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Culvert Design Problem 1 - Determine culvert pipe size for discharge conditions:
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Size a concrete culvert pipe crossing under a county road for the following design conditions: Q = 35 cfs; maximum headwater elevation is 104.6; upstream flowline elevation is 100.1; downstream flowline elevation is 99.7; culvert length is 58 ft and the culvert will project from fill with no headwalls. |
1. The problem states that the maximum headwater elevation is 104.6' and the upstream flowline elevation is 100.1. Thus the maximum headwater depth is 104.6 - 100.1 = 4.5'. Now, from the culverts submenu open the round trial design culvert selection calculation, CulvertSelRnd.aspx. Input the "Title" of the calculation, the "Designer/Checker" information and the variables.
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2.
From the culverts submenu open up the inlet control culvert submerged inlet calculation, CulverICS.aspx. Input the "Title" of the calculation, the "Designer/Checker" information and the variables.
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3. Open up the reference tables and find the inlet control constants "c" and "Y" from the table.
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4.
Input the remaining variable and click on the "Calculate" button. Read the results. The inlet control headwater depth is 2.835 ft.
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5.
Next open up the outlet control round culvert calculation, CulvertRndOC.aspx. Input the "Title" of the calculation, the "Designer/Checker" information and the variables.
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6.
Open up the reference tables and find the entrance loss conefficient, "Ke" and the value for Manning's roughness coefficient "n".
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7.
Enter the remaining variables and click on the "Calculate" button. Read the results. The outlet control culvert head is 0.248 ft.
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8.
From the culverts submenu open up the tailwater depth calculation, Culvertho.aspx. Input the "Title" of the calculation, the "Designer/Checker" information and the variables.
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9.
Open up the critical depth charts and determine the critical depth of a round 3.5' culvert flowing 35 cfs.
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10.
Enter the critical depth and click on the "Calculate" button. Read the results. The tailwater depth, ho is 2.60 ft.
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11.
From the culverts submenu open up the headwater outlet control culvert calculation, CulvertHWOC.aspx. Input the "Title" of the calculation, the "Designer/Checker" information and the variables. Click on the
"Calculate" button and read the results. The headwater depth for a round pipe culvert under outlet control is 2.442 ft.
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12.
From the culverts submenu open up the culvert outlet velocity calculation, CulvertVout.aspx. Input the "Title" of the calculation, the "Designer/Checker" information and the variables. Click on the
"Calculate" button and read the results. The outlet velocity is 3.638 fps.
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13. Summary
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Use a 42 inch concrete culvert pipe. Assume the culvert pipe is under inlet control with a headwater depth of 2.835 ft. Since the outlet velocity is 3.638 fps which is greater than scour velocity of 2 fps, provide erosion protection at the outlet for a minimum distance into the stream channel to prevent erosion.
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