Alan Fewkes

Modelling the performance of rainwater collection systems: towards a generalised approach

Abstract The collection of rainwater from roofs, its storage and subsequent use make a significant saving in the use of potable water. This paper investigates how spatial and temporal fluctuations in rainfall can be incorporated into behavioural models, which simulate the performance of rainwater collectors. Temporal variations are considered at two different time scales, that is daily and monthly intervals. The first model uses a daily time interval to model system performance. A set of rainwater collector performance curves for five geographic locations is developed. From the location-specific curves, a set of average curves is determined which is shown to be sufficiently accurate for estimating rainwater collector performance. The second model uses a larger time interval of one month. The effect of daily fluctuations in rainfall is incorporated into this model using a storage operating parameter. Values of the parameter were determined by matching the output from the daily model with that of the monthly model. Generally the rainwater collector performance predicted by the monthly model using average values of the storage operating parameter is shown to correlate well with the corresponding values determined using a daily time interval model. The monthly model provides a simple and versatile method of modelling the performance of rainwater collectors.

Water saving potential of domestic water reuse systems using greywater and rainwater in combination

For a sustainable urban future, society must move towards the goal of efficient and appropriate water use. Reuse of domestic greywater and rainwater has a significant role to play in this task. In this study, rainfall time series have been used in conjunction with estimates of domestic water appliance usage generated by the Monte-Carlo simulation technique to predict long term system performance. Model results show that changes in the attributes of household occupancy, roof area, appliance type and storage volume affect the water saving efficiency of a single store reuse system. Considering greywater and rainwater in combination, the greatest rate of increase of efficiency with storage size occurs in the range 0-100 litres. Further analysis of small volume storage and reuse indicates that savings of up to 80% of the WC flush water can be made with less than 50 litres storage. However, the collection of rainwater in addition to greywater in a single store reuse system offers little improvement in water saving efficiency. Small volume domestic water reuse systems lend themselves to application in the urban housing environment and therefore offer potential in the move towards a more sustainable city.

Measurement and modelling of quality changes in stored untreated grey water

Abstract This paper describes an investigation into stored untreated grey water quality processes and the development of a computer simulation for those processes. A laboratory study was carried out to investigate the changes in water quality with increasing residence time, and the results were used to calibrate and verify the model. Model results gave a good fit for dissolved oxygen (DO) concentrations, but only a reasonable fit for chemical oxygen demand (COD). Still, the main trends of model and laboratory COD data were broadly represented. Measurement and model results tend to confirm the initial hypothesis of four major processes in operation: settlement of suspended solids, aerobic microbial growth, anaerobic release of soluble COD from settled organic matter and atmospheric reaeration. Storing grey water for 24 h may significantly improve water quality through rapid settlement of organic particles, however, storage beyond 48 h leads to depleted DO levels and potential aesthetic problems. A more detailed model of COD fractions within grey water (with the relevant measured data) in conjunction with a characterisation of particulate settling velocities should lead to improvements in model predictions.

Simulating the performance of rainwater collection and reuse systems using behavioural models

The collection of rainwater from roofs and its storage and subsequent use make a significant saving in the use of potable water. The capacity of the rainwater store is important because it affects both system and initial costs. The investigation concentrates upon the use of behavioural models to simulate the performance of rainwater collectors. The input data, in time series form, is used to simulate the mass flows through the model, and will be based upon time intervals of a minute, an hour, a day or a month. A preliminary mapping exercise is described that evaluates the accuracy of behavioural models for the sizing of rainwater collection systems using different time intervals and different reservoir operating rules applied to a range of reservoir capacities and collection areas. The preliminary analysis indicated that the yield after spillage (YAS) reservoir operating algorithm based on a hourly time interval could be used as a standard against which other models could be compared and calibrated. The detailed analysis enabled constraints to be proposed for the application of hourly, daily and monthly models expressed in terms of storage fraction, S/AR, where S = storage capacity (m3 ), A = roof area (m2) and R = annual rainfall (m). Hourly models can be used for sizing small stores with a storage fraction below or equal to 0.01. Daily models can be applied to systems with storage fractions within the range 0.01 to 0.125. Monthly models are only recommended for use with storage fractions in excess of 0.125.

Method of modelling the performance of rainwater collection systems in the United Kingdom

The collection of rainwater from roofs, its storage and subsequent use make a significant saving in the use of potable water. The capacity of the rainwater store is important because it affects both system and initial costs. This paper describes the development of a behavioural model that simulates the performance of rainwater collectors located within the United Kingdom. The input data in time series form are used to simulate mass flows through the model based on a daily time interval. Rainfall time series from 11 different UK locations are used to simulate the performance of rainwater collectors for a range of roof areas, storage capacities and demands. A set of rainwater collector performance curves for each of the geographic locations is developed. From the location-specific curves a set of average curves is determined that is shown to be sufficiently accurate for estimating rainwater collection performance within the United Kingdom. Finally, the average performance curves are shown to be adequately represented by an exponential association type equation, resulting in a computationally efficient method of determining rainwater collector performance.

The perceived barriers to the inclusion of rainwater harvesting systems by UK house building companies

This work investigates the barriers that exist to deter the implementation of rainwater harvesting into new UK housing. A postal questionnaire was sent to a selection of large, medium and small house-builders distributed across the UK. Questions were asked concerning potential barriers to the inclusion of rainwater harvesting in homes separated into five sections; (1) institutional and regulatory gaps, (2) economic and financial constraints, (3) absence of incentives, (4) lack of information and technical knowledge, and (5) house-builder attitudes. The study concludes that although the knowledge of rainwater systems has increased these barriers are deterring house-builders from installing rainwater harvesting systems in new homes. It is further acknowledged that the implementation of rainwater harvesting will continue to be limited whilst these barriers remain and unless resolved, rainwater harvestings potential to reduce the consumption of potable water in houses will continue to be limited.

A review of rainwater harvesting in the UK

Purpose – The purpose of this paper is to provide a review of the technology, design and application of rainwater harvesting (RWH) systems in a UK context and identify areas of research and development.Design/methodology/approach – A comprehensive range of literature from 1978‐2010 is reviewed and divided into the following sections: history, application in developed countries, benefits of RWH, system categories and components, storage capacity, rainwater quality and factors influencing the use of RWH systems.Findings – This paper provides a useful source of information relating to the potential benefits of RWH systems, different types of system and components used to supply non potable water. To ensure the potential of RWH systems in the UK is realized, an integrated approach to their application is required. This may improve the financial viability of these systems and sustainability credentials but requires further research.Research limitations/implications – It is not an exhaustive list of publication...

An interdisciplinary approach to the assessment of water recycling technology options

Whilst work on the development of engineering options for water recycling has continued apace over the last decade, less attention has been paid to the problem of selecting appropriate technologies for particular applications. This paper firstly reviews the motivations for a cross-disciplinary approach to technology selection in this context, highlighting the process of translating research findings into practical and socially acceptable opportunities. It goes on to report early experience from an interdisciplinary collaboration which seeks to assess the suitability of specific water recycling options for urban environments. Conclusions relate primarily to the effective application of interdisciplinary research programmes to water management issues.

Investigating the sustainability of water management in Alwahat, Libya

Libya is known to suffer from water shortages due to its location in desert and semi-desert terrains. The population is growing in Libya and because of the continuing reliance on groundwater supplies; a strain has been placed on this water resource. As a consequence, levels of underground water are decreasing, making it difficult and costly to extract. The problem has been made worse by the shortage of rainfall experienced in Libya in recent years. The threat to water resources has brought into focus the urgent need for planned action to manage water resources effectively as it is widely acknowledged that water is a major limiting factor in the socio-economic development of the country with a rapidly expanding population. The paper collates data from various sources to provide an overview of water use in the case study area of Alwahat which demonstrates the need to develop a sustainable water management strategy.