Tide propagation in tidal courses of the Pará river estuary, Amazon Coast, Brazil

On the Para River (estuary) there are approximately one hundred tidal channels. These channels are important systems in both ecological and socio-economic systems. This paper aims to determine the tidal propagation pattern in the tidal channels in the dry and rainy seasons. Three tidal channels were selected on the left margin (Marajo Island). In a first experiment, two pressure sensors were installed in each channel for 13 hours during a spring tide, one in the mouth and the other approximately 3 km upstream. In a second experiment, 3 pressure sensors were installed in one of the channels (36 days): one outside the channel (Para river), one in the mouth and another one upstream in the channel. The first experiment revealed that the channels have similar pattern and asymmetric tidal regime, whose flood takes approximately 4 h and the ebb, 8 hours. The absence of an effective river discharge may favour the flood. The presence of sandy banks in the mouth of these channels trap the water inside, which makes the ebb last longer. In the second experiment, harmonic tidal constituents were obtained at the outside point. In the channel and channel mouth there was no variation in the low tidal level during the dry season, possibly due to morphology effects. In the rainy season there was slight variation in low tide level and this was more evident on the spring tide.