CIV E 445 - APPLIED HYDROLOGY
SPRING 2014
LAB No. 6 SOLUTION

  1. The calculations are shown in the following table.

    [1] [2] [3] [4] [5] [6] [7]
    Time (h) Flow
    (m3/s)    		 Baseflow
    (m3/s)    		 Direct runoff hydrograph
    (m3/s)    		 Simpson's coefficients Direct runoff volume computation
    (m3/s)    		 Unit hydrograph ordinates
    (m3/s)
    0 1 1 0 1 0 0.00
    1 2 1 1 4 4 1.67
    2 4 1 3 2 6 5.00
    3 8 1 7 4 28 11.67
    4 12 1 11 2 22 18.33
    5 8 1 7 4 28 11.67
    6 7 1 6 2 12 10.00
    7 6 1 5 4 20 8.33
    8 5 1 4 2 8 6.66
    9 4 1 3 4 12 5.00
    10 3 1 2 2 4 3.33
    11 2 1 1 4 4 1.67
    12 1 1 0 1 0 0.00
    Sum (Σ) - - 50 - 148 83.33

    Direct runoff hydrograph:  Col. 4 = Col. 2 - Col. 3

    Direct runoff volume computation:  Col. 6 = Col. 4 × Col. 5

    Direct runoff volume, by Simpson's rule:   [(1 h × 3,600 s/h) / 3 ] × 148 = 177,600 m3

    Direct runoff depth:   [177,600 m3 / (29.6 km2 × 1,000,000 m2/km2] = 0.006 m = 0.6 cm

    Unit hydrograph ordinates:   Col. 4 / 0.6 cm

    The sum of Col. 7 is 83.33.

    Verification:   Σ Col. 4 / 0.6 = 50 / 0.6 = 83.33

    Thus, it is verified that Col. 7 is a unit hydrograph, containing 1 cm of runoff.

  2. For P = 20 cm, CN = 78, the runoff is Q = 13.4 cm.

  3. For P = 8 in, CN = 84, the runoff is Q = 6.1 in.

  4. From Table 4-6 of the San Diego County Hydtology Manual, the PZN's (AMC) are:  Coast: 2; Foothills: 3; Mountains: 3; Desert: 2.