A detention pond has the shape of an inverted truncated pyramid, shown in Figure (a). It h...

A detention pond has the shape of an inverted truncated pyramid, shown in Figure (a). It has a rectangular bottom of dimension 120 × 80 ft, a maximum depth of 5 ft, and uniform side slopes of 3:1 (horizontal:vertical). Hence the dimensions at 5-ft depth are also rectangular, with length 150 ft and width 110 ft. The outlet from the basin behaves as an orifice, with a diameter of 1 ft and a discharge coefficient of 0.9. The opening of the orifice (a pipe draining from the center of the basin) is effectively at a depth of zero (i.e., at the bottom of the pond). (The pond floor would typically slope toward the outlet, but this slope will be ignored in this problem. In addition, the orifice will be assumed to follow its theoretical behavior even at very small depths.)

(a) What is the total volume of the pond, in ft3 and ac-ft?

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(b) Develop the depth-vs.-surface-area and depth-vs.-volume curves for the pond. Use 1-ft intervals. Tabulate and plot.

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(c) A triangular inflow hydrograph is shown in Figure (b). Route it through the detention pond. The storage indication method (Puls method) of Section 4.3 is recommended, with a time step of 10 min. Plot the outflow hydrograph on the same graph as the inflow hydrograph.