Influence of dead-water zones on the dispersive mass transport in rivers

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The study investigates dispersive mass transport in rivers to enhance predictability during accidental pollutant spills, focusing on the impact of dead-water zones created by groin fields on transport characteristics. A literature review of detailed maps from the Rhine, Waal, and Elbe rivers informed the design of representative laboratory experiments. Key parameters, including typical aspect ratios and inclination angles of groin fields, were summarized. Laboratory flume experiments utilized schematized groins, varying aspect ratios, inclination angles, and groin field volumes. Given the shallow, quasi two-dimensional flow, surface velocities were measured using a specialized Surface Particle-Image-Velocimetry-System. Additional velocity distribution measurements were conducted with a two-dimensional Laser-Doppler-Velocimeter. These methods revealed typical recirculating flows in groin fields and coherent horizontal eddies in the mixing layer, which govern mass exchange. High-resolution surface PIV measurements enabled estimation of mass exchange between groin fields and the main stream, showing that mass exchange increases with groin field length. A tracer injection device was developed for producing homogeneous concentration fields. Lastly, a Lagrangian-Particle-Tracking-Method was created to relate local results from groin fields to overall transport characteristics in pollutant spill scenarios, allowing for parameterizati