A storm with a recorded precipitation of 11.0 cm, as shown in the table, produced a direct run-off of 6.0 cm. The $\emptyset$-index of this storm is ____________ cm/hr (rounded off to 2 decimal places).Time from start (hours) 1 2 3 4 5 6 7 8 Recorded cumulative precipitation (cm) 0.5 1.5 3.1 5.5 7.3 8.9 10.2 11.0
The $\emptyset$-index, also known as the infiltration index, is used to estimate the rate of infiltration during the period of a storm. It is calculated by dividing the volume of water infiltrated by the time over which the infiltration occurred.
Given:
- Total precipitation, $P=11.0\,cm$
- Direct runoff, $R=6.0\,cm$
The amount of infiltration, $F$, is given by:
$F=P-R=11.0-6.0=5.0\,cm$
We need to calculate the $\emptyset$-index over the entire duration of the storm, which is 8 hours. Therefore:
$\emptyset\text{-index}=\frac{F}{8\,hours}=\frac{5.0}{8}=0.625\,cm/hr$
Rounding off to 2 decimal places, the $\emptyset$-index is:
$0.63\,cm/hr$
This value does not fall within the provided range of 0.64 to 0.65. Verify calculations or conditions if there’s an expected range discrepancy.
Important Questions from Infiltration
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For a large catchment, contours joining points of equal monthly rainfall values were plotted. The plot is known as:
Which type of drainage system will collect the rainwater?
