A 1000 acres watershed in the Bethlehem Township has the following characteristics: 900 acres of the watershed is an open space in good condition with Type C soil and 100 acres of the watershed is residential district and has average lots area as acre and average % impervious area as 25% with Type C soil. (a) Calculate the direct runoff Q for a 2-year, 24 hours storm assuming AMC II. (b) What is the time of concentration of this storm event give the following characteristics: Sheet flow: bare smooth soil, L_f = 50 ft, S_f = 0.01ft/ft; Shallow Concentrated Flow: Paved Gutter, L_sc= 400 ft, S_sc = 0.01ft/ft; Channel flow: grassed waterway with more stones, L₀ = 5000 ft, S₀ = 0.005ft/ft, A = 100 in²; P = 3 in. Use tables in Lecture 13 (p 17, p 21 and p 24) for necessary n values.

Values for Manning's n for overland flow are based TABLE 10.1: Manning's n for Overland Flow Surface type Manning's n Range Smooth concrete 0.011 0.010.014 Bare sand 0.01 0.01-0.016 Asphalt 0.012 0.010-0.018 Bare clay 0.012 0.010-0.016 Smooth earth 0.018 0.015-0.021 Graveled surface 0.02 0.012-0.030 Bare clay-loam (eroded) 0.02 0.012-0.033 Fallow (no residue) 0.05 0.0060.16 Cultivated soils (residue cover = 20%) 0.06 Bare smooth soil 0.10 Range (clipped) 0.10 0.020.24 Range (natural) 0.13 0.01-0.32 Sparse vegetation 0.15 Grass (short prairie) 0.15 0.100.25 Values for Manning's n for natural channel flow are based on surface type. NATURAL STREAM Minimum Normal Maximum 0.025 0.030 0.033 Type of Channel and Description 1. Minor Stream (top width at flood stage