CIV E 445 - APPLIED HYDROLOGY
SPRING 2014
LAB No. 5

  1. Refer to the San Diego County Hydrology Manual. Answer the following questions:

    • How many major rivers and creeks are there are in San Diego County draining to the Pacific ocean? Please list them from north to south.

    • What is the maximum average annual rainfall in San Diego County? Where is it located?

    • What is the minimum average annual rainfall in San Diego County? Where is it located?

    • What is the rainfall intensity for a 6-hour rainfall of 4 in with a time of concentration of 30 minutes?

    • What is the rational method runoff coefficient for a soil type C and percent imperviousness 80%?

    • What is the overland flow time for a watercourse distance of 100 ft, 1% slope, and runoff coefficient C = 0.55? Use both chart and formula.

    • What is the time of concentration (hr) for L = 1 mile, and S = 0.01? Confirm with formula, nomograph, and online calculator (Kirpich formula).

    • What is the design velocity and depth in a gutter with Q = 9 cfs and street slope 2.1%?

  2. Use ONLINE OVERLAND to calculate the variation of time of concentration with bottom slope in a watershed with the following dimensions and properties:

    • Rainfall depth = 24 cm

    • Runoff curve number CN = 100

    • Total rainfall duration tr = 12 hr

    • Number of points in cumulative rainfall distribution Np = 2

    • Dimensionless cumulative time for rainfall distribution T* : 0.,1.

    • Dimensionless cumulative depth for rainfall distribution D* : 0.,1.

    • Total simulation time Tt = 48 hr.

    • Number of time intervals Nδt = 96

    • Number of time intervals for printing Npr = 1

    • Fraction used to estimate reference discharge Fr = 0.5

    • Overland flow area A = 18 ha

    • Fraction of area in left plane Flp = 0.5

    • Manning coefficient for left plane nlp = 0.01

    • Rating exponent for left plane βlp = 2

    • Manning coefficient for right plane nrp = 0.01

    • Rating exponent for right plane βrp = 2

    • Length of channel Lch = 400 m

    • Manning coefficient of channel nch = 0.015

    • Bottom width of channel Bch = 2 m

    • Design depth of channel ych = 0.6 m

    • Side slope of channel z = 3

    Calculate the theoretical peak outflow. Then, set all slopes (planes and channel) to the following values: 0.01, 0.005, 0.002, 0.001, and 0.0005, and run ONLINE OVERLAND for each slope. Determine the time of concentration, that is the time to peak or time to equilibrium of the calculated outflow hydrograph. What conclusion can you reach from the results?