The interaction between vegetation, sediment, and water flow creates various fluvial landscapes. Hydrological conditions and flood disturbances, as well as the habitat preference of vegetation, regulate its spatial distribution. To describe the spatial distribution of vegetation cover, here, we focus on vegetation distributions along river transverse transects that define vertical and horizontal distances from water areas during low flow periods. As one of the most dynamic river types, braided rivers can be significantly influenced by vegetation encroachment. However, the effects of vegetation distributions along river transects on braided river morphology remain unknown. To study the potential influence of vegetation distribution along river transects, a depth-averaged, hydro-morphodynamic model was employed. Using the model, we investigated a medium-sized, braided river with a gravel bed affected by riparian vegetation. The following scenarios of vegetation transect distributions were examined: (1) vegetation established near or covering the low water channel, and (2) vegetation established on bar tops and kept at a distance from the low water channel. The model successfully reproduced a reduction in the braiding index for a vegetated braided river. Depending on the transect distribution scenarios employed, significantly different effects for river morphology were obtained. For example, compared to vegetation on bar tops, vegetation located near the low water channel played a more critical role for changing river morphology, redirecting water flow, and changing the statistical characteristics of the riverbed elevation distribution. Vegetation near the low water channel not only concentrated water flow to low water channels but also redirected flow to the high elevation area by reducing low water channel flow capacity. The revealed effects of the vegetation transect distribution on river morphology development helped to determine effective management protocols for reducing the negative impact of vegetation encroachment.
Bio-hydro-morphodynamic simulation is an essential tool for analyzing fluvial processes under the influence of riparian vegetation, and has developed over the past decade. However, most bio-hydro-morphodynamic models have neglected the flexibility of vegetation. The flow-induced deformation of flexible vegetation changes the resistance to water flow. Therefore, flexibility affects water flow surrounding vegetation patches, and alters bed shear stress below and surrounding patches. To investigate the effects of vegetation flexibility in a fluvial, bio-hydro-morphodynamic
Image-based stream flow observation consists of three components: (i) image acquisition, (ii) ortho-rectification, and (iii) an image-based velocity estimation. Ortho-rectification is a type of coordinate transformation. When ortho-rectifying a raster image, pixel interpolation is needed and causes the degradation of image resolution, especially in areas located far from the camera and in the direction parallel to the viewing angle. When measuring the water surface flow of rivers with a wide channel width, reduced and distorted image resolution limits the applicability of image-based flow observations using terrestrial image acquisition. Here, we propose a new approach for ortho-rectification using an optical system. We employed an optical system embedded in an ultra-short throw projector. In the proposed approach, ortho-rectified images were obtained during the image acquisition phase, and the image resolution of recorded images was almost uniform in terms of physical coordinates. By conducting field measurements, characteristics of the proposed approach were validated and compared to a conventional approach.
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