Grant Wright

The performance characteristics of multi-outlet siphonic roof drainage systems

Siphonic roof drainage systems have been in existence for approximately 30 years, and are becoming an increasingly common element of urban drainage infrastructure. In that time, the construction sectorin most developed countries have been gradually persuaded of the benefits that these systems offer when compared to conventional roof drainage technologies. The work reported herein details anongoing UK government-funded research programme to investigate the performance characteristics of multi-outlet siphonic roof drainage systems. The experimental aims, apparatus and procedures are described, and results are illustrated. In addition, ‘real’ data obtained from three installed siphonic roof drainage systems are discussed. Conclusions are drawn regarding the performance characteristics of multi-outlet systems, and plans for future work are outlined.

Public attitudes towards flooding and property-level flood protection measures

The number of residential properties at risk from flooding is predicted to rise in the future, and it is clear that large-scale flood defence schemes are not always feasible. There is thus an increasing onus on the public to protect their own properties. This paper reports the results of a stakeholder consultation investigating public attitudes towards flooding and property-level flood protection (PLFP) in general, and peoples’ “willingness to pay” for PFLP specifically. The findings show that flooded households have suffered significant financial and social impacts. Despite some continued uncertainty surrounding flood risk responsibility, the majority of the public surveyed were willing to pay for PLFP, with a mean contribution of approximately £800. Whilst this paper broadly confirms some of the findings of earlier studies, it also indicates that public education and promotion campaigns have been effective in raising awareness and uptake of PLFP and that people are willing to pay more to protect their properties. The findings also support the notion that an increased awareness of PFLP, and an increased willingness to pay for PLFP, is linked to the scale of flooding and impacts, rather than just the frequency, as well as financial subsidies. The results of the study are particularly relevant to institutional stakeholders, as they can help guide the development of strategies to increase the uptake of such measures. Whilst the project focuses on the situation in Scotland, the findings will have resonance in similar countries throughout Europe and beyond.

Recent and future advances in roof drainage design and performance

The past 10 years have witnessed significant changes in the way roof drainage systems are understood and designed. In particular, there has been a stepchange in the confidence with which siphonic roof drainage systems may be specified and expected to perform. These changes have occurred whilst urban drainage design in general has been revolutionized by wider acceptance of Sustainable Urban Drainage Systems and greater public concern regarding pluvial flooding within the context of climate change. This text considers, in detail, both how roof drainage systems are designed and how they should be expected to perform. Particular attention is drawn to weaknesses in accepted design methods. Consideration is also given to ‘innovative’ roof drainage related approaches such as green roofs and rainwater harvesting. Practical application: Over the past few years there have been many changes in how roof drainage systems are specified and designed. On large buildings, technologies such as ‘siphonic roof drainage’ are now commonplace and there is an ever increasing demand for ‘green roofs’ to be specified due to their potential to ‘green’ developments. Based on ongoing research, this paper details how these different types of roof drainage solutions can be efficiently designed and what levels of performance can be expected.

Drainage ventilation for underground structures I: Transient analysis of operation

Below-ground structures provide special challenges to the designer of drainage systems, particularly if odour ingress is to be prevented to generally accepted standards. It is insufficient to rely on entrained airflow to ensure that the network is generally at below atmospheric pressures; fan-assisted venting is often required. Transient propagation as a result of both system appliance discharge and the operation of a fan-assisted vent system needs to be analysed to avoid system failure. This paper presents the necessary solution to the governing St Venant equations to allow system simulation. The basis for a numerical simulation is presented and the boundary conditions particular to this class of installation are identified.

Experimental study on the hydrological performance of a permeable pavement

Abstract Permeable pavements play an essential role in urban drainage systems, making them the subject of great interest to both researchers and practitioners. However, previous studies have demonstrated a significant degree of uncertainty regarding both the hydrological performance and the maintenance requirements of this type of pavement. Within this context, the presented research involved the construction of a one metre square surface area of permeable pavement and a laboratory rainfall simulator to investigate the influence of rainfall intensity on the hydrologic response of permeable pavements. The design of the permeable pavement complied with the SuDS Manual guidance and British Standards (BS 7533-13:2009). The laboratory test programme was designed to investigate the influence of rainfall intensity on the hydrologic response of permeable pavements. The results demonstrate that the hydrologic performance varied according to rainfall intensity. The total volume of discharge from the permeable pavement ranged between 8% to 60% of the inflow. More than 40% of the total rainfall from all rain events was temporarily detained within the structure. Permeable pavement design optimisation has therefore been tested in the study. The SuDS Manual guidance has been found to meet current optimisation requirements.

Investigation into the Performance Characteristics of Multi-Outlet Siphonic Roof Drainage Systems

Siphonic roof drainage systems have been in existence for approximately 30 years, and are becoming an increasingly common element of urban drainage infrastructure. In that time, the construction sector in most developed countries have been gradually persuaded of the benefits that these systems offer when compared to conventional roof drainage technologies. However, current design practice is based on steady-state theory and, arguably, simplistic assumptions. In response to perceived deficiencies in current design practice, a siphonic roof drainage research programme was initiated at Heriot-Watt University in 1996. This has led to a better understanding of the performance characteristics of siphonic systems, with particular reference to the priming of such systems (the purging of air from the system). This has resulted in the development of a numerical model capable of accurately simulating the priming phase of single outlet siphonic roof drainage systems. However, the majority of installed systems incorporate more than one roof outlet, and the interaction between such outlets is not well understood. It was therefore recognised that further research was required to extend the applicability of the existing numerical model to multi-outlet applications. The work reported herein details an ongoing UK government funded research programme to investigate the performance characteristics of multi-outlet siphonic roof drainage systems. The experimental aims, apparatus and procedures are described, and results are illustrated. In addition, “real” data obtained from three installed siphonic roof drainage systems are discussed. Conclusions are drawn regarding the performance characteristics of multi-outlet siphonic roof drainage systems, and plans for future work are outlined.

Australian water closet developments and their role in sustainable sanitation

Australias unique climatic and demographic conditions have resulted in a long standing appreciation of the importance of water conservation issues. With respect to sanitation provisions, this has resulted in the development of 6/3 litre dual flush water closets (WC). In addition to the obvious environmental benefits associated with using lower flush volumes, such technology has also had significant financial implications, both for the nation and the domestic consumer. This paper outlines the development of low flush volume WCs in Australia, along with other technologies aimed at improving the sustainability of the water based sanitation systems used in Australia and throughout the industrialized world.

Drainage ventilation systems for underground structures II: Simulation of transient response

The propagation of low-amplitude air pressure transients within the drainage and vent systems of underground habitable structures may result in system failure due to trap seal loss and foul odour ingress into the occupied space. This paper develops the simulation of such transient response, and presents comparisons between predicted system air pressures and those monitored during the operation of the drainage and vent system in a large London Underground tube railway station. The use of the model to investigate system operating regimes ahead of installation as a direct design aid is demonstrated.

Taking stock of community-based flood risk management in Malawi: different stakeholders, different perspectives

ABSTRACT Current flood risk strategies in Malawi are characterized by community-based flood risk management (CB-FRM), even though studies explicitly documenting evidence of successful CB-FRM remain limited. This paper investigates the realities and challenges of CB-FRM as seen through a lens of different stakeholders. In order to capture the experiences of CB-FRM, a predominantly qualitative research framework was developed. In 2016, 11 focus group discussions with stakeholder groups (local communities, local government and non-governmental organisations) were held. Additionally, informal discussions, field visits, a short survey and an extensive desk study were undertaken. The findings were analysed according to the major themes that emerged related to the realities and challenges of specific stakeholder groups. Although response and relief still remain prominent components of CB-FRM in Malawi, a number of mitigation and preparedness activities is observed. However, a lack of in-country resources, relief-oriented aid approaches and an ‘aid dependency’ syndrome represent obstacles. Different stakeholder groups share similar challenges in terms of financing, participation, decentralised governance and project management. Lack of project sustainability and localised ownership also emerged as major challenges. The identified challenges shed light on the frontiers and directions in which improvements are needed, thus offering a valuable contribution to the existing knowledgebase.

Modelling the failure modes in geobag revetments.

In recent years, sand filled geotextile bags (geobags) have been used as a means of long-term riverbank revetment stabilization. However, despite their deployment in a significant number of locations, the failure modes of such structures are not well understood. Three interactions influence the geobag performance, i.e. geobag-geobag, geobag-water flow and geobag-water flow-river bank. The aim of the research reported here is to develop a detailed understanding of the failure mechanisms in a geobag revetment using a discrete element model (DEM) validated by laboratory data. The laboratory measured velocity data were used for preparing a mapped velocity field for a coupled DEM simulation of geobag revetment failure. The validated DEM model could identify well the critical bag location in varying water depths. Toe scour, one of the major instability factors in revetments, and its influence on the bottom-most layer of the bags were also reasonably represented in this DEM model. It is envisaged that the use of a DEM model will provide more details on geobag revetment performance in riverbanks.