A drainage ditch is to be built to carry runoff from a subdivision. The maximum design capacity is to be $1 \mathrm{million} \mathrm{gph}(\mathrm{gal} / \mathrm{h})$ and it is to be concrete lined. If the ditch has a cross section of an equilateral triangle, open at the top, and if the slope is $2 \mathrm{ft} / \mathrm{mile}$, what should the width at the top be?