Civil Engineering Hydrology
LabProject No. 4 – Hydrograph Analysis
1. (9
0
pts) 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) |
|||||||||
| 0 |
4.5 |
2 20 |
310 |
||||||||
| 0.5 |
30 |
20 |
5.0 |
1 70 |
2 50 |
||||||
| 1.0 |
1 60 |
70 |
5.5 |
120 |
|||||||
| 1.5 |
1 90 |
6.0 |
80 |
90 | |||||||
| 2.0 |
4 40 |
6.5 |
60 | 50 | |||||||
| 2.5 |
530 |
400 |
7.0 |
40 | |||||||
| 3.0 |
470 |
450 |
7.5 |
||||||||
|
3.5 |
380 |
420 |
8.0 |
||||||||
|
4.0 |
300 |
360 |
8.5 |
(a.) Using the (–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).
2. (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:
1. Your report should include:
· A title page including a descriptive title, e.g. Project 1: precipitation; the name of the course, the due date, your name
· A statement of problem/purpose: very simply language to descript the project purpose, PLEASE DO NOT COPY THE PROBLEM STATEMENT in the project file.
· A description of methods: Please include the equations as needed.
· Calculation & Tabulated data as needed: this section should include the answers to the questions proposed in the problem statement
· Summary and conclusions: Summarize what you learned and your conclusions to reflect the project purpose, and maybe include potential sources of error and any reason why you believe your results to be correct.
2. Your report should be completed using a computer.
3. If you are not a great writer, get someone to proofread your report before you turn it in. A spellchecker/dictionary is useful. Frequent grammatical errors and misspelling in your report will not be regarded favorably by the grader or future employers.
A watershed as indicated in Figure on the right is divided into two subareas A and B. The surface runoff from subareas A enters a channel at point 1 while the runoff from subarea B enters the channel at point 2. There is a reservoir located directly downstream of point 2. The outlet of the reservoir is labeled as point 3. Subarea A is undeveloped with a (-index of 0.8 in/hr while subarea B is a residential development with a (-index of 0.2 in/hr. Subarea A has a constant baseflow of 10cfs while the baseflow for subarea B is 20cfs.