ABSTRACT
This research is focused on determining the incipient motion of a sediment bed of five rivers in the Terraba River catchment in Costa Rica. Gravel to boulder particles in sediment bar were monitored in order to determine which diagram of initiation of motion better describes this type of river. The grain size of the sediment analyzed has a D50 from 15.5 mm to 132.3 mm and the study period was the rainy season of 2014. The incipient motion was identified directly on the superficial layer of the sediment bar. The critical shear stress for sediment movement was determined with a calibrated numerical model. Finally, it is suggested that the Modified Shields Diagram (Parker 2005) can be used to evaluate the incipient motion of bed load sediments in the rivers of Costa Rica.
