David A. Kelly

Raingardens offer a sustainable and nature-based approach to stormwater management and runoff control that provide multiple additional benefits to biodiversity, ecosystem services, and amenity, to name only a few. Raingardens vary in design and can be incorporated into a wide variety of urban landscapes, offering flexibility appropriate for the setting. The aim of this paper is to examine the hydrological performance and functionality of a raingarden installed in Edinburgh, Scotland over a prolonged period. Key characteristics of the raingarden are assessed and compared against the design. The raingarden was designed with two engineered soils: Engineered Soil 1 (retaining 30% existing soil–as recommended by the United Kingdom SuDs Manual) and Engineered Soil 2 (retaining 45% existing soil). We found that despite matching the recommended soil composition, the particle size distribution of Engineered Soil 1 showed variation from that recommended by the Manual. The key soil characteristics of bulk density, porosity, and saturated hydraulic conductivity correlated with the literature for both engineered soils and the existing soil. Whilst Engineered Soil 1 performed best in terms of its ability to intercept and drain runoff (having the highest saturated hydraulic conductivity, with fewer surface ponding events, and lowest retained soil moisture) it had lower soil storage capacity and plant available water than Engineered Soil 2. We also found distinct seasonal differences in infiltration performance in both engineered soils, with summer infiltration of Engineered Soil 1 being 2.5 times that of winter infiltration, and for Engineered Soil 2, summer infiltration was more than 1.4 times that of winter infiltration. Surface ponding in the raingarden was also found to be influenced by the season, with half of all ponding events occurring in winter when water uptake is reduced due to plants being dormant, and evapotranspiration is negligible. All ponding events de-watered within the recommended 48 h. Overall, the raingarden has been shown to retain 100% of runoff. The findings of this study provide helpful insight into key raingarden characteristics and functionality compared to design intent and should prove useful in informing future raingarden planning and implementation.

Reducing carbon emissions in buildings requires a holistic approach that extends beyond structural materials and looks at the services within, such as Building Drainage Systems (BDS). However, limited scientific research has addressed the environmental impacts of BDS, and, to date, no studies have systematically analysed embodied carbon emissions from a design code perspective. This study evaluates the embodied carbon emissions of BDS based on calculations from four major international design codes, BS EN 12056 (Europe), IPC and UPC (USA), and AS/NZS 3500 (Australia/New Zealand), using polyvinyl chloride (PVC) pipework. System configurations recommended in the design codes, such as primary ventilation and secondary ventilation systems, were evaluated as well as a fully active system incorporating Air Admittance Valves (AAVs) and Positive Pressure Relief Devices (PPRDs) across a range of building sizes from 10 to 100 storeys. The findings reveal substantial differences in recommended pipe sizes among the codes, directly impacting total pipework material use and, in turn, the embodied carbon emissions. A life cycle assessment (LCA) of PVC pipework demonstrates that the design recommendations in the European code generally lead to lower embodied carbon emissions, while the IPC and UPCs result in significantly higher emissions, with the AS/NZS code falling in between. In contrast, the use of a fully active drainage system was shown to reduce embodied carbon emissions by up to 73% depending on the building size and the design code applied. As the sustainability of buildings and systems becomes more and more vital, the findings of this paper provide the foundations for integrating the sustainability metrics of BDS into design codes. This will provide practical guidance for engineers and regulators on how carbon savings in BDS design and construction can be achieved.

The building drainage system (BDS) is a critical building component and must be designed to protect public health by maintaining safe and hygienic conditions within the indoor environment. The recent COVID-19 pandemic and the emergence of other wastewater-related issues, such as the spread of anti-microbial resistance (AMR), place the BDS at the centre of the public health agenda. To understand the complex characteristics of the BDS and its performance, the numerical simulation model AIRNET was used to model whole system responses to discharging events. In this study, the model’s effectiveness and accuracy were evaluated through its application in a case study system representative of a real-world tall building. Data reflecting actual conditions were collected using the drainage test rig at the National Lift Tower (NLT) in Northampton. The data show a strong correlation between the measured and modelled air pressures in the system over time and along the drainage stack height. More importantly, a sample dataset representing various ventilation configurations, flow rates, and water usage combinations shows a strong linear relationship between the simulated and measured pressure values. These results confirm the accuracy and reliability of the AIRNET model in modelling the BDS, even when applied to high-rise buildings. This is crucial for addressing drainage challenges in high-rise building design.

Blockages in sewers and drains often result in overflows and flooding that cause significant environmental pollution and public health risks, particularly in hospitals, where the consequences can be catastrophic. Due to their low “visibility”, sewers and drains are inherently difficult to monitor and maintain, resulting in a reactive management approach whereby maintenance or repair is carried out only after a system failure has occurred. This paper investigates the feasibility of applying the reflected wave technique, a unique sonar-like monitoring approach capable of identifying changes in the geometry of closed-pipe conduits, as a means of proactive system monitoring. The technique uses a 10 Hz sinusoidal air pressure wave which is transmitted into the drainpipe. When the pressure wave encounters a system boundary, a reflection is generated which alters the measured test pressure response. Analysis of the reflections generated by a changed system boundary, such as the formation of a blockage, can provide information related to the location of that boundary within the system. An experimental setup was developed to simulate a horizontal drain using standard pipework of 100 mm diameter and 70 m length. The technique was able to detect applied blockages with cross-sectional coverage of 30% and 75%, and lengths ranging from 30 mm to 3000 mm. Accuracy was improved when the pressure sensor was positioned closer to the blockage. When the sensor was 3.4 m from the blockage, location estimates were very accurate (−2% to 3% error). At a 14 m distance from the blockage, the error increased to between 4% and 33%. The accuracy of blockage detection and location improved with increasing blockage cross-sectional area and length. Overall, the reflected wave technique could provide a potentially continuous monitoring solution for blockage detection in sewers and drains.

Blockages in sewers and drains often result in overflows and flooding that cause significant environmental pollution and public health risks particularly in hospitals where the consequences can be catastrophic. Due to their low “visibility”, sewers and drains are inherently difficult to monitor and maintain, resulting in a reactive management approach whereby maintenance or repair is carried out only after a system failure has occurred. This study investigates the application of the reflected wave technique, a unique sonar-like monitoring system, capable of identifying changes to the geometry of closed-pipe-conduits, as a means of active system monitoring to enable maintenance to be conducted in a pro-active basis. An experimental setup was developed to simulate a horizontal drain using standard pipework of 100 mm diameter and 70 m length. Blockages representing 30% and 75% coverage of the drain’s cross-sectional area, with lengths from 30 mm to 3000 mm, were added to the drain. A sinusoidal air pressure wave of 10 Hz was applied and the resultant system pressure response recorded. All but the two smallest blockages (30% with 30 mm length and 30% with 100 mm length) were detected and located with good accuracy. The reflected wave technique could provide a novel and non-invasive method for blockage detection and overall system monitoring for sewers and drains.

Two-phase annular flow in vertical pipes is one of the most common and important flow regimes in fluid mechanics, particularly in the field of building drainage systems where discharges to the vertical pipe are random and the flow is unsteady. With the development of experimental techniques and analytical methods, the understanding of the fundamental mechanism of the annular two-phase flow has been significantly advanced, such as liquid film development, evolution of the disturbance wave, and droplet entrainment mechanism. Despite the hundreds of papers published so far, the mechanism of annular flow remains incompletely understood. Therefore, this paper summarizes the research on two-phase annular flow in vertical pipes mainly in the last two decades. The review is mainly divided into two parts, i.e., the investigation methodologies and the advancement of knowledge. Different experimental techniques and numerical simulations are compared to highlight their advantages and challenges. Advanced underpinning physics of the mechanism is summarized in several groups including the wavy liquid film, droplet behaviour, entrainment and void fraction. Challenges and recommendations are summarized based on the literature cited in this review.

A model is presented which allows steady-state pressure profiles in high-rise wastewater drainage networks to be related to intake air flowrates and discharge water flowrates. This model is developed using data taken from academic literature, and is based on experimental observations which suggest that a vertical annular downflow develops over distance such that the pressure gradient in the wet stack may be expressed as the sum of junction components and developed flow components. The model is used to analyse a simplified ‘medium rise’ primary vented system of height 40 m, hosting two inflow junctions, crossvents and Air Admittance Valves (AAVs). The model illustrates how the air supply configuration affects the airflow rates within the stack and the vents, and how the configuration affects the steady-state hydraulic pressure profile. The model offers the possibility of an alternative approach to the design of high-rise wastewater drainage networks, compared to existing design codes. These codes generally do not explain the role that the air admitted into the network has upon its performance.

National design guides provide essential guidance for the design of building drainage systems, which primarily ensure the basic objectives of preventing odor ingress and cross-transmission of disease through water-trap seal retention. Current building drainage system design guides only extend to buildings of 30 floors, while modern tall buildings frequently extend to over 100 floors, exceeding the predictive capability of current design guides in terms of operating system conditions. However, the same design guides are being used for tall buildings as would be used for low-rise buildings. A complicating factor is the historic roots of current design guides and standards (including the interpretation of the governing fluid mechanics principles and margins of safety), causing many design differences to exist for the same conditions internationally, such as minimum trap seal retention requirements, stack-to-vent cross-vent spacing, and even stack diameter. The design guides also differ in the size and scale of the systems they cover, and most make no allowance for the specific building drainage system requirements of tall buildings. This paper assesses the limitations of applying current building drainage system design guides when applied to the case of tall buildings. Primarily, the assessments used in this research are based on codes from Europe, the USA and Australia/New Zealand as representative of the most common approaches and from which many other codes and standards are derived. The numerical simulation model, AIRNET, was used as the analysis tool. Our findings confirm that current design guides, which have been out of date for a number of decades, are now in urgent need of updating as code-compliant systems have been shown to be susceptible to water-trap seal depletion, a risk to cross-transmission of disease, which is a major public health concern, particularly in view of the current COVID-19 pandemic.

Aerosols are readily transported on airstreams through building sanitary plumbing and sewer systems, and those containing microbial pathogens (known as bioaerosols) are recognized as contributors to infection spread within buildings. When a defect occurs in the sanitary plumbing system that affects the system integrity, a cross‐transmission route is created that can enable the emission of bioaerosols from the system into the building. These emission occurrences are characterized as short‐burst events (typically 99.5%) were 11 μm anywhere in the system. Particle count was influenced by toilet flush volume, but it was not possible to determine if there was any direct influence from airflow rate since both particle and biological data showed no correlation with upward airflow rates and velocities. Typical emissions resulting from a 6 L toilet flush were in the range of 280–400 particles per second at a concentration of typically 9–12 number per cm³ and a total particle count in the region of 3000 to 4000 particles, whereas the peak emissions from a 1.2 L toilet flush were 60–80 particles per second at a concentration of 2.4–3 number per cm³ and a total particle count in the region of 886 to 1045 particles. The reduction in particles is in direct proportion to the reduction in toilet flush volume. The slit‐to‐agar sampler was able to provide viable time course CFU data and confirmed the origin of the particles to be the tracer microorganism flushed into the system. The time course data also have characteristics consistent with the unsteady nature of a toilet flush.