Modeling Break Frequency Factor BFF

The need for a better understanding of the influence of maximum system pressure on breaks has recently been addressed by the IWA Water Loss Task Force's pressure management team. An extended data set of 112 systems from 10 countries as reported by Thornton and Lambert in IWA Water 218 is summarized in Table 10.10. The following can be noted:

• " Before" pressure (meters) ranges from 23 to 199, median is 57 and average 71.

• Percent pressure reduction ranges from 10 to 75%, median 33%, average 37%.

• Percent reduction in breaks ranges from 23 to 94%, median 50%, average 53%.

• The data shows no significant difference between average % break reductions on mains and service connections.

The data from Table 10.10 are also shown in Fig. 10.2 as a plot of % reduction in pressure versus % reduction in new break frequency, for mains and services together.

A simple interpretation, likely to give generally conservative predictions, is to assume that the % reduction in new breaks = BFF x % reduction in maximum pressure, where BFF is a break frequency factor, this can be checked against the data in Fig. 10.2.

The average value of BFF for mains and services together from Fig. 10.2 is 52.5%/ 38% = 1.4, so a line drawn through the data in Fig. 10.2 with a slope of 1.4 gives an average prediction.

An Upper line, with a BFF of 2.8 (twice the average) encompasses all but two of the data points which give larger reduction in new break frequencies

A 'Lower' line, with a BFF of 0.7 (half the average) encompasses all the data points which give smaller reductions in new break frequencies

When applying this simplified prediction approach, it is important to ensure that in cases where both the BFF and the % reduction in maximum pressure are both large, the prediction does not reduce the break frequency below the values used in the UARL formula.

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