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This paper presents basic tests to develop an airborne photogrammetric methodology that derives grain size characteristics of gravel bed rivers. The data acquisition was done using a lightweight action cam and a hand-held digital single lens reflex camera. Image processing comprised the structure from motion technique and multiview-stereo algorithms to obtain digital elevation models of non-cohesive gravel beds. Laboratory results indicate that the method accuracy is about four to six times lower than laser-scan data when based on action cam data. The accuracy of digital elevation models computed via photos taken by the reflex camera is almost of the same range as the laser data. Field experiments were done to test the performance of image based gravelometry against manual surface sampling. For this application the action cam was mounted to a low-cost quadrocopter, while the reflex camera was operated by hand. Results indicate that this combination has a high potential to generate data from which characteristic grain size parameters can be estimated. [ABSTRACT FROM AUTHOR]

In this study the effects of the different rough porous beds in an open inclined channel are studied experimentally for impermeable and permeable porous bed. For the simulation of porous bed two different types of permeable bed with the same thickness ( s ′=3 cm) and the same porosity ε =0.70 are used: (a) porous filters and (b) gravel bed. Laboratory experiments were used for the calculation of turbulent velocity profiles. Measurements of velocity were taken for inclined channel for three different slopes ( S =−0.002, S =−0.004 and S =−0.006) and for five different flow depths ( h =5 cm, 7 cm, 9 cm, 11 cm and 13 cm). The total discharge Q varies from 0.78 to 1.31 l/s. The measurements were obtained using a two-dimensional (2D) Particle Image Velocimetry (PIV). The total discharge was estimated using a calibrated venture apparatus. Results showed that the presence of rough porous bed in inclined open channels influence significantly the turbulent characteristics of the flow in comparison with impermeable open channels with the same slopes. [ABSTRACT FROM AUTHOR]

Laboratory experiments of depth-limited open-channel flows over a gravel bed were conducted in the study. Two gravel patches with identical individual element size and different lengths (3.81 m and 7.5 m) were tested. The depth-limited uniform flow regime with relative submergence S r (= D / k s ) ranging from 2.68 to 5.94 was produced by adjusting the tailgate weir. The velocity profiles were measured by using both an ultra-sound velocity profiler (UVP) and an acoustic Doppler velocimeter (ADV). The conventional methods used to determine the zero-plane displacement and estimate the bed shear velocity were then reviewed and compared. The measured double-averaged (DA) velocity profiles were found to fit well with the log law and defect law with a non-universal Karman constant κ. κ -value remains nearly constant and in the range from 0.2 to 0.3 for the long patch (LP) cases and κ -values are scattered within a wider range from 0.3 to 0.5 for the short patch (SP) cases. While the Br -value in log law remains constant and equal to 8.5 for LP cases, the Br -value was found to decrease with the increase of the dimensionless roughness height k s + for SP cases. The streamwise turbulence intensity distributions were found to be independent on the patch length and agree well with the available experimental data in the intermediate region and wall region. The Manning resistance coefficient and Darcy–Weisbach friction factor were analyzed. The κ -value decreases to 0.22 for the fitting of the logarithmic flow resistance law under small relative submergence. The value of the integration constant Ar in the logarithmic law falls within the normal range between 3.25 and 6.25. [ABSTRACT FROM AUTHOR]

Abstract: Particle-Image-Velocimetry (PIV) has been applied to many different environmental flows in the last twelve years at the Institute for Hydromechanics, Karlsruhe Institute of Technology. The present paper gives an overview about the most important results gained with PIV during this period and summarizes the advantages and disadvantages of this measurement technique. PIV applications to determine velocities at the water surface as well as internal flows characteristics are discussed with respect to physical and technical aspects. It can be concluded that PIV is still not a standard tool, every application needs adaptation and comprises certain limitations. Every element of the measurement system (window size, camera, spatial and temporal resolution, etc.) has to fit exactly the physical problem to be examined. [Copyright &y& Elsevier]

Abstract: This paper presents the results of a laboratory flume experimental study on the interaction of bank vegetation and gravel bed on the flow velocity (primarily on the location of the maximum velocity, Umax ) and the Reynolds stress distributions. The results reveal that the dip of the maximum velocity below the water surface is up to 35% of flow depth and the difference between Umax and the velocity at the water surface is considerable in the presence of vegetation on the walls. The zone of the log-law varies from y/h=2 up to 15 percent of flow depth and it does not depend on distance from the wall. Deviation of the velocity profile in the outer layer over a gravel bed with vegetation cover on the walls is much larger than the case of flow over a gravel bed without vegetation cover on the walls. The presence of vegetation on the walls changes uniform flow to non-uniform flow. This fact can be explained by considering the nonlinear Reynolds stress distribution and location of maximum velocity in each profile at different distances across the flume. The Reynolds stress distributions at the distance 0.02 m from the wall have negative values and away from the wall, they change the sign taking positive values with specific convex form with apex in higher location. Average of von Karman constant κ for this study is equal to 0.16. Based on κ=0.16, the methods of Clauser and the Reynolds stress are compatible for determination of shear velocity. [Copyright &y& Elsevier]

Abstract: This paper reports on a numerical study of the drag moments exerted on bed gravels and the effect of near-bed coherent structures on the moments in turbulent open-channel flow. We employ the result of a numerical direct simulation (DNS) for the calculation. The particles are represented as a hexagonal arrangement of spheres and the depth of the flow is four times their diameter. The drag moments experienced by the spheres are calculated in two directions: streamwise (M D1) and spanwise (M D2). M D2 was found to be an important component for the horizontal moment, which is traditionally considered to be neglected. The majority of M D2 originates from pressure whilst the viscous force is as important as pressure for M D1. Further, the contributions of the forces from different vertical regions of the sphere to effective rotational moment are investigated. The quasi-streamwise vortices and the high-speed fluid between the vortices are strongly associated with M D2. The horizontal, rather than vertical, fluctuating velocities of both ejections and sweeps are shown to obviously affect M D1. [Copyright &y& Elsevier]

The Missouri Gravel Bed (MGB) is a system that uses pea gravel with 10% sand (v/v) as a root growth medium, allowing plants to be removed from the gravel and planted, bare root, during the growing season. However, the low water holding capacity of the medium necessitates frequent irrigation. This study was conducted to determine the effects of amending pea gravel with calcined clay (Terra-Green®) on the physical properties of the medium and on growth of Gymnocladus dioicus (L.) K. Koch seedlings. Adding 10% sand (v/v) increased water holding capacity of the medium slightly at water tensions above 1 kPa. Gravel amended with 40% calcined clay had 16% air-filled porosity and had 3.5 times more plant available water than gravel with sand only. Dry weights of seedlings grown in gravel amended with 40% calcined clay and no sand were over twice as great as those of seedlings grown in the standard MGB medium. [ABSTRACT FROM AUTHOR]