“TINHORN CULVERT CORRUGATED METAL PIPE PLASTIC STEEL”
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In the picture above, we replaced a single 36″ cmp with 1-36″ n-12 and 2-30″ n-12 on 2% grade, and increased the flow 5X!
| 2025 FLOW CHART | GPM’S | GPM’S | GPM’S | |||||
| pcs | Dia. | CMP | Grade .01% | Grade 1.5% | C.F.S. @ 1.5% | Grade 2% | C.F.S. @ 2% | Grade 2.5 % |
| n-12 DW | 20′ = 0″ | 20′ = 3.6″ | 20′ = 4.8″ | 20′ = 6″ | ||||
| 1 | 8″
10″ 12″ |
cmp | 47 gpm
78 gpm 123 gpm |
1500 gpm | 3.34 | 677 gpm
1507 gpm 1733 gpm |
3.86 | 1938 gpm |
| 1 | 8″
10″ 12″ |
n-12 | 60 gpm
108 gpm 173 gpm |
2125 gpm | 4.74 | 833 gpm
1607 gpm 2455 gpm |
5.47 | 2745 gpm |
| 1 | 15″ | cmp | 187 gpm | 2312 gpm | 5.15 | 2676 gpm | 5.96 | 2989 gpm |
| 1 | 15″ | n-12 | 314 gpm | 3859 gpm | 8.6 | 4454 gpm | 9.92 | 4982 gpm |
| 1 | 18″ | cmp | 309 gpm | 3758 gpm | 8.37 | 4344 gpm | 9.68 | 4851 gpm |
| 1 | 18″ | n-12 | 515 gpm | 6271 gpm | 14 | 7238 gpm | 16.13 | 8094 gpm |
| 1 | 21″ | cmp | 464 gpm | 5676 gpm | 12.65 | 6550 gpm | 14.59 | 7227 gpm |
| 1 | 24″ | cmp | 663 gpm | 8104 gpm | 18 | 9358 gpm | 20.85 | 10457 gpm |
| 1 | 24″ | n-12 | 1099 gpm | 13501 gpm | 30 | 15587 gpm | 34.73 | 17419 gpm |
| 1 | 30″ | cmp | 1189 gpm | 14688 gpm | 32.73 | 16956 gpm | 37.78 | 18960 gpm |
| 1 | 30″ | n-12 | 2004 gpm | 24465 gpm | 54.51 | 28253 gpm | 62.95 | 31600 gpm |
| 1 | 36″ | cmp | 1934 gpm | 23877 gpm | 53 | 27587 gpm | 61 | 30822 gpm |
| 1 | 36″ | n-12 | 3234 gpm | 39796 gpm | 89 | 45947 gpm | 102 | 51370 gpm |
| 1 | 42″ | cmp | 2935 gpm | 36039 gpm | 80.3 | 41607 gpm | 92.7 | 46527 gpm |
| 1 | 42″ | n-12 | 4921 gpm | 60036 gpm | 133.76 | 69316 gpm | 154.44 | 77517 gpm |
| 1 | 48″ | cmp | 4228 gpm | 51412 gpm | 114.55 | 59417 gpm | 132.38 | 66407 gpm |
| 1 | 48″ | n-12 | 6990 gpm | 85743 gpm | 191 | 98991 gpm | 220.55 | 110660 gpm |
| 1 | 60″ | cmp | 7575 gpm | 93280 gpm | 207.83 | 107726 gpm | 240 | 120409 gpm |
| 1 | 60″ | n-12 | 12684 gpm | 155466 gpm | 346.38 | 179513 gpm | 400 | 200653 gpm |
| 1 | 72″ | cmp | 12430 gpm | 151700 gpm | 338 | 175165 gpm | 390 | 195840 gpm |
| 1 | 84″ | cmp | 18645 gpm | 228751 gpm | 510 | 264143 gpm | 588 | 295391 gpm |
| 1 | 96″ | cmp | 26608 gpm | 326738 gpm | 728 | 377248 gpm | 840 | 421670 gpm |
| 1
1 |
102″
108″ |
cmp
cmp |
31,311 gpm
36530 gpm |
542,976 gpm @ 3%
447204 gpm |
996 |
586,505 gpm @ 3.5%
516553 gpm |
1151 |
495,627 gpm
577341 gpm |
| 1 | 120″ | cmp | 48269 gpm | 592269 gpm | 1320 | 683875 gpm | 1524 | 764560 gpm |
Legend:
1. cmp = corrugated metal pipe, requires 2.5% minimum grade for proper installation.
2. cmp is spiral wound, when the water flows on proper minimum grade, it will sweep the cmp clean of sediment each time.
If cmp is not installed on proper minimum grade, the sediment can build up and eventually deteriorate the cmp from the inside.
The green flow numbers above represent control, if you don’t understand, call before wasting time, effort and crown.
3. n-12DW = n-12 double wall polyethylene pipe, n-12’s recommended minimum grade is “2%”.
4. gpm = gallons per minute.
5. c.f.s. = cubic feet per second.
6. Head is the “inlet side”.
7. Tail is the “outlet side”.
8. “Grade” grade is the amount of fall or drop from one end of the pipe to the other end of the pipe’
A. How important is setting the pipe on the proper grade?
1. * 2.5% grade over 20’= 6″ minimum requirement for proper cmp installation and maximum performance.
2. * 2% grade over 20’= 4.8″ or about 4-3/4″ minimum requirement for proper n-12 installation.
3. * 1.5% grade over 20’= 3.6″ or a little over 3-1/2″, improper for all installations.
9. Compare the volume (gpm) between 0.01% (control) grade vs. the recommended grade to see the resulting differences.
10. The use of good judgement and caution is advised, the more you increase the grade the more the water will “dig” on the tail side.
11. In the picture above, we replaced a single 36″ cmp with 1-36″ n-12 and 2-30″ n-12 on 2% grade, and increased the flow 5X!
12. Please use the flow chart tool to take advantage of the potential to install your pipe for maximum performance.
Note: Maximum performance results from proper installation, which requires setting the pipe at least to the minimum recommended grade. SEE FLOW CHART
Note 2: You can increase flow performance by elevating the grade to a higher %, for example a 72″ cmp picks up 19,500 gpm from 195,840 on 2.5% grade to 214,500 gpm on 3% grade, with the additional 1/2% grade from 2.5% to 3%, amounts to a 10% increase in gpm’s (flow).
“TINHORN CULVERT CORRUGATED METAL PIPE PLASTIC STEEL”