Ind. Admin. Code tit. 327, r. 3-6-12 – Slope requirements for gravity sewers

Authority: IC 13-13-5; IC 13-14-8; IC 13-14-9; IC 13-15-1-2; IC 13-15-2-1; IC 13-18-2

Affected: IC 13-11-2; IC 13-15; IC 13-18

Sec. 12. (a) Gravity sewers, when flowing full, shall be designed and constructed with slopes that shall result in average flow velocities of not less than two (2) feet per second in accordance with the following:

Minimum Slopes
Pipe Diameter (inches)	Minimum Slope (percent)
8	0.40
10	0.28
12	0.22
14	0.17
15	0.15
16	0.14
18	0.12
21	0.10
24	0.08
27	0.067
30	0.058
33	0.052
36	0.046
39	0.041
42	0.037

(b) Oversized gravity sewers shall not be approved to justify using decreased slopes.

(c) The slope of a gravity sewer, between any two (2) manholes, shall be uniform across the distance from the outlet invert elevation of the upstream pipe and the inlet invert elevation of the downstream pipe.

(d) Gravity sewers shall be provided with anchors to protect against damage from impact and erosion in accordance with the following:

(1) Slopes greater than twenty percent (20%) shall be provided with anchors spaced no more than thirty-six (36) feet on center.
(2) Slopes greater than thirty-five percent (35%) shall be provided with anchors spaced no more than twenty-four (24) feet on center.
(3) Slopes greater than fifty percent (50%) shall be provided with anchors spaced no more than sixteen (16) feet on center.

(Water Pollution Control Division; 327 IAC 3-6-12; filed May 17, 1999, 12:11 p.m.: 22 IR 3092; errata filed May 20, 1999, 6:36 p.m.: 22 IR 3108; readopted filed Apr 11, 2005, 2:45 p.m.: 28 IR 2470; readopted filed Jun 15, 2011, 11:15 a.m.: 20110713-IR- 327110193BFA; readopted filed Jun 29, 2017, 9:34 a.m.: 20170726-IR-327170225BFA; readopted filed May 12, 2023, 1:07 p.m.: 20230607-IR-327230079BFA; readopted filed Oct 18, 2024, 1:57 p.m.: 20241113-IR-327230810RFA)