How to Calculate Annual Runoff || Problem & Solution ||

How to Calculate Annual Runoff || Problem & Solution ||

23rd July 2020 0 By Malay Sautya

How to Calculate Annual Runoff?

Mathematical Problem:

For a catchment in M.P., India, the mean monthly rainfall and temperatures are given. Calculate the annual runoff by Khosla’s formula.

MonthJanFebMarAprMayJuneJulyAugSepOctNovDec
Temp (°C)121621273134312928291914
Rainfall4420212322916212

Solution:

In Khosla’s formula,

Rm = Pm – Lm

Where,

  • Rm = Monthly runoff
  • Pm = Monthly rainfall in cm
  • Lm = (0.48 × T) Or Pm which ever is less.
  • T = Monthly temperature in degree.

1. For january month

Lm = (0.48 × 12) = 5.76

So, 5.76 is geter than the corrosponding Pm = 4.

So, the value of Lm will be taken as 4.

Now,

Rm = (Pm – Lm) = (4 – 4) = 0

2. For july month

Lm = (0.48 × 31) = 14.88

So, 14.88 is less than the corrosponding value of Pm = 32

So, we will take the value of Lm = 14.9

Now,

Rm = (Pm – Lm) = (32 – 14.88) = 17.1

I think you can able to solve rest of the months by using above method.

MonthJanFebMarAprMayJunJulAugSepOctNovDec
Rainfall (Pm)4420212322916212
Temp (°C)121621273134312928291914
Lm442021214.913.913.4212
Rm00000017.115.12.6000

So, the total annual runoff = ( 17.1 + 15.1 + 2.6) = 34.8 in cm.

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