Eg:
The rainfall on 6 successive days in a catchment area is 4, 3, 5, 1, 7, & 2cm. The Φ-index for the stormwater is 3cm/day. Calculate the total volume of runoff, if the area of the catchment is 87km².
Calculation:
The total volume of runoff =?
The runoff/day
= [rainfall per day - Φ index]
Note:
1. Φ-index is the constant infiltration of rainwater that yields the actual runoff volume of the total rainfall water.
2. Rainfall rates equal to or lesser than Φ-index does not provide any volume for the runoff. Hence they are not taken while calculating the runoff.
Therefore,
Total runoff depth
= [(1st-day rainfall - Φ-index) + (3rd-day rainfall - Φ-index) + (5th-day rainfall - Φ-index)]
= [(4cm. - 3cm.) + ( 5cm. - 3cm.) + ( 7cm. - 3cm.)]
= [1cm. + 2cm. + 4cm.]
= 7cm. = 0.07m.
The total volume of runoff
= [total depth of runoff х catchment area]
First, let us convert the catchment area in m²
i.e. 87 km². = 87 х 10⁶ m²
The total volume of runoff
= [0.07m. х 87 х 10⁶ m² ]
= 6.09 х 10⁶ m³
or
The total volume of runoff = 6.09 MCM.
MCM 👉 Million cubic meters.
Thank you for going through these calculation steps❤. Have a good day 😄.
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