4. The Russian River Has An Average Annual Peak Flow Of 48,000 Cfs. The Standard Deviation In The Annual Peak Flow Is 22,700 Sfs. (A) Assuming Annual Peak Flows Fit An Exponential Distribution, What Is The 100-Year Flood Flow? (B) Assuming Annual Peak Flows Fit A Normal Distribution, What Is The 100-Year Flood Flow? Table 15.2.3 Runoff Coefficients For Use

 

4. The Russian River has an average annual peak flow of 48,000 cfs. The standard deviation in the annual peak flow is 22,700 cfs. (a) Assuming annual peak flows fit an exponential distribution, what is the 100-year flood flow? (b) Assuming annual peak flows fit a normal distribution, what is the 100-year flood flow? Table 15.2.3 Runoff Coefficients for Use in the Rational Method Return period (years) Character of surface Developed Asphaltic Concrete/roof Grass areas (lawns, parks, etc.) Poor condition (grass cover less than 50% of the area) Flat, 0-2% Average, 2-7% Steep, over 7% Fair condition (grass cover 50% to 75% of the area) Flat, 0-2% Average, 2-7% Steep, over 7% Good condition (grass cover larger than 75% of the area) Flat, 0-2% Average, 2-7% Steep, over 7% Undeveloped Cultivated land Flat, 0-2% Average, 2-7% Steep, over 7% Pasture/range Flat, 0-2% Average, 2-7% Steep, over 7% Forest/woodlands Flat, 0-2% Average, 2-7% Steep, over 7% 25 10 25 50 100 500 0.73 0.77 0.81 0.86 0.90 0.95 1.00 0.75 0.80 0.83 0.88 0.92 0.97 1.00 0.32 0.34 0.37 0.40 0.44 0.47 0.58 0.37 0.40 0.43 0.46 0.49 0.53 0.61 0.40 0.43 0.45 0.49 0.52 0.55 0.62 0.25 0.28 0.33 0.36 0.38 0.42 0.30 0.34 0.37 0.41 0.53 0.45 0.49 0.58 0.37 0.40 0.42 0.46 0.49 0.53 0.60 0.21 0.23 0.25 0.29 0.32 0.36 0.49 0.29 0.32 0.35 0.39 0.42 0.46 0.56 0.34 0.37 0.40 0.44 0.47 0.51 0.58 0.31 0.34 0.36 0.40 0.43 0.47 0.57 0.35 0.38 0.41 0.44 0.48 0.51 0.60 0.39 0.42 0.44 0.48 0.51 0.54 0.61 0.25 0.28 0.30 0.34 0.37 0.41 0.53 0.33 0.36 0.38 0.42 0.45 0.49 0.58 0.37 0.40 0.42 0.46 0.49 0.53 0.60 0.20 0.25 0.28 0.31 0.35 0.39 0.48 0.31 0.34 0.36 0.40 0.43 0.47 0.56 0.35 0.39 0.41 0.45 0.48 0.52 0.58 Note: The values in the table are the standards used by the City of Austin, Texas. Source: Chow, Maidment, and Mays (1988).