Chelapati Example problem 1 (4.7.1)
You have been requested to compute the discharge for design of a bridge opening through a major highway. Flow records available at the site permit development of a unit hydrograph for the drainage area. It is therefore determined that the design discharge should be computed using the unit hydrograph technique. The information provided to you is as follows:
1. Drainage area upstream from bridge site = 43 sq miles
2. Flood hydrograph peak discharge = 9300 cfs
3. Flood hydrograph volume = 3260 acre-ft
4. Duration of runoff-producing portions of storm that produced flood hydrograph = 2 hours. (This indicates that th enet rain occurred in 2 hours).
Required:
A. From the data furnished, computer 2-hr unit hydrograph peak discharge.
B. The criteria for determining the bridge opening has been established to be the flood produced by 2.5-in of runoff occuring over a 2-hr period of time from the 43 sq mile drainage area.
i. What is the design discharge?
ii. What is the design flood hydrograph volume?
A. Qpeak = 6550 cfs
B. i. Qdesign = 16,375 cfs
B. ii. Vdesign = 5,733 acre-ft
Post follow-up if you have any questions.
JR