at the end of the month the ...

at the end of the month the lake water surface elevation is 103.2581m.

the steps are as follows

Given:

initial lake water surface elevation (Hi) =103.2m

inflow to the lake (Qi) = 6.0 m3/s = 6 m3/s * 3600 s/hr *24 hr/day * 30 day/month = 15,552,000 m3 , express in depth by dividing in to the area = 0.31104 m

outflow from the lake (Qo) = 6.5 m3/s = 6.5 m3/s * 3600 s/hr *24 hr/day * 30 day/month = 16,848,000 m3  = 0.33696 m

precipitation (P) = 145 mm = 0.145 m

evaporation from the lake (E) = 6.10 cm = 0.061 m

lake surface area = 5000 ha = 5 *10^7 m2

SOLUTION

Ho at the end of the month = Hi + (all inflows (gain) - all out floss (loss))

= 103.200 m + (0.31104+0.145 - (0.33696+ 0.061)) m

=103.200 m + 0.05808 m

Ho = 103.2581 m