An engineer is to design a channel lined with planed wood to carry water at a flowrate of \(2 \mathrm{~m}^{3} / \mathrm{s}\) on a slope of \(10 \mathrm{~m} / 800 \mathrm{~m}\). The channel cross section can be either a \(90^{\circ}\) triangle or a rectangle with a cross section twice as wide as its depth. Which would require less wood and by what percent?