Problems
- As part of a major development, a stream crossing must be constructed at river mile 14.785 of the lower reach of the East Grand Fork River, which is shown in the figure.
- What is the computed water surface elevation at river mile 14.43?
- What is the average velocity in the main channel at river mile 15.73?
- How much head loss due to friction occurs between river mile 13.86 and 13.98?
- What are the left overbank, main channel, and right overbank conveyances at river mile 14.43?
- What is the energy grade elevation at river mile 13.03?
- What is the energy correction factor (a) at river mile 14.79?
- English units - Add the data describing the proposed bridge at river mile 14.785 to the channel reach from problem 6.1. The roadway deck elevation of the crossing will be 462.0 ft, and the low chord elevation will be 459.0 ft along the entire length of the bridge. The roadway deck will be 48 ft wide, and the distance from the deck to the upstream cross section should be taken as 1 ft. A weir coefficient of 2.6 should be used.
- The agency responsible for floodplain management has stressed that the stream crossing from problem 6.2 must not cause any adverse affects to the hydraulics of the stream system. Perform analyses using each the following bridge modeling approaches and record the results in the table provided.
- Energy method
- Momentum method option
- Yarnell's equation
- The agency responsible for floodplain management of the stream has asked you to design a structure that produces no increase in the water surface elevation upstream of the bridge. Do you believe this is possible? If so, how might it be accomplished?
English Units - Cross-section geometry data for the reach without the proposed bridge is provided in the file Prob6_1eng.g01 on the CD-ROM accompanying this text. The channel discharge for the 100-year storm event between river miles 14.43 and 16.16 is 25,660 ft3/s. A tributary adds 3290 ft3/s at river mile 14.13. The flow regime is subcritical, and the starting water surface elevation at river mile 12.59 is 450.00 ft. For the existing condition (no bridge), answer the following questions.
SI Units - Cross-section geometry data for the reach without the proposed bridge is provided in the file Prob6_1si.g01 on the CD-ROM accompanying this text. The channel discharge for the 100-year storm event between river miles 14.43 and 16.16 is 726.7 m3/s. A tributary adds 93.2 m3/s at river mile 14.13. The flow regime is subcritical, and the starting water surface elevation at river mile 12.59 is 137.2 m. For the existing condition (no bridge), answer the questions above.
Two 5 ft diameter circular piers will be used to support the structure, and they will be located at cross-section stations 320.0 ft and 433.0 ft. The structure will also have sloping abutments, which are described by the data in the following table. Assume that the bridge geometry is the same for the upstream and downstream ends of the structure.
|
Left Abutment
|
Right Abutment
|
||
|---|---|---|---|
|
Station, ft
|
Elevation, ft
|
Station, ft
|
Elevation, ft
|
|
0
|
459
|
480
|
446
|
|
250
|
459
|
519
|
459
|
|
277
|
450
|
800
|
459
|
SI units - Add the data describing the proposed bridge at river mile 14.785 to the channel reach from problem 6.1. The roadway deck elevation of the crossing will be 140.8 m, and the low chord elevation will be 139.9 m along the entire length of the bridge. The roadway deck will be 14.6 m wide, and the distance from the deck to the upstream cross section should be taken as 0.3 m. A weir coefficient of 1.44 should be used.
Two 1.5 m diameter circular piers will be used to support the structure, and they will be located at cross-section stations 97.5 m and 132.0 m. The structure will also have sloping abutments, which are described by the data in the following table. Assume that the bridge geometry is the same for the upstream and downstream ends of the structure.
|
Left Abutment
|
Right Abutment
|
||
|---|---|---|---|
|
Station, m
|
Elevation, m
|
Station, m
|
Elevation, m
|
|
0.0
|
139.9
|
146.3
|
135.9
|
|
76.2
|
139.9
|
158.2
|
139.9
|
|
84.4
|
137.2
|
243.8
|
139.9
|
Left and right ineffective flow area boundaries must be defined for the cross sections immediately upstream and downstream of the bridge. It is recommended that the initial elevation of the upstream ineffective flow areas be taken as equal to the low point of the road, and the initial elevation of the downstream ineffective flow areas be taken as equal to the low chord elevation. Complete the worksheet below to select the stationing for the upstream and downstream encroachments assuming a 1:1 contraction ratio and a 3:1 expansion ratio. If there is a significant difference between assumed water surface elevations and computed water surface elevations (and thus a significant difference in top width of flow due to the sloping abutments), multiple iterations may be required to arrive at final encroachment stations.
