A two-stage storage routing model for green roof runoff detention

Green roofs have been adopted in urban drainage systems to control the total quantity and volumetric flow rate of runoff. Modern green roof designs are multi-layered, their main components being vegetation, substrate and, in almost all cases, a separate drainage layer. Most current hydrological models of green roofs combine the modelling of the separate layers into a single process; these models have limited predictive capability for roofs not sharing the same design. An adaptable, generic, two-stage model for a system consisting of a granular substrate over a hard plastic “egg box”-style drainage layer and fibrous protection mat is presented. The substrate and drainage layer/protection mat are modelled separately by previously verified sub-models. Controlled storm events are applied to a green roof system in a rainfall simulator. The time-series modelled runoff is compared to the monitored runoff for each storm event. The modelled runoff profiles are accurate (mean Rt 2 = 0.971), but further characterization of the substrate component is required for the model to be generically applicable to other roof configurations with different substrate

Residence Time Distributions for Turbulent, Critical and Laminar Pipe Flow

Longitudinal dispersion processes are often described by the Advection Dispersion Equation (ADE), which is analogous to Fick’s law of diffusion, where the impulse response function of the spatial concentration distribution is assumed to be Gaussian. This paper assesses the validity of the assumption of a Gaussian impulse response function, using Residence Time Distributions (RTDs) obtained from new laboratory data. Measured up- and down-stream temporal concentration profiles have been deconvolved to numerically infer RTDs for a range of turbulent, critical and laminar pipe flows. It is shown that the Gaussian impulse response function provides a good estimate of the system’s mixing characteristics for turbulent and critical flows, and an empirical equation to estimate the dispersion coefficient for Reynolds Number, Re, between 3,000 and 20,000 is presented. For laminar flow, here identified as Re < 3000, the RTDs do not conform to the Gaussian assumption due to insufficient time being available for the solute to become cross-sectionally well mixed. For this situation, which occurs commonly in water distribution networks, a theoretical RTD for laminar flow that assumes no radial mixing is shown to provide a good approximation of the system’s mixing characteristics at short times after injection

Computational fluid dynamics modelling of residence times in vegetated stormwater ponds

Experimental data characterising dispersion within Typha latifolia were previously collected in a laboratory setting. This mixing characterisation was combined with previously proposed computational fluid dynamics modelling approaches to predict residence time distributions for vegetated stormwater treatment pond layouts (including a wetland) derived from Highways England design guidance. The results showed that the presence of vegetation resulted in residence times closer to plug flow, indicating significant improvements in stormwater treatment capability. The new modelling approach reflects changes in residence time due to mixing within the vegetation, but it also suggests that it is more important to include vegetation within the model in the correct location than it is to accurately characterise it. Estimates of hydraulic efficiency suggest that fully vegetated stormwater ponds such as wetlands should function well as a treatment device, but more typical ponds with clear water need to be designed to be between 50% and 100% larger than their nominal residence times would suggest when designed against treatment criteria

Predicting manhole mixing using a compartmental model

Manholes in combined sewers may become surcharged during storm events, resulting in complex mixing conditions. Although manhole hydrodynamics are reasonably well understood, predicting mixing across a surcharged manhole remains a challenge. An analytical compartmental mixing model for manholes, based on jet theory, has been further developed and applied to generate cumulative residence time distributions (CRTDs), which describe mixing. The modeled CRTDs were compared with the experimentally derived CRTDs of over 850 manhole configurations to evaluate how well the new compartmental model represents physical processes. The model underpredicts short-circuiting in manholes with manhole diameter to pipe diameter ratios greater than 4.4 and consequently overestimates mixing. Otherwise, the modeled CRTDs show good agreement with the experimental CRTDs. The new compartmental model represents key manhole hydrodynamics that are not represented in current software modeling packages, which assume manholes are instantaneously well-mixed. The compartmental model provides good predictions of the experimental downstream concentration profiles, although with reduced peak concentrations in those manhole configurations where short-circuiting is not well-predicted. Despite this, the compartmental model still predicts concentrations downstream of a manhole in closer agreement with the recorded data than the complete instantaneously well-mixed assumption. As an analytical model requiring no inputs other than manhole geometry, the new compartmental model applies to a wide range of manhole configurations, is robust, and is useful for predicting manhole mixing in practical applications

The impact of cylinder diameter distribution on longitudinal and transverse dispersion within random cylinder arrays

Numerous studies focus on flow and mixing within cylinder arrays because of their similarity to vegetated flows. Randomly distributed cylinders are considered to be a closer representation of the natural distribution of vegetation stems compared with regularly distributed arrays. This study builds on previous work based on a single, fixed, cylinder diameter to consider non-uniform cylinder diameter distributions. The flow fields associated with arrays of randomly distributed cylinders are modeled in two dimensions using the ANSYS Fluent Computational Fluid Dynamics software with Reynolds Stress Model turbulence closure. A transient scalar transport model is used to characterize longitudinal and transverse mixing (Dx and Dy) within each geometry. The modeling approach is validated against independent laboratory data, and the dispersion coefficients are shown to be comparable with previous experimental studies. Eight different cylinder diameter configurations (six uniform and two non-uniform) are considered, each at 20 different solid volume fractions and with seven different transverse positions for the injection location. The new dispersion data cover a broad range of solid volume fractions, for which simultaneous estimates of Dx and Dy have not been available previously. There are no systematic differences in non-dimensional Dx and Dy between uniform and non-uniform cylinder diameter distributions. When non-dimensionalized by cylinder diameter, both dispersion coefficients are independent of solid volume fraction. When non-dimensionalized by cylinder spacing, both longitudinal and transverse dispersion can be described as linear functions of the ratio of cylinder diameter to cylinder spacing

Longitudinal dispersion in unsteady pipe flows

Temporal concentration profiles resulting from an injected pulse of fluorescent tracer were recorded at multiple locations along a pipe during controlled unsteady flow conditions. A linear temporal change in discharge over durations of 5, 10, or 60 s for both accelerating and decelerating flow conditions was studied. Tests were performed for flows that changed within the turbulent range, between Reynolds numbers of 6,500 and 47,000, and for laminar to turbulent flows, between Reynolds numbers of 2,700 and 47,000. Analysis of the data shows the limitations of employing steady-state routing of temporal concentration profiles in unsteady flows. Employing a ‘flow weighted time’ routing approach, using tracer mean velocity and dispersion coefficients, provides accurate predictions of mixing in unsteady flow. For decelerating flows, longitudinal dispersion coefficients were lower than for the equivalent mean steady discharge. Previously unreported disaggregation of the tracer cloud was observed during all experiments accelerating from laminar to turbulent conditions

Illuminating collaboration in emergency health care situations:Paramedic-physician collaboration and 3D telepresence technology

Introduction. This paper focuses on paramedics\u27 perspectives regarding paramedic-physician collaboration today, and their perspectives regarding the potential of 3D telepresence technology in the future. Method. Interviews were conducted with forty practicing paramedics. Analysis. The interview data were analysed using open and axial coding. An agreement of 0.82 using Cohen\u27s kappa inter-coder reliability measure was reached. After coding was completed themes and relationships among codes were synthesised using topic memos. Results. Paramedics expressed concern about the lack of respect and trust exhibited towards them by other medical professionals. They discussed how they paint the picture for physicians and the importance of the physician trusting the paramedic. They further reported 3D telepresence technology would make their work visible in ways not previously possible. They also reported the technology would require additional training, changes to existing financial models used in emergency health care, and increased access to physicians. Conclusions. Teaching collaboration skills and strategies to physicians and paramedics could benefit their collaboration today, and increase their readiness to effectively use collaboration technologies in the future

Illuminating Collaboration in Emergency Helath Care Situations: Paramedic-Physician Collaboration and 3D Telepresence Technology

Introduction. This paper focuses on paramedics' perspectives regarding paramedic-physician collaboration today, and their perspectives regarding the potential of 3D telepresence technology in the future. Method. Interviews were conducted with forty practicing paramedics. Analysis. The interview data were analysed using open and axial coding. An agreement of 0.82 using Cohen's kappa inter-coder reliability measure was reached. After coding was completed themes and relationships among codes were synthesised using topic memos. Results. Paramedics expressed concern about the lack of respect and trust exhibited towards them by other medical professionals. They discussed how they paint the picture for physicians and the importance of the physician trusting the paramedic. They further reported 3D telepresence technology would make their work visible in ways not previously possible. They also reported the technology would require additional training, changes to existing financial models used in emergency health care, and increased access to physicians. Conclusions. Teaching collaboration skills and strategies to physicians and paramedics could benefit their collaboration today, and increase their readiness to effectively use collaboration technologies in the future

A stem spacing‐based non‐dimensional model for predicting longitudinal dispersion in low‐density emergent vegetation

Predicting how pollutants disperse in vegetation is necessary to protect natural watercourses. This can be done using the one-dimensional advection dispersion equation, which requires estimates of longitudinal dispersion coefficients in vegetation. Dye tracing was used to obtain longitudinal dispersion coefficients in emergent artificial vegetation of different densities and stem diameters. Based on these results, a simple non-dimensional model, depending on velocity and stem spacing, was developed to predict the longitudinal dispersion coefficient in uniform emergent vegetation at low densities (solid volume fractions < 0.1). Predictions of the longitudinal dispersion coefficient from this simple model were compared with predictions from a more complex expression for a range of experimental data, including real vegetation. The simple model was found to predict correct order of magnitude dispersion coefficients and to perform as well as the more complex expression. The simple model requires fewer parameters and provides a robust engineering approximation