What is the difference in peak runoff discharge (Q ) generated by a 2-acre urban roof area (rational runoff coefficient=0.85) versus a 4-acre lawn on heavy soil with the slope gradient of 2% (rational runoff coefficient=0.15), at the rainfall intensity of 0.3 in/hr (in cubic feet persecond, or cfs)? pk Lawn produces 0.33 cfs less runoff Lawn produces 0.51 cfs less runoff Lawn produces 0.18 cfs less runoff Lawn produces 0.18 cfs more runoff Lawn produces 0.33 cfs more runoff Lawn produces 0.51 cfs more runoff Roofs and the lawn produce the same amount of runoff