The purpose of this assignment is to investigate the hydrologic impacts of building the Shopping Mall on a 30- acre parcel. Consider a storm that lasts two hours with a constant rainfall intensity of 1.0 in/hr. a. What is the minimum pre-development peak runoff expected in this site in cfs? Assume all of the flow drains from the site to a single point. Assume the site was moderately sloped and mainly composed of sandy soil prior to development. b. For the same storm as part 'a', determine the minimum peak runoff (cfs) expected after construction. Assume the entire parcel of land is developed with retail. C. How many times more runoff volume is there from the site as a result of development? d. What is the infiltration volume before and after development? e. The Wal-Mart Super Center has a detention pond to manage stormwater flow. A crude estimate of the volume required for the detention pond is the excess volume of runoff produced by a site. Given a design water depth of 3 feet and including 1 foot of freeboard (a safety factor; 4 ft total), how large of an area (in acres) will need to be devoted to this detention pond? f. Name at least two methods or materials that could be incorporated into the site design that would decrease the stormwater runoff, Land Use Downtown business Single-family residential 0.70 -0.95 Surface Type Asphalt and concrete Roots 0.70 -0.95 0.30-0.50 0.75 -0.95 Multi-family residential 0.40 -0.75 Lawns, sandy soil, flat (7%) Heavy industrial 0.60-0.90 0.15-0.20 Lawns, silty/clay soil, Fiat (7%) 0.25 -0.35 The purpose of this assignment is to investigate the hydrologic impacts of building the Shopping Mall on a 30- acre parcel. Consider a storm that lasts two hours with a constant rainfall intensity of 1.0 in/hr. a. What is the minimum pre-development peak runoff expected in this site in cfs? Assume all of the flow drains from the site to a single point. Assume the site was moderately sloped and mainly composed of sandy soil prior to development. b. For the same storm as part 'a', determine the minimum peak runoff (cfs) expected after construction. Assume the entire parcel of land is developed with retail. C. How many times more runoff volume is there from the site as a result of development? d. What is the infiltration volume before and after development? e. The Wal-Mart Super Center has a detention pond to manage stormwater flow. A crude estimate of the volume required for the detention pond is the excess volume of runoff produced by a site. Given a design water depth of 3 feet and including 1 foot of freeboard (a safety factor; 4 ft total), how large of an area (in acres) will need to be devoted to this detention pond? f. Name at least two methods or materials that could be incorporated into the site design that would decrease the stormwater runoff, Land Use Downtown business Single-family residential 0.70 -0.95 Surface Type Asphalt and concrete Roots 0.70 -0.95 0.30-0.50 0.75 -0.95 Multi-family residential 0.40 -0.75 Lawns, sandy soil, flat (7%) Heavy industrial 0.60-0.90 0.15-0.20 Lawns, silty/clay soil, Fiat (7%) 0.25 -0.35
