Old catchments developed for over 20 years usually lack formalised overland flow paths. When "Old Urban" is selected the storage delay factor "B" is modified depending on the Return Period event being analysed to reflect extra sub-catchment storage.

Return Period

Multiplication Factor

1

1.30

3

1.15

5

1.00

10

1.10

20

1.35

50

1.50

100

2.00

Note:

If Old Urban option is not selected in the Catchment Data window, then B remains unmodified.