In problem 16.3 a spreadsheet approach was demonstrated for solving the problem of calculating the..

In problem 16.3 a spreadsheet approach was demonstrated for
solving the problem of calculating the time variation of concentration in a
lake with variable inflow and outflow conditions. However, it may be noticed
that in March, the concentration at the end of the month is calculated to be
greater than either the concentration at the beginning of the month or the
inflow concentration. What is the problem? Develop a modified approach that
resolves this problem.

problem 16.3

Consider a small lake with one inflow and one outflow, as
sketched in Fig. 16.10. The inflow and outflow rates are not
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In problem 16.3 a spreadsheet approach was demonstrated for
solving the problem of calculating the time variation of concentration in a
lake with variable inflow and outflow conditions. However, it may be noticed
that in March, the concentration at the end of the month is calculated to be
greater than either the concentration at the beginning of the month or the
inflow concentration. What is the problem? Develop a modified approach that
resolves this problem.

problem 16.3

Consider a small lake with one inflow and one outflow, as
sketched in Fig. 16.10. The inflow and outflow rates are not necessarily equal,
nor are they constant. The average inflow and outflow rates on a monthly basis,
along with the average monthly inflow concentration of a contaminant of
interest, are shown in the first three columns of the spreadsheet below. Values
for Q are in m3/s and C is in mg/L. If the contaminant decays with rate 0.05
day1 and the concentration in the lake is 35 mg/L on January 1, calculate the
concentration at the end of the year. The lake volume on January 1 is 108
m3. Assume fully mixed conditions and no other sources or sinks.

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