Transport processes in the Santa Cruz Channel, Brazil

Abstract

The Santa Cruz Channel is part of the Itamaracá–Itapessoca estuarine system in Brazil’s Northeast region. It presents a complex geometry and receives the debouches of several small streams. Here we present an assessment of the hydrodynamics of the Santa Cruz Channel and its role on the suspended sediment transport. A field campaign was carried out when water level, cross-sectional flow, current velocity and direction, salinity, and turbidity were recorded during a complete semi-diurnal tidal cycle during the peak of the wet period when the freshwater and river-borne suspended sediment are highest. Longitudinal distribution of salinity and turbidity were also recorded along a transect starting at the adjacent sea up to the upper estuary (salinity = 0). Tides are the main driver of the transport processes, even considering that the observations were during the peak of the rainy season. The salinity displayed intra-tidal stratification, increasing to the low water and vanishing to the high water, which can be explained in terms of the tidal straining effect. So, the Santa Cruz channel behaves as a ‘Strained Induced Periodic Stratified’ (SIPS) system. The horizontal density gradient producing gravitational circulation seems to have a minor role in producing exchange flows. The suspended sediment input by the local river drainage dispersed along the systems displaying a conservative behavior. However, the hydrodynamic condition favors the retention of the river-borne sediment in the system, which has a high trapping efficiency.