Turbulence and turbulent transport in sediment-laden open-channel flows

Some aspects of turbulence in sediment-laden open-channel flows are examined. A conceptual model based on similarity hypotheses rather than the traditional mixing-length closures is proposed. It is argued that, over a wide range of laboratory conditions, the main effect of the suspended sediment on the flow is confined to a layer near the bed. If such a distinct layer can be discerned, then this is separated from the outer flow by an inertial subregion in which the mean-velocity profile is approximately logarithmic, with an associated von Kàrman constant of ≈ 0.4, i.e., the same value as in single-phase flows. It is further shown that power-law profiles may be derived from general similarity arguments and asymptotic matching. These implications contrast with those of previous models in which changes in the mean-velocity profile are supposed to occur throughout the flow or primarily in the flow far from the bed. Length and concentration scales appropriate to sediment-laden flows are suggested. An experimental study was also undertaken. Both the saturated case, in which a sand bed was present, and the unsaturated case, in which a sand bed was absent, were investigated. The study was restricted to nominally flat beds, composed of three well sorted sands (median grain diameters ranged from 0.15 mm to 0.24 mm). A two-component laser-Doppler-velocimetry system was used for velocity measurements. Suction sampling was used to measure local mean concentrations. The major points of the conceptual model are supported by the experimental results. Higher-order statistics of the velocity field were found to exhibit little evidence of any effect on the outer flow, supporting the view that the effect of the suspended sediment is felt primarily in the inner region. This contrasts with the predictions of recent models that propose an analogy between sediment-laden flows and weakly stable density-stratified flows

What magnetic resonance imaging has told us about the pathogenesis of rheumatoid arthritis – the first 50 years

Modern imaging modalities, including magnetic resonance imaging (MRI), are valuable diagnostic and therapy monitoring tools in rheumatoid arthritis (RA). This article reviewed how these imaging modalities have greatly improved our understanding of pathogenic mechanisms in RA, namely the link between inflammation and damage. For example, traditional paradigms regarding the mechanisms of joint destruction, including the idea that synovitis and damage are uncoupled, have been challenged. As the power of MRI increases, there is a need to define normality since apparently normal joints occasionally exhibit MRI evidence of synovitis in the absence of symptoms

Ecologically Aware Design of Waterway-Encapsulating Structures

Aquatic organism passage (AOP) in waterways-encapsulating structures, particularly culverts, is of growing concern to environmental regulatory agencies, and the Indiana Department of Transportation (INDOT) is seeking systematic responses to this concern in the hydraulic design of such structures. This study reviews design approaches to enhance or accommodate aquatic organism passage through culverts, and proposes a simplified design procedure that requires less data input and analysis, and yet results in a structure complying with the current regional general permit (RGP) conditions. It also makes as much use of already existing INDOT standard specifications for riprap and coarse aggregates that would be as backfill material to form a stable bed within the culvert. The simplified procedure is intended for new larger structures for which a culvert bed needs to be installed, and for expected Indiana conditions of low-gradient ( Because of their larger size compared to traditional culverts, AOP-designed structures are associated with higher installation and material costs, which may however be compensated partially or wholly by lower costs over their operational lifetime. Previous work on life-cycle cost (including social/ecological costs) analysis of AOP-designed culverts was reviewed, but it is concluded that reliable data and methodologies for an adequate analysis are not yet available. The study then explores the consequences of alternative regulatory schemes formulated on the basis of habitat or biotic integrity indices. These may permit simple yet more flexible schemes with the same or even better ecological outcomes

Correction: What magnetic resonance imaging has told us about the pathogenesis of rheumatoid arthritis – the first 50 years

After publication of our recent article [1], we noticed an error in the legend of figure 2: “The marrow soft tissues have an increased water content due to the osteitis that is seen as a high signal on fat suppression MRI (grey squares), as shown in (b).” This sentence should refer to panel (b) in figure 1. The correct sentence is: The marrow soft tissues have an increased water content due to the osteitis that is seen as a high signal on fat suppressio

Approaches to the Design of Biotechnical Streambank Stabilization: Volume I—A Guide to the Literature

Streambank stabilization has traditionally been performed with riprap for which reliable design and installation procedures are available. Due to concerns about the environmental impact of riprap, there has been increasing interest in more natural biotechnical (or bioengineering) alternatives. A review of the litera­ture on biotechnical approaches to streambank stabilization has been per­formed, with a focus on those works that might be particularly useful in developing design guidelines or standards for the Indiana Department of Transportation. Works that synthesized the literature (up to about the year 2000) and so covered a broad range of topics, were examined, including monographs and manuals published by federal and state agencies. More recent publications were also found on narrower more specific topics, including the ecological effects of riprap and bio­technical approaches, advances in the geotechnical modeling of vegetation effects on bank stability, the effectiveness of biotechnical measures, and screening methods for selecting appropriate measures. Implications of the reviewed work for the development of design guidelines are discussed

Approaches to the Design of Biotechnical Streambank Stabilization: Volume II—A Field Assessment

As part of a larger project to develop guidelines for the design of biotechnical approaches to streambank stabilization to be included in INDOT standard designs and specifications, a field assessment was undertaken of 26 sites, of which 13 were INDOT sites. Multiple techniques were frequently installed in combination, which resulted in 47 samples of 12 different techniques at the 26 sites. Each site was visited at least once and the measures were visually inspected for evi­dence of damage either to the measure or to the streambank being protected. Some of the field assessments were supplemented by interviews with designers involved in the INDOT projects; the general merits of biotechnical techniques were discussed together with those of specific tech­niques that might be included in a standard design. The assessment resulted in grouping the techniques into three broad categories: i) typically reliable techniques that could be used where tolerance for bank instability is very low, and generally involving hard armor, ii) potentially reliable techniques where the tolerance for bank instability is low to moderate, and iii) techniques that are appropriate only for special circumstances or to be used only in combination with measures from the other two groups

Approaches to the Design of Biotechnical Streambank Stabilization: Volume III—Design Guidelines

A conceptual framework for the design of biotechnical streambank revetment is proposed. It is intended to be simple in practice, flexible in being widely applicable, familiar in retaining cer­tain aspects of current practice while being patterned after other aspects, and encouraging a more environmentally sensitive approach to reliable streambank protection for INDOT projects. It distinguishes between a toe zone, where traditional hard armoring techniques such as those already included in the INDOT standard designs are more appropriate, and an upper bank zone where vegetation-based techniques would typically be applied. Default techniques are identified to simplify the choice of measures for \u27routine\u27 problems, but more case-specific techniques may also be selected. Primary techniques that offer immediate protection on their own are also distin­guished from supplementary techniques that are used only in combination with other (primary) techniques. The boundary between the toe zone and the upper bank zone is proposed to be the maximum of the ordinary high water mark (or bankfull elevation), the elevation corresponding to the 2-year discharge, and the elevation corresponding to the point that is one third up the slope from the bank toe at the design discharge (for streambank protection). For the upper bank zone, for bank slopes up to 2H:1V, regrading and revegetation with herbaceous species together with the use of rolled erosion control products (RECPs) is proposed as the default. The other (non-default) main primary technique for the upper bank zone is the vegetated mechanically stabilized earth (VMSE, or vegetated reinforced soil slope VRSS, or soil lifts) option (where revegetation with herbaceous species is also considered standard). This requires more engineering and construct­ion effort but is appropriate for those projects where a more vertical (up to maximum bank slope of 1H:1V) solution is desired. The supplementary techniques to be included are live staking to be used with the regrading option, and brush-layering to be used with the VMSE option

Woodford Shale in Portions of Logan County, Oklahoma: Feasibility of Defining an Algorithm for Mapping and Exploration

The purpose of this study was to examine the well-log character of the Woodford Shale in portions of Logan Co., Oklahoma and define an algorithm for mapping the unit. Well-logs were examined. Structural geologic maps and isopach maps were created, based on the well-log data. Relationships among the well-logs were studied and cataloged. Variation within the Woodford Shale was determined, to give information concerning the structure and topography of the units bounding the formation. Defining categories for the types and characters of the Woodford stratagraphic boundaries allowed a methodology be derived to make mapping the unit more effective in the search for reservoirs and traps.Boone Pickens School of Geolog

A Laboratory Study of Apron-Riprap Design for Small-Culvert Outlets

The present study investigated primarily the appropriate stone-sizing of on-grade riprap aprons, and more specifically whether the current INDOT design policy may be overly conservative especially within the context of smaller culverts. In the study, laboratory experiments were performed with two pipe diameters, D = 4.25 in (0.35 ft) and 5.75 in (0.48 ft), and four stone sizes, median diameters estimated to be d50 = 0.61 in, 1.22 in, 1.73 in, and 2.24 in, for a range of discharges and tailwater depths. Video records were made of the laboratory apron to detect stone-mobilization events, and stable and unstable cases were distinguished. Logistic regression was then applied to develop equations delineating the boundary between stable and unstable regions for different riprap size classes in terms of d50/D. These regression equations were then modified to ensure that they formed an ordered system in that each equation was more conservative than the next, to include a safety factor, and to set a minimum size for each size class consistent with the applicability of each equation. Procedures for applying the proposed equations are described. Compared to the current INDOT design policy, the proposed approach typically predicts a smaller standard riprap class required for apron stability. In an application to a sample of actual culverts, the proposed approach, including the recommended safety factors, yielded a smaller required standard INDOT riprap class in 75% of cases, but, in a small number of cases with very low relative tailwater depths, did recommend a more conservative design. Of the other two main approaches to stone sizing for riprap aprons, the HEC-14 model was rather restricted in its range of application, but where applicable it was found to be somewhat more conservative in its stone-size recommendation, though in practice the recommended riprap class largely agreed with the proposed approach. The results of the other main approach, that due to Bohan (1970), were more erratic, with the maximum-tailwater equation being too lax and the minimum-tailwater equation being generally too stringent. Both the HEC-14 and the Bohan models tended to be less conservative than the proposed approach for larger values of d50/D. A secondary aim of the study was an examination of the velocity field downstream of the outlet, and the possible implications for scour downstream of the apron. Point velocity measurements were obtained for four cases, all with the same 4.25-in diameter pipe, three of which involved the largest (d50 = 2.2 in) stone, and one over a smooth bed. In the three cases with a stone apron, the apron extended a distance of ≈9D downstream of the outlet. In all four cases, substantial velocities (maximum velociites greater than 70% of than the average outlet velocity) were observed beyond 4D (which is the minimum specified by INDOT design guidelines) and even beyond 8D (which is the largest apron length specified in HEC-14). A comparison between rough-bed and smooth-bed results indicated a measurable effect on maximum velocity due to the rough apron, but the reduction in maximum velocity is still likely insufficient to prevent scour downstream of the apron in most practical cases even if the apron extends to 9D

Assessment of HY-8 and HEC-RAS Bridge Models for Large-Span Water-Encapsulating Structures

Current INDOT policy requires that culvert-like structures with spans greater than 20 ft be treated for purposes of hydraulic analysis as a bridge, and hence mandates the use of software such as HEC-RAS for predicting the headwater, rather than the culvert-specific software, HY-8. In this context, culvert-like structures are assumed to have a standard inlet geometry (e.g., such as those already modeled in HY-8) and a constant barrel geometry. The present study examines the technical basis of this policy, and whether the policy could be revised to allow the application of simpler culvert-hydraulics analysis and HY-8 to culvert-like structures with spans greater than 20 ft. Laboratory experiments were performed with model box culverts of span 1.5 ft and two streamwise lengths, 2.1 ft and 8 ft, and performance curves describing the variation of headwater with discharge were obtained. The effects of bed roughness, the presence or absence of a cover (if present, the rise was 0.5 ft), and a range of tailwater levels, were investigated. The laboratory observa­tions were compared with predictions by HY-8 and HEC-RAS models, and the model performance assessed. In general, HY-8 predictions were found to be as good as, and in some cases superior to, the HEC-RAS predictions, for both long and short culvert-like structures. This was attributed to the empirical information in HY-8 being more tailored to the specific standardized geometry of culvert-like structures, and the automatic inclusion of roughness effects, whereas HEC-RAS, at least when used with default coefficients and settings, relied on generic coefficients and neglected roughness effects. It was therefore recommended that a change in INDOT policy allowing large-span culvert-like structures to be analyzed using conventional culvert hydraulics would be technically justified for problems where the structure could be considered in isolation and accurate input data are available