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depth and duration of flooding. 'Flood depth' was defined as the predicted maximum depth of flooding above ground level, while 'duration of flooding' was defined as the period over which water was present above ground level. Both were estimated for the selected nodes using the depth hydrographs produced by the model. |
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Figure 14.4 shows the variation in flooding depth at selected nodes with assumed system-wide solids depths during the largest event. The results show that maximum depth of flooding is, on an absolute scale, insensitive to solids levels. The maximum variation in flood depth between a clean drain and one that is 80 per cent blocked in this large event is only 9 cm. This may be explained by the large area over which water is spread once flooding occurs. In other words, when flooding takes place, the hydraulic capacity of the channel plays a relatively minor role in determining the depth of flooding. |
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The distributed nature of the drainage system explains the unlikely result of decreased depth of flooding as solids increase at |
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Figure 14.4
Maximum flood depth as a function of solids blockage (event of 5 September 1994) |
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