Question 52

A directly connected portion (to the outlet) of an Adelaide catchment (total Area = A ha) was subjected to an industrial development. Travel time before the development was t_c minutes (to travel from the furthest point, P to the catchment outlet, O). After the development, travel time for the developed area is approximately t_c1 minutes and that is for the undeveloped area still equals to t_c. The runoff coefficients at 10-year ARI, C₁₀ for the undeveloped (pervious) and developed (impervious) areas are C₁ and C₂ respectively. Based on the data provided below, select the set of parameters for the analyses from the data. The IFD data (mm/hr) and Frequency conversion factors are given in Tables 4 and 5 respectively. (a) Based on the data selected, indicate developed and undeveloped areas on a typical catchment. Also indicate furthest point, P and the catchment outlet, O.

(b) Using Rational method of peak flow estimation, compute the percentage increase of the T-year (ARI = T years) design flood peak due to the development. All the calculations need to be presented logically and clearly.

Total Area (At)	tc (min)	tc1 (min)	C1 at 10-year ARI (previous)	C2 at 10-year ARI (impervious)	ARI (T years)	Developed area (% of At) = 30Total Area (At)
4	30	15	0.25	0.8	70	40

Table 4 Frequency conversion factor Ft (for questions 52 ARI (T-years) FI 1 0.8 2 0.85 5 0.95 10 1 20 1.05 40 1.13 60 1.17 80 1.19 100 1.2 Table 5 IDF data (mm/hr) for Adelaide region (for questions 52 Duration (min) 5 10 15 20 25 1 42.9 32.18 26.5 22.83 20.22 2 57.95 43.34 35.62 30.65 27.11 24.43 22.32 20.61 19.19 ARI = T (Years) 5 10 20 81.43 97.96 121.04 60.46 72.42 89.15 49.45 59.06 72.52 42.38 50.51 61.89 37.37 44.45 54.39 33.59 39.9 48.75 30.62 36.33 44.33 28.22 33.33 40.76 26.23 31.04 37.81 50 156.02 114.39 92.77 78.89 69.27 100 186.54 136.34 110.32 93.78 82.13 73.42 66.6 61.11 56.57 30 35 40 45 18.24 16.69 15.42 14.37 61.99 56.29 51.69 47.89 Table 4 Frequency conversion factor Ft (for questions 52 ARI (T-years) FI 1 0.8 2 0.85 5 0.95 10 1 20 1.05 40 1.13 60 1.17 80 1.19 100 1.2 Table 5 IDF data (mm/hr) for Adelaide region (for questions 52 Duration (min) 5 10 15 20 25 1 42.9 32.18 26.5 22.83 20.22 2 57.95 43.34 35.62 30.65 27.11 24.43 22.32 20.61 19.19 ARI = T (Years) 5 10 20 81.43 97.96 121.04 60.46 72.42 89.15 49.45 59.06 72.52 42.38 50.51 61.89 37.37 44.45 54.39 33.59 39.9 48.75 30.62 36.33 44.33 28.22 33.33 40.76 26.23 31.04 37.81 50 156.02 114.39 92.77 78.89 69.27 100 186.54 136.34 110.32 93.78 82.13 73.42 66.6 61.11 56.57 30 35 40 45 18.24 16.69 15.42 14.37 61.99 56.29 51.69 47.89