Live-bed failure modes of bendway weirs and rock vanes in alluvial channels

2022 Summer.Includes bibliographical references.Bendway weirs and rock vanes are instream rock structures primarily used for managing the alignment of a channel's thalweg. Built from rock, bendway weirs and rock vanes are intended to function by directing flow away from a channel's outer bank and thereby reducing flow velocity along the outer bank. The present study investigated how bendway weirs and rock vanes placed in curved, alluvial channels subject to live-bed flow conditions (active bed-sediment transport) may fail. Further, the experiments then sought to recommend design dimensions so that bendway weirs and rock vanes accommodate failure (and loss of rock), thereby enabling them to continue performing as intended. A curved flume was constructed in Colorado State University's Hydraulics Laboratory to conduct experiments that illuminated the failure modes and to confirm (or modify) preliminary design recommendations obtained from experiments using a straight flume fitted with three bendway weirs or rock vanes. The curved flume experiments involved a series of six bendway weirs or rock vanes and used a hydrograph procedure to simulate the rising limb of a hydrograph of flow along a medium sized river like the Middle Rio Grande; the proportions of the flume were like selected bends in that river. Six bendway weirs or rock vanes were needed to direct flow around the curved flume, as opposed to the need for three bendway weirs or rock vanes in the experiments in the straight flume. Two sizes of non-uniform bed sediment also were used (a medium sand and very coarse sand) for the experiments. The two sands were used to see if bed sediment size affected the failure modes. The experimental results showed that bendway weirs and rock vanes experienced rock dislodgement primarily via contraction scour, which undermines the end, or tip, of these instream structures. Destabilized rock then tumbles into the scour zone along the channel's shifted thalweg, armoring the bed. This observation was observed for both the beds comprised of medium sand and very coarse sand. As flow depth increased above the mean elevation of the bendway weirs or rock vanes, contraction of flow reduced as more flow passed over the structures. The flow field at each bendway weir or rock vane changed. The hydrograph procedure yielded similar changes in bed bathymetry for beds of medium sand and very coarse sand over the rising limb of the hydrograph. When (Δy+H)/H = 0.75, a deep scour hole formed in between the first two structures in the configuration within about 15 minutes. Then, when (Δy+H)/H = 1.25, the scour hole was partially filled with sediment and extended downstream largely along the series of bendway weirs or rock vanes. Further, when (Δy+H)/H = 2.0, the scour hole was again partially filled with sediment, but scour extended along the entire configuration of bendway weirs or rock vanes, thereby delineating a defined thalweg. As the flow depth increased, the maximum scour depth along the thalweg decreased for the experiments. The bendway weirs and rock vanes experienced structural deformation due to rock dislodgement primarily from contraction scour. Less rock dislodgement occurred for these instream structures placed on the medium sand than when on the very coarse sand. Also, the rock vanes experienced less rock dislodgement than did the bendway weirs in general. This finding is attributed to upwards slope of the crest of rock vanes; the sloped crest directed more flow around each rock vane and over the already armored bed. The results from using the hydrograph procedure in a curved flume confirmed the preliminary design recommendations from the straight flume. The design recommendations required that bendway weirs or rock vanes be lengthened by 2d100 and their crests be widened by d100; here d100 is the diameter of the largest rock used to build bendway weirs or rock vanes. This lengthening and widening accounts for the shortening and narrowing of bendway weirs or rock vanes subject to scour. A prior study recommended the size of rock chosen in design to form bendway weirs or rock vanes

Mindfulness-Based Art Therapy and Stress Reduction with Veterans Living in Transitional Housing

Veterans living in a transitional housing facility participated in an eight-week mindfulness-based art therapy group with the goal to reduce symptoms of depression, anxiety and stress, as well as increase mindful awareness and well-being. The results indicated that depression, anxiety and stress reduced over the course of the group and additionally, the veterans reported subjective experience of reduced symptoms and increased coping skills. Present moment awareness increased slightly. Art analysis indicates qualitative changes in the veteran’s self portraits including shifts in energy levels such as increased energy and shifts in mental health status. This research shows promising benefits for teaching veterans to manage symptoms of depression, anxiety, and stress by using art therapy and mindfulness

Theory of Picosecond-Laser-Induced Fluorescence from Highly Excited Complexes with Small Numbers of Chromophores

The problem of singlet excitation kinetics and dynamics, especially at high excitation intensities, among a small number of chromophores of a given system has been addressed. A specific scheme for the kinetics is suggested and applied to CPII, a small chlorophyll (Chl)a/b antenna complex the fluorescence lifetime of which has been reported to be independent of excitation intensity over a wide intensity range of picosecond pulses. We have modeled the kinetics from the point of view that Chla molecules in CPII are Förster coupled so that a second excitation received by the group of Chla's either creates a state with two localized excitons or raises the first one to a doubly excited state. The data on CPII can be understood on the basis of a kinetic model that does not exclude exciton annihilation during the excitation pulse. The implied annihilation rate is consistent with our theoretical estimates of that rate obtained by applying excitation transfer theory to pairs of molecules both initially excited