Section 320.07. Culvert area calculation, culvert sizing, and culvert length determination.

  Applicants shall use the following calculation and assessment methods:

(1)   Calculation of required culvert area. To determine the required culvert area, 3 measurements shall be made: channel width of the stream in feet at the ordinary high water mark (W 1 ), channel width of the stream in feet at the stream bottom (W 2 ), and the height in feet of the high water above the stream bottom (H) (see diagram). These 3 measurements shall be made at each of 3 locations or transects along the stream: the location of the proposed crossing, 100 feet upstream from the crossing, and 100 feet downstream from the crossing. The individual measurements of W 1 , W 2 and H shall be averaged to derive the final W 1 , W 2 and H values. The required culvert area is then calculated with the following equation:

Required Culvert area (square feet) = H x (W 1 + W 2 )

- See PDF for diagram

(2)   Culvert sizing . Once the required culvert area has been determined, the applicant can identify the proper culvert size by reviewing the following tables. The minimum size culvert needed to pass flows must have an area that is as much or more than the required culvert area. For example, the recommended culvert size for a culvert area calculation of 8.50 square feet would be 42 ‶ .

Table 1. Round culvert diameters and corresponding culvert area.

Culvert diameter (in.)   Culvert area (sq. ft.)

  18   1.80

  24   3.10

  30   4.90

  36   7.10

  42   9.60

  48   12.60

  54   15.90

  60   19.60

  66   23.80

(3)   Culvert length determination. The proper culvert length is determined by the following calculation:

CR 04-084 : cr. Register April 2005 No. 592 , eff. 5-1-05.

Note

To find the area of any round culvert, use the following equation: Microsoft Windows NT 6.1.7601 Service Pack 1 Culvert diameter (in.) divided by 2 = _____ divided by 12 = _____ (radius in ft.) Microsoft Windows NT 6.1.7601 Service Pack 1 Radius x Radius x 3.14 = _________ (area of culvert in sq. ft.) Microsoft Windows NT 6.1.7601 Service Pack 1 Table 2. Pipe arch dimensions and corresponding culvert area. Microsoft Windows NT 6.1.7601 Service Pack 1 Pipe width or span (in.) Pipe height or rise (in.) Culvert area (sq. ft.) Microsoft Windows NT 6.1.7601 Service Pack 1   43   27   6.4 Microsoft Windows NT 6.1.7601 Service Pack 1   50   31   8.7 Microsoft Windows NT 6.1.7601 Service Pack 1   58   36   11.4 Microsoft Windows NT 6.1.7601 Service Pack 1   65   40   14.3 Microsoft Windows NT 6.1.7601 Service Pack 1   72   44   17.6 Microsoft Windows NT 6.1.7601 Service Pack 1   73   55   22.0 Microsoft Windows NT 6.1.7601 Service Pack 1   85   54   25.3 Microsoft Windows NT 6.1.7601 Service Pack 1   81   59   26 Microsoft Windows NT 6.1.7601 Service Pack 1   87   63   31 Microsoft Windows NT 6.1.7601 Service Pack 1   95   67   35 Microsoft Windows NT 6.1.7601 Service Pack 1   103   71   40 Microsoft Windows NT 6.1.7601 Service Pack 1 - See PDF for diagram Microsoft Windows NT 6.1.7601 Service Pack 1