Charting the urban skyscape

Software has the ability to prescribe water pressure reduction in the vicinity of tall buildings. Mouchel's operations director Richard Ingham explains how this is helping Thames Water with leakage reduction

As part of AMP4, Thames Water has been implementing its ongoing Network Improvement Programme. It focuses on both zonal reconfiguration and pressure management activities, with pressure reduction highlighted as one method for reducing leakage.

Since late 2006, as one of the programme's initiatives, the company has been testing a piece of web-based software, the Tall Building Database (TBD). It will assist its modellers and designers to better manage water pressures on sections of its network.

The TBD does not directly reduce leakage, but it can be used in the design stages of a pressure management scheme to reduce demand and control leakage. One year on, TBD has reduced the number of buildings that require an internal survey by about 30%, delivering significant internal time and cost savings for walking surveys.

It has also recommended new pressure management area (PMA) configurations, reducing water pressures in key locations and, in turn, reducing leakage levels. The TBD has not solved problems that could not be remedied before its implementation, but it has significantly improved the efficiency with which pressure reduction is controlled.

The TBD originally derived from a need to standardise the approach for assessing the effect of pressure reductions on tall buildings in Greater London and the Thames Valley.

The standardised format allowed for subjective information to be quantified in a more consistent manner, by using questionnaires, which primarily focused on the assessment of building heights. This data provided a more consistent format for reporting. To aid the data collection, a website was created which could be updated by any individual with a username and password. When the data was collated, the website provided a single, centralised set of results.

This early web-based application provided a number of immediate benefits to Thames Water during its pressure management activities. Adjusting water pressure in the vicinity of tall buildings that have not been identified in the early stages of a modelling project can cause significant delays to the delivery time of leakage-saving activities. At the same time, Thames Water realised that the tool had the potential to provide a much more comprehensive service for its conceptual designers.

To help to develop the database, Thames brought in water consultant Mouchel.

Mouchel then began sourcing a number of other parameters to complement the building height data, part of a five-month development process. This included ground height and topographic address data, in addition to the more traditional postal address data.

To provide the topographical data, a light detection and ranging survey was commissioned. The remote sensing technique uses optical technology to determine the distance between a source and a surface.

The initial survey of eight zones in central London, later expanded to include every zone inside the M25, created a data set that could be used to generate a detailed digital terrain model (DTM). The DTM provided a height value for every square metre that was accurate to within 100mm.

This information was then integrated with Thames's existing geographic information system (GIS) data. The initial eight-zone data alone produced more than 3Gb of information.

Ordnance Survey data was also used to provide map and address information. This is the system to represent topographic heights and reference points, as well as the boundary locations for all PMAs and supply zones. When the initial parameters had been incorporated, Mouchel programmed the software with the help of consultant GIS4Business, which provided technical support.

When completed, the final TBD comprised four separate modules - project management, analysis, survey, and reporting. These could be used in a systematic way to estimate the effect of pressure reduction on tall buildings.

The TBD trial in Thames Water's Crouch Hill zone - a 30km2 area incorporating 320,000 properties, covering Tottenham down to the City of London - has seen a massive improvement. Prior to the database's introduction, tall building surveys involved street-by-street walking. Tall buildings were then subsequently identified and scheduled for an internal survey to establish if the building already had a booster in place, and therefore whether the building was at risk from changes to network pressures.

The use of the TBD in Crouch Hill has allowed for roof heights, ground levels adjacent to buildings and current and proposed network pressures to be calculated instantaneously. The user can also make changes to area, flow and pressure parameters, as well as costing information, from which important engineering decisions can be made. The system automatically makes allowances for frictional losses in buildings' internal plumbing and the amount of useable pressure that might be required.

By pulling together all the data, enabling the designer to facilitate more accurate forecasting and analysis of project parameters, TBD has also reduced the risk of Thames Water's tall buildings being overlooked at the conceptual design stage of projects. It has also enabled its conceptual designers to make important decisions within very short time scales. Crouch Hill has a target of saving 5-6Ml of water a day through leakage reduction. Using the database, Crouch Hill is well on track to making this efficiency saving.

Mouchel will manage the TBD, controlling security, server access, data-sets, maintenance and software licensing. It is also investigating updating the system with further tools, such as automatically logging the history of communication for each building, including storing emails. An additional functionality will allow the user to schedule infrastructure events within each DMA and to automatically assess the number of buildings at risk.

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