Extracted text: Watershed shown in the Figure 2-1 has three sub-catchment areas. Some properties of these sub- catchment areas are given in Table 2-1. (a) Using the given IDF curves and the Rational method, calculate the 50-years design peak flow (in cfs) at the catchment outlet. (b) A levee is to be designed to protect the area near to the catchment outlet using the estimated peak- flow. If the design life of the levee is 15 years, calculate the probability (%) of failure of the levee during its design life period. Area 1 A1 A2 Area 2 C1 C2 Table 2-1: Sub-catchment properties ti t2 Catchment property Area 1 Area 2 Area 3 Catchment area ( km²) 10 5 20 Area 3 Аз Runoff coefficient 0.25 0.75 0.5 C3 Time of concentration (minutes) 30 20 30 t3 Catchment outlet Figure 2-1: Watershed IDF curves for storms in vicinity of example site 9 9 8 7 6. 4 2+ 2 1t 05 10 15 20 30 40 50 60 70 80 90 100 110 120 130 Time (min) Intensity of rainfall (in./hr)