Question 1128300: Situated in the northeastern portion of Oriental Mindoro, Naujan Lake is a freshwater
lake that has a surface area of 82 km2
. During October 2018, the lake evaporation was
measured to be 90 mm. Tigbao, Malbog, Maambog, and Cusay Creeks flow into the lake.
During the same month, the total inflow to the lake from these creeks was 35.90 m3
/s. At
the same time, the lake has only one outlet, Butas River, which has a total outflow of 40.2
m
3
/s from the lake. Also, for the same month, a water level increase of 100 mm for the
lake was observed. Using the water balance equation, what was the precipitation (in mm)
during that month?
Please help me with this my teacher gave this hw without discussing to us about it i tried to search for the formula but i dont know which is the correct one if possible can anyone assist me with this quesion?
Answer by KMST(5328)   (Show Source):
You can put this solution on YOUR website! I do not know of a formula,
and different teachers may use different formulas.
I believe formulas are for computers,
who cannot think for themselves.
Humans should be able to reason their way to their own formulas.
We know that
water entered the lake
X) from rain, and
A) from the creeks flowing into the lake, and
water exited the lake
B) through evaporation, and
C) through the Butas River.
That caused
D) an increase in the amount of water in the lake.
We can figure that
(water entering - water leaving = water increase in the lake).
It would make sense to express all those amounts of water in cubic meters.
That would take some calculations, because
the water entering and exiting through creeks and river is measured in cubic meters per second,
while the precipitation and evaporation are given in mm, apparently as total for the whole month.
The surface of the lake in square meters is
 
The level of the lake rose by
The water increase in the lake, in cubic meters can be estimated as
  
The evaporation from the lake, in cubic meters can be estimated as
 
The amounts of water coming in from the creeks and leaving through the Butas River are given in cubic meters per second,
and we have to calculate for a 31-day month with 24-hour days, and
 
The total inflow in cubic meters can be calculated as
 
The total outflow in cubic meters can be calculated as
 
Expressed all in cubic meters, looks like
That volume of water, expressed as precipitation falling over the
 of lake surface is
 
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