HOMEWORK SET 6

 

CTC 260 Hydrology

 

Hydrograph Synthesis

 

 

 

A measurement station on a stream after a 2-hour storm recorded the following discharges from a 1.2 square mile drainage area

 

Hour	Discharge (cfs)
0	102
1	99
2	101
3	215
4	507
5	625
6	455
7	325
8	205
9	145
10	100
11	70
12	55
13	49
14	43
15	38

 

Develop a 2-hour Unit Hydrograph

 

a)     Develop the runoff hydrograph by separating the groundwater from the discharge by a straight (or sloped line) 

b)     Develop the unit hydrograph

Hint #1:  Flow should start and end at zero cfs

Hint #2: The area under the unit hydrograph (in cubic feet) should equal 1” times the drainage area (in cubic feet)

c)     Graph the following on one graph (x-axis time: 0 to 15 hours)

• Discharge data
• Baseflow
• Runoff hydrograph
• Unit hydrograph (2-hour)

 

 

Synthesize Unit Hydrographs (Lagging Storm & S-Curve Methods)

 

a)     Synthesize and graph a 4-hour unit hydrograph using the lagging storm method

b)     Synthesize and graph a 1-hour unit hydrograph using the S-curve method. 

 

Graph Unit Hydrographs

 

On the same graph and using the same time increments (0-15 hours), graph the 1-hour, 2-hour, and 4-hour unit hydrographs.  What is true about the area under the graphs?  How do the peak flows and time to peak flows compare to each other?