The farmer created a rectangular reservoir (length – 40 m, width – 20 m, depth – 2 m). He filled it halfway with water.

The farmer created a rectangular reservoir (length – 40 m, width – 20 m, depth – 2 m). He filled it halfway with water. How long will it take for the reservoir to be completely filled with water, if the average annual precipitation in this place is 800 mm / year, and the evaporation rate is 420 mm / year?

1) Let’s determine how much water is added to the reservoir annually due to atmospheric precipitation:
800 mm / year – 420 mm / year = 380 mm / year
2) The water level will rise by 380 mm per year. Let’s determine how long it takes the water level to rise by 1 m:
1 m: 380 mm = 1000 mm: 380 mm = 2.63 years or 2 years 7 months 17 days
Answer: the reservoir will be filled with water completely in 2 years 7 months 17 days.