Hydrograph Analysis-Civil Engineering Hydrology

Lab Project No. 4 – Hydrograph Analysis

1. (90pts) The following storm occurs over the watershed:

Time (hr)                                                 0.5        1.0        1.5         2.0        2.5
Accumulative rainfall depth (inch)          0.5        1.2        2.0         3.0        3.2

The following unit hydrographs are given for subareas A and B.

 Time   (hr) Subarea A, 2-hr unit hydrograph, (cfs/in) Subarea B, 0.5-hr unit hydrograph, (cfs/in) Time   (hr) Subarea A, 2-hr unit hydrograph, (cfs/in) Subarea B, 0.5-hr unit hydrograph, (cfs/in) 0 0 0 4.5 220 310 0.5 30 20 5.0 170 250 1.0 160 70 5.5 120 160 1.5 310 190 6.0 80 90 2.0 440 310 6.5 60 50 2.5 530 400 7.0 40 20 3.0 470 450 7.5 30 0 3.5 380 420 8.0 20 0 4.0 300 360 8.5 0 0

(a.) Using the f–index values, determine the excess rainfall over each subarea for the storm for each half-hour period (10).
(b.) Compute the half–hour unit hydrograph for subarea A from the 2-hr unit hydrograph by using the S-hydrograph method (20).  On the same graph, show the S-hydrograph, and the half- hour and 2-hr unit hydrographs (5).  A table in your discussion should summarize the peak flow rate, time to peak, and time base of both the half- hour and 2-hr unit hydrographs for subarea A (5).
(c.) For the storm above, calculate the direct runoff hydrographs and the streamflow hydrographs for both subareas (30).  On the same graph, show both hydrographs for both subareas (5).  A table in your discussion should summarize the peak flow rate, time to peak, and time base for the direct runoff and streamflow hydrographs (5).
(d) Calculate the drainage area (in both acres and mi2) for each of the subarea (10).

1. (10pts) Format and quality of your report.

As you work to complete your reports, pretend you are a practicing engineer or hydrologist and the report is to be submitted to your supervisor and /or a client. Sloppy, disorganized and /or inaccurate work is likely to get you fired. Here are some basic guidelines: