A catchment has a runoff coefficient of 0.42, area = 85 ha with a general slope of 1 in 200 and maximum length of travel of overland flow of 1.8 km. Information on the storm of 25 years return period is given as follows: Duration (min) 15 Rainfall (mm) 40 Estimate the peak flow to be drained by a culvert for a 25 year storm Land use Roads Lawn Residential area Industrial area 30 60 Area (ha) If in the urban area of (a), the land use of the area and the corresponding runoff coefficients are as given below, estimate the new discharge. i = 2.78x155 2 80 000 170 000 45 500 000 100 000 -75 6.0 100 80 120 Runoff coefficient 0.70 0.10 0.30 0.80

2 %V9 li. 3 (9 This question requires one response per row The base flow for this direct runoff hydrograph is: 0 4 8h o Index = 0.135 cm/h Rainfall excess = 5.52 cm 30 25 20 15 Direct runoff 5.52 cm 10 A Base flow -6 0 12 18 24 30 36 42 48 54 60 66 Time in hours -6 8 5.52 48 Discharge (m/s) 3.26 cm 2.26cm

1. A 160-acre drainage basin has the following characteristics: Land Use Residential, flat, 60% impervious Residential, flat, 30% impervious Concrete or sheet asphalt pavement Turf Meadows Forested Area * for a range of values, the runoff coefficient can be calculated as an average value. Rainfall Intensity (in/hr) Find the peak runoff from the drainage area for a 20-minute duration storm with a return frequency of 25-years? 20 18 16 14 2 0 0 Frequency (years) 100 50 25 10 10 Area % 20 30 5 25 20 20 30 Duration (min) Coefficient (C)* 0.55 0.40 0.85 0.25 0.2 40 50 60

Use the TR-55 method to estimate the time of concentration for following watershed if the 2-year 24-hr rainfall is 2.5 in. Flow path A → B B → C C → D D → E D B Description Overland flow, dense grasses Shallow concentrated flow, unpaved surfaces Channel flow, rectangular channel, bottom width 2 ft, depth 1.5 ft, Manning's n = 0.04 Channel flow, trapezoidal channel, bottom width 4 ft, depth 3 ft, side slope 2:1, Manning's n = 0.035 Slope Length (ft) 0.02 350 0.05 500 0.03 1000 0.005 1500

You are designing a drainage system for a residential site in Atlanta using a 10-year return period. The site has an area of 1 ha, a flow length of 100 m, an average slop of 1%, a Manning's number of 0.25 and Type B soil. Drainage regulations require that the kinematic wave equation be used to calculate the time of concentration. You are allowed to use either the rational method or TR-55 to calculate the peak runoff rate. It is suggested you used a runoff coefficient of 0.4, which is typical for residential sites. What curve number would be required for both the rational method and the TR-55 method to provide the same peak runoff rate?