A drainage basin bordering the sea has an area of 7500 km2 . The average precipitation for this drainage basin is 900 mm year-1 . The average surface water flow at the outlet of the drainage basin equals 22.5 × 108 m3 year-1 . The average groundwater flow to the sea is 100 mm year-1 . The averages are determined for 30 hydrological years. Determine the average actual evaporation in mm year-1 and m3 year-1.

Answer :

Answer:

[tex]7.8 \times 10^8 m3/y[/tex]

[tex]104 mm / yr[/tex]

Explanation:

Given data:

Basin Area = 7500 km^2

average precipitation [tex]= 900 mm year^{-1}[/tex]

average surface flow [tex]= 22.5\times 10^8 m^3 year^{-1}[/tex]

average ground flow[tex] = 100 mm year^{-1}[/tex]

total time period for averages = 30 hydrological year

Volume = height * area ,

here, height of precipitation

total precipitation over the surface [tex]= (900 * 10^{-3}) [/tex]

[tex]volume  = (900 * 10^{-3}\times (7500 * 10^6) )m3/yr = 37.8\times 10^8 m3/yr[/tex]

volume of flow of Groundwater to sea

[tex] = ( (100 * 10^{-3}) \times (7500\times 10^6) )m3/yr = 7.5\times 10^8 m3/yr[/tex]

Average surface flow [tex]= 22.5 \times 10^8 m3/yr[/tex]

The evaporation volume is given as

* Precipitation = Evaporation + surface  flow + groundwater flow.

therefore, we have

Evaporation = Precipitation - (surface water flow + groundwater flow)

putting all value in above equation to get evaporation value

Evaporation [tex]= 37.8 \times 10^8 m3/yr - ( 7.5 \times 10^8 + 22.5\times 10^8 ) m3/yr = 7.8 \times 10^8 m3/yr[/tex]

obtained height of water by dividing above calculated volume of evaporation by total area

[tex]= \frac{7.8 * 10^8 m^3}{75 * 10^8 m^2} = 0.104 m = (0.104 \times 1000) mm = 104 mm / yr[/tex]

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