Question

3. Consider the following situation and answer the subsequent questions to the best of your engineering ability and judgment. a. There are two Schultz Creek watersheds, East and West. The East drains into unincorporated communities east of Flagstaff, and the West drains into the City of Flagstaff itself. The key point about ‘unincorporated’ is that this means these residents did not live in a city or town, and for some infrastructure aspects like storm drainage, there were no requirements or regulations. Prior to 2010 both of these watersheds were heavily forested and due to almost a hundred years of fire suppression instead of fire management, both watersheds had accumulated thick, water-absorbing masses of pine needles and decomposed pine needles on the forest floor. This prevented the watersheds from ‘delivering’ runoff to its streams in normal years because all of the precipitation was stored in the pine needle layers, sometimes referred to as ‘duff’. Only in heavy snow and rain years, about once every 5-7 years, would the streams flow, instead of every one or two years. i. The East Schultz Creek Watershed is approximately 14 square miles in area. The West is about 6 square miles in area. Assume that the following hydrologic soil group percentages hold for both watersheds prior to 2010: 5% HSG D, 8% HSG C, 15% HSG B, and the rest is HSG A, due to the extensive duff in the watershed.

Answer 1