Question

A 4,000-km^2 watershed receives 102cm of precipitation in one

year.The avg. flow of the river draining the watershed is 34.2
m^3/s.Infiltration is est. to be 5.5 x 10^(-7) cm/s
andevapotranspiration is est. to be 40 cm/y. Determine the change
instorage in the watershed over one year. The ratio of runoff
toprecipitation (both in cm) is termed the runoff
coefficient.Compute the runoff coefficient for this
watershed.

Answer 1

1) The change in storage of the catchment is 707676800 cubic meters.

2) The runoff coefficient of the catchment is 0.83.

Step-by-step explanation:

The water budget equation of the catchment can be written as

`P+Q_(in)=ET+\Delta Storage+Q_(out)+I`

where

'P' is volume of precipitation in the catchment =
`Area* Precipitation`

`Q_(in)` Is the water inflow

ET is loss of water due to evapo-transpiration

`\Delta Storage` is the change in storage of the catchment

`Q_(out)` is the outflow from the catchment

I is losses due to infiltration

Applying the values in the above equation and using the values on yearly basis (Time scale is taken as 1 year) we get

`4000* 10^(6)* 1.02+0=0.40* 4000* 10^(6)+\Delta Storage+34.2* 3600* 24* 365* 5.5* 10^(-9)* 4000* 10^(6)* 3600* 24* 365`

`\therefore \Delta Storage=707676800m^3`

Part b)

The runoff coefficient C is determined as

`C=(P-I)/(P)`

where symbols have the usual meaning as explained earlier

`\therefore C=(102-5.5* 10^(-7)* 3600* 24* 365)/(102)=0.83`