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

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.

Calculate Surface Area of Right Pri...
Calculate Surface Area of Right Prism Given the Volume
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.

Read More:

Types of Rainfall

Types of Irrigation

Methods of Improving Duty of Water