Transporte de sedimentos del Arroyo Napostá Grande, Bahía Blanca, provincia de Buenos Aires

hydraulic and sedimentological results of a field survey to the napostá grande creek are presented. the lower, highly meandering course flows through bahía blanca city. this part of the creek is greatly affected by hydraulic man-made features such as railways, car and walking bridges, canalisations, a structure that separates the extreme flood water, urban rainwater collection, cleaning, etc. in addition, sand is being extracted from the channel for construction. despite the remarkable influence that the stream has on the city, there are no quantitative records of the sediment transport within the stream. the objective of this work is to determine the liquid an solid flux over a section, evaluate the dynamic and turbulent characteristics of the flux, find a proper methodology suitable for this particular situation and define a formulation that predicts most accurately the bed load transport in the napostá creek. a proper cross-section after a recognition walk along several kilometres along the course of water has been done. as the stream shows several meanders it was difficult to locate an ideal cross section. the one chosen had some problems from the hydraulic point of view (partially symmetrical area, presence of a sand bar located in a rather short straight length), but on the other hand, the accessibility was excellent with available electric supply. bathymetry of the surrounding area was carried out and a map was produced with isobaths with 0.5 m equidistance. velocities at vertical profiles separated 0.5 m were obtained with a propeller along the cross-section and, based on these data, equal- velocity curves were drawn over the transversal section. these allowed the determination of the water flux and the bottom shear stress distribution along the cross section and wet perimeter. within the section, bedload sediment transport was sampled using helley-smith kind bedload traps, at various locations, confirming different transport rates at each point. traps gathe