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versus O relationship in half$-$foot increments for an underground cistern that is $2$ ft deep, $6$ ft long, and $3$ ft wide. A $6-$in$-$diameter drain on the side of the cistern acts as an orifice with a discharge coefficient of $0\mathrm{.}6.$ The invert of the drain is at the bottom of the cistern. Assume a routing interval of $10$ s$.$ A spreadsheet program may prove helpful.