FIGURE 3
With respect to water balance during the dry season, most of the flow into Araguari River is blocked by the silting up of its former mouth, follows through Urucurituba Channel and flows into Bailique archipelago, in the Amazon River mouth. A second fraction of the flow - accumulated in Igarapé Tabaco region - returns to URU1 during ebb (Figure 4A), whereas during flood, it flows towards the old mouth and tends to spread to the lake regions through an affluent (Igarapé Tabaco). This flow leads to significant changes in water quality, such as salinization processes (Cunha and Sternberg, 2018). A third fraction of it (220 m3s-1), which represents the difference in flow between URU1 and URU2 stations, is diverted into the floodplain (complex network of channels and branches in the floodplain). Thus, the right bank of Urucurituba Channel is connected to Gurijuba-Igarapé Novo Channel and, again, to Araguari River (Figures 1 and 4A) – it receives water inflow during the high tide.
Most water flowing into Urucurituba Channel (URU1) during the rainy season comes from Araguari River. A second fraction of the flow heads towards Igarapé Tabaco region and returns to URU1 during ebb, and it indicates prevalence of fluvial discharge (ebb tide) in water balance. Finally, a third fraction of the water flow, which was estimated at 523 m3s-1 (Figure 4B), comes from the floodplain into Urucurituba Channel.
Thus, Urucurituba Channel, in URU1, assumingly captures 100% of Araguari River flow during the dry season, loses 29% of this total because it gets retained in the floodplain and dumps 71% of Araguari discharge into the Amazon River (URU2 = 548 m3s-1) (Figure 4A). On the other hand, URU1 receives 86% of direct flow coming from Araguari River anad absorbs additional 14% coming from the floodplain during the rainy season. It totals 100% of the discharge coming from Araguari River flowing into the Amazon River (URU2 = 3,688 m3s-1) (Figure 4B).