CE445-APPLIED HYDROLOGY
FALL 2001
SECOND MIDTERM
NOVEMBER 20, 2001, 0930-1045

Name: ______________________ S.S. No. ________________ Grade: _______

Instructions: Open book only. Use engineering paper. When you are finished, staple your work in sequence (1 to 4), and return this sheet with your work.

  1. (25%) Rain falls on a 300-ha composite catchment which drains two subareas, as follows: (1) subarea A, steep, draining 20%, with time of concentration 10 min and C = 0.8; and (2) subarea B, milder steeper, draining 80%, with time of concentration 60 min and C = 0.4. Calculate the peak flow corresponding to the 25-yr frequency. Use the following IDF function:
    I = 800 T0.2 / (tr + 15)0.7
    in which I = rainfall intensity in mm/hr, T = return period in yr, and tr = rainfall duration in min. Assume linear flow concentration at the catchment outlet.

  2. (25%) A certain basin has the following 3-hr unit hydrograph (1 cm of rainfall):

    Time (hr)         0 03 06 09 12 15 18 21 24

    Flow (m3/s):   0 10 20 30 25 20 15 10  0

    Calculate the composite flood hydrograph for the following storm pattern:

    Time (hr)                            0   03   06   09   12

    Total rainfall (mm/hr):        06   10    18   02

    The CN= 80.

  3. (20%) Given the following statistics of annual maxima for the Clearwater River: number of years n = 35; mean = 3545 cfs; standard deviation = 1870 cfs. Calculate the 100-yr flood discharge using the Gumbel method.

  4. (30%) Please answer briefly:

    (a) Why is the rational method rational?
    (b) Why is the runoff curve number method conceptual?
    (c) What are the differences between the Snyder and SCS synthetic unit hydrographs?
    (d) How does the TR-55 method account for runoff diffusion?
    (e) For what value of skew coefficient does the Log Pearson III method plot as a straight line on log-probability paper?
    (f) What is the correlation coefficient if the x-y data depicts a perfect circle?