [PERSON] et al. (2016) [21]. In principle, net development trend of the mangrove area is positive. Investigated further, we can see amplitude of the high-low signal differs in the period of 2013-2017 from that in 2018-2019. In 2013-2017, we can see low mangrove extent in the wet season followed by the high regrowth in the dry season. In contrast, from 2018 to 2019, we observe only a slight decrease in the wet season and a high roughly two-fold increase in the dry season. Focusing on the Porong river mouth, as shown in Figure 12b, the seasonal fluctuation is also recognised but is less pronounced as in Figure 12a. The graphs reveal continuous expansion until August 2013, irrespective of the region, thus no recession visible in both regions. From August to November 2013, there is a sudden recession, i.e., sharp decrease of area in region A and slightly less in region B. The recession took place in the middle of the dry season and the beginning of the wet season, thus at the end of the dry season. There is recovery occurring from November 2013 until August 2014, where recovery is more pronounced for region A (February and May clear satellite images are lacking in 2014). The recovery occurred during the wet to dry season. It seems that the recession occurred at the end of the dry season while recovering and return to expansion happens in the middle of the wet season and the first half of the dry season. This 2013 recession-recovery behaviour repeats in 2014-2017, where the fluctuation is noticeable in region A and less in region B. It is likely in the beginning mangroves start growing on the newly deposited, homogeneously distributed mud since its sediment attributes are rather suitable for their growth. Mangroves have access to water during wet season as well as during dry season. However, because of their existence, further sediment is deposited at the margin of the forest. This possibly transforms them into the basin mangrove type in certain areas, more so in the landward direction, less so on the delta lobes. When the trees start generative production, i.e., propagule production, at an age of three years seedling that are known to be more sensitive to salt and drought might die under the extreme conditions at the end of the dry season in the basins. This condition has developed from the interplay of vegetation and geomorphological processes--namely, the massive sediment load.