Author(s): Alexander N. Sukhodolov; Wim S. J. Uijttewaal; Schnauder; Tatiana A.; Sukhodolova; Christiaan Erdbrink; Wernher Brevis; Xavier-Francois Garcia; Martin Pusch; Friederike Gabel
Keywords: Turbulence; Macrophytes; Mixing layers; Invertebrates; Bedforms
Abstract: In the recent years flow visualization, a valuable method in experimental studies, gained a new prospective for studies of flow structure in natural streams. Complimentary to conventional particle tracking (PTV) and image velocimetry (PIV), visual observation of flow domain in natural streams with artificial (seeded particles) or natural (aquatic plants, invertebrates) tracers has particularly important implications for environmental fluid mechanics and ecohydraulics. Though the visualization methods developed in experimental fluid mechanics are already greatly advanced, their application to natural streams is difficult or even impossible. Available reports on field studies provide little information on theoretical grounds of methodologies they used and often lack a direct comparison of obtained results with conventional point measuring techniques. The aim of this paper is to summarize experience gained from recent applications of visual techniques for studies of shallow mixing layers, flow over submerged aquatic plants, and to outline perspectives for further application in ecohydraulics and studies of transport processes in rivers. The methodological aspects of PTV application in natural environments are discussed and comparison with results of point velocity measurements is presented for semi-controlled field experiments. Synchronous video records of vegetation canopy and instantaneous flow velocity vectors are shown to provide valuable information on coherent structures of the flow and their interaction with canopies. Perspectives of coupling visual methods and techniques with point velocimetry for studies of complex flow-biota interactions are discussed on examples of resent investigations of invertebrates’ entrainment into drift under action of waves.