PhD, Environmental Water Resources Engineering University of California, Berkeley Phone: 886-2-2369-2466 Address: Department of Bioenvironmental Systems Engineering National Taiwan University Taipei 106, Taiwan
Undular flows over riffles (standing waves with underlying open-channel flows) facilitate a quali... more Undular flows over riffles (standing waves with underlying open-channel flows) facilitate a quality environmental setting for riverine habitats. Understanding their link with hyporheic exchange flow (HEF) is important from eco-hydro-geomorphic perspectives. We conduct refractive index-matched scanning experiments to resolve the exchange between surface and subsurface flows across a coarse granular bed. We show that the HEF includes wave pumping (WP) and grain-scale pumping (GP) components. Mechanistically, the dynamic pressure gradient best explains the HEF on both wave and grain scales. However, due to the underlying open-channel flow, the result exhibits a phase lag compared to the theoretical WP, suggesting a necessary shift from the existing water surface-based model to a pressure gradient-based approach. Quantitatively, with the present experimental setting, the GP flux is 1 order of magnitude smaller than the WP flux. The relative significance of WP to GP is further increased at higher discharges, indicating potential utility of WP in habitat vitalization.
Gravel-bed clusters are the most prevalent microforms that affect local flows and sediment transp... more Gravel-bed clusters are the most prevalent microforms that affect local flows and sediment transport. A growing consensus is that the practice of cluster delineation should be based primarily on bed topography rather than grain sizes. Here we present a novel approach for cluster delineation using patch-scale high-resolution digital elevation models (DEMs). We use a geostatistical interpolation method, i.e., factorial kriging, to decompose the short-and long-range (grain-and microform-scale) DEMs. The required parameters are determined directly from the scales of the nested variograms. The short-range DEM exhibits a flat bed topography, yet individual grains are sharply outlined, making the short-range DEM a useful aid for grain segmentation. The long-range DEM exhibits a smoother topography than the original full DEM, yet groupings of particles emerge as small-scale bedforms, making the contour percentile levels of the long-range DEM a useful tool for cluster identification. Individual clusters are delineated using the segmented grains and identified clusters via a range of contour per-centile levels. Our results reveal that the density and total area of delineated clusters decrease with increasing contour percentile level, while the mean grain size of clusters and average size of anchor clast (i.e., the largest particle in a cluster) increase with the contour percentile level. These results support the interpretation that larger particles group as clusters and protrude higher above the bed than other smaller grains. A striking feature of the delineated clusters is that anchor clasts are invariably greater than the D90 of the grain sizes even though a threshold anchor size was not adopted herein. The average areal fractal dimensions (Hausdorff-Besicovich dimensions of the projected areas) of individual clusters, however, demonstrate that clusters delineated with different contour percentile levels exhibit similar planform morphologies. Comparisons with a compilation of existing field data show consistency with the cluster properties documented in a wide variety of settings. This study thus points toward a promising, alternative DEM-based approach to characterizing sediment structures in gravel-bed rivers.
The Physical Habitat Simulation System (PHABSIM) is modified herein to investigate the variation ... more The Physical Habitat Simulation System (PHABSIM) is modified herein to investigate the variation of substrate composition and instream habitat with flowrate. The revised PHABSIM includes a sub- program performing substrate analysis under five schemes. Sinogastromyzon puliensis in Chou-Shui Creek of Taiwan is selected for the case study. The results indicate that the weighted usable area (WUA) corresponding to the specified substrate attribute is the highest, whereas the WUA based on the original substrate is the lowest. The WUA values corresponding to the above-critical bed material and the armor are similar. The maximum bedload size scheme is based on the selective transport condition representing a more realistic ecohydraulic modeling of the instream physical habitat. ???????? The Physical Habitat Simulation System (PHABSIM) is modified herein to investigate the variation of substrate composition and instream habitat with flowrate. The revised PHABSIM includes a sub- program perfo...
Approximation techniques for estimating stochastic parameters of the non-homogeneous Poisson (NHP... more Approximation techniques for estimating stochastic parameters of the non-homogeneous Poisson (NHP) model are presented. The NHP model is characterized by a two-parameter cumulative probability distribution function (CDF) of sediment displacement. These two parameters are, respectively, the temporal and spatial intensity functions physically representing the inverse of average rest period and step length of sediment particles. The NHP model is mathematicall
ABSTRACT Sediment-maintenance flushing flows designed,to mimic,the action of natural floods in re... more ABSTRACT Sediment-maintenance flushing flows designed,to mimic,the action of natural floods in removing,the accumulated,fine sediments from the channel and loosening the gravel bed have been increasingly proposed,as an effective alternative in dam management and a required component of riverine restoration programmes. However, reservoir releases are generally associated with financial and environmental costs, thus it is highly desirable to specify flushing flows
First-order approximation techniques for estimating stochastic parameters of a sediment transport... more First-order approximation techniques for estimating stochastic parameters of a sediment transport model are presented. The non-homogeneous compound Poisson model of Shen-Todorovic eliminating certain idealized assumptions to describe the movement of sediment in natural streams is a revision of the earlier homogeneous model of Einstein-Hubbell-Sayre. However, the complexity of the non-homogeneous model and the difficulty in determining the model parameters has
In this work we incorporate the effect of near-bed coherent flow structures into the entrainment ... more In this work we incorporate the effect of near-bed coherent flow structures into the entrainment of randomly configured mixed-size sediments. The fourth-order Gram-Charlier type probability density function (GC pdf) of near-bed streamwise velocity is employed to account for the higher-order correlations associated with turbulent bursting. A compilation of the published data over a wide range of bed roughness is used
The deposition of the instantaneously released sediment into a gravel matrix and the hydraulic re... more The deposition of the instantaneously released sediment into a gravel matrix and the hydraulic resistance induced by the rapid siltation are investigated herein. The experimental results reveal that the depo- sitional patterns of the sediment are governed by the gravel-sediment size ratio, the amount of sediment released, and the seepage flowrate. The observations also indicate that the stable stage of
Page 1. 934 / JOURNAL OF HYDRAULIC ENGINEERING / SEPTEMBER 1999 VARIATION OF ROUGHNESS COEFFICIEN... more Page 1. 934 / JOURNAL OF HYDRAULIC ENGINEERING / SEPTEMBER 1999 VARIATION OF ROUGHNESS COEFFICIENTS FOR UNSUBMERGED AND SUBMERGED VEGETATION By Fu-Chun Wu,1 Hsieh Wen Shen,2 Member, ASCE, and Yi-Ju Chou3 ...
Undular flows over riffles (standing waves with underlying open-channel flows) facilitate a quali... more Undular flows over riffles (standing waves with underlying open-channel flows) facilitate a quality environmental setting for riverine habitats. Understanding their link with hyporheic exchange flow (HEF) is important from eco-hydro-geomorphic perspectives. We conduct refractive index-matched scanning experiments to resolve the exchange between surface and subsurface flows across a coarse granular bed. We show that the HEF includes wave pumping (WP) and grain-scale pumping (GP) components. Mechanistically, the dynamic pressure gradient best explains the HEF on both wave and grain scales. However, due to the underlying open-channel flow, the result exhibits a phase lag compared to the theoretical WP, suggesting a necessary shift from the existing water surface-based model to a pressure gradient-based approach. Quantitatively, with the present experimental setting, the GP flux is 1 order of magnitude smaller than the WP flux. The relative significance of WP to GP is further increased at higher discharges, indicating potential utility of WP in habitat vitalization.
Gravel-bed clusters are the most prevalent microforms that affect local flows and sediment transp... more Gravel-bed clusters are the most prevalent microforms that affect local flows and sediment transport. A growing consensus is that the practice of cluster delineation should be based primarily on bed topography rather than grain sizes. Here we present a novel approach for cluster delineation using patch-scale high-resolution digital elevation models (DEMs). We use a geostatistical interpolation method, i.e., factorial kriging, to decompose the short-and long-range (grain-and microform-scale) DEMs. The required parameters are determined directly from the scales of the nested variograms. The short-range DEM exhibits a flat bed topography, yet individual grains are sharply outlined, making the short-range DEM a useful aid for grain segmentation. The long-range DEM exhibits a smoother topography than the original full DEM, yet groupings of particles emerge as small-scale bedforms, making the contour percentile levels of the long-range DEM a useful tool for cluster identification. Individual clusters are delineated using the segmented grains and identified clusters via a range of contour per-centile levels. Our results reveal that the density and total area of delineated clusters decrease with increasing contour percentile level, while the mean grain size of clusters and average size of anchor clast (i.e., the largest particle in a cluster) increase with the contour percentile level. These results support the interpretation that larger particles group as clusters and protrude higher above the bed than other smaller grains. A striking feature of the delineated clusters is that anchor clasts are invariably greater than the D90 of the grain sizes even though a threshold anchor size was not adopted herein. The average areal fractal dimensions (Hausdorff-Besicovich dimensions of the projected areas) of individual clusters, however, demonstrate that clusters delineated with different contour percentile levels exhibit similar planform morphologies. Comparisons with a compilation of existing field data show consistency with the cluster properties documented in a wide variety of settings. This study thus points toward a promising, alternative DEM-based approach to characterizing sediment structures in gravel-bed rivers.
The Physical Habitat Simulation System (PHABSIM) is modified herein to investigate the variation ... more The Physical Habitat Simulation System (PHABSIM) is modified herein to investigate the variation of substrate composition and instream habitat with flowrate. The revised PHABSIM includes a sub- program performing substrate analysis under five schemes. Sinogastromyzon puliensis in Chou-Shui Creek of Taiwan is selected for the case study. The results indicate that the weighted usable area (WUA) corresponding to the specified substrate attribute is the highest, whereas the WUA based on the original substrate is the lowest. The WUA values corresponding to the above-critical bed material and the armor are similar. The maximum bedload size scheme is based on the selective transport condition representing a more realistic ecohydraulic modeling of the instream physical habitat. ???????? The Physical Habitat Simulation System (PHABSIM) is modified herein to investigate the variation of substrate composition and instream habitat with flowrate. The revised PHABSIM includes a sub- program perfo...
Approximation techniques for estimating stochastic parameters of the non-homogeneous Poisson (NHP... more Approximation techniques for estimating stochastic parameters of the non-homogeneous Poisson (NHP) model are presented. The NHP model is characterized by a two-parameter cumulative probability distribution function (CDF) of sediment displacement. These two parameters are, respectively, the temporal and spatial intensity functions physically representing the inverse of average rest period and step length of sediment particles. The NHP model is mathematicall
ABSTRACT Sediment-maintenance flushing flows designed,to mimic,the action of natural floods in re... more ABSTRACT Sediment-maintenance flushing flows designed,to mimic,the action of natural floods in removing,the accumulated,fine sediments from the channel and loosening the gravel bed have been increasingly proposed,as an effective alternative in dam management and a required component of riverine restoration programmes. However, reservoir releases are generally associated with financial and environmental costs, thus it is highly desirable to specify flushing flows
First-order approximation techniques for estimating stochastic parameters of a sediment transport... more First-order approximation techniques for estimating stochastic parameters of a sediment transport model are presented. The non-homogeneous compound Poisson model of Shen-Todorovic eliminating certain idealized assumptions to describe the movement of sediment in natural streams is a revision of the earlier homogeneous model of Einstein-Hubbell-Sayre. However, the complexity of the non-homogeneous model and the difficulty in determining the model parameters has
In this work we incorporate the effect of near-bed coherent flow structures into the entrainment ... more In this work we incorporate the effect of near-bed coherent flow structures into the entrainment of randomly configured mixed-size sediments. The fourth-order Gram-Charlier type probability density function (GC pdf) of near-bed streamwise velocity is employed to account for the higher-order correlations associated with turbulent bursting. A compilation of the published data over a wide range of bed roughness is used
The deposition of the instantaneously released sediment into a gravel matrix and the hydraulic re... more The deposition of the instantaneously released sediment into a gravel matrix and the hydraulic resistance induced by the rapid siltation are investigated herein. The experimental results reveal that the depo- sitional patterns of the sediment are governed by the gravel-sediment size ratio, the amount of sediment released, and the seepage flowrate. The observations also indicate that the stable stage of
Page 1. 934 / JOURNAL OF HYDRAULIC ENGINEERING / SEPTEMBER 1999 VARIATION OF ROUGHNESS COEFFICIEN... more Page 1. 934 / JOURNAL OF HYDRAULIC ENGINEERING / SEPTEMBER 1999 VARIATION OF ROUGHNESS COEFFICIENTS FOR UNSUBMERGED AND SUBMERGED VEGETATION By Fu-Chun Wu,1 Hsieh Wen Shen,2 Member, ASCE, and Yi-Ju Chou3 ...
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