Idaho Administrative Code › Title IDAPA 20 - Lands, Department of › Rule 20.02.01 - RULES PERTAINING TO THE IDAHO FOREST PRACTICES ACT › Section 20.02.01.040 - ROAD CONSTRUCTION, RECONSTRUCTION AND MAINTENANCE

Current through August 31, 2023
01.
Purpose
. Provide standards and guidelines for road construction, reconstruction, and maintenance that will maintain forest productivity, water quality, and fish and wildlife habitat. (3-31-22)
02.
Road Specifications and Plans
. Road specifications and plans must be consistent with good safety practices. Landowners and Operators should plan each road to the minimum use standards adapted to the terrain and soil materials to minimize disturbances and damage to forest productivity, water quality, fish, and wildlife habitat. In addition, landowners and operators must: (3-31-22)
a. Plan transportation networks to avoid road construction within SPZs, except at approaches to stream crossings. Leave or reestablish areas of vegetation between roads and streams. (3-31-22)
b. Plan roads no wider than necessary to safely accommodate the anticipated use. Minimize cut and fill volumes by aligning the road to fit the natural terrain features as closely as possible. Adequately compact fill material. Dispose of excess material on geologically stable sites. (3-31-22)
c. Plan roads to drain naturally by out-sloping or in-sloping with cross-drainage and by grade changes where possible. Install dips, water bars, cross-drainage, or subsurface drainage on roads when necessary. (3-31-22)
d. When natural drainage will not protect the surface, cut slopes or fill slopes, plan roads with relief culverts and roadside ditches. Install culverts to prevent erosion of the fill by properly sizing, bedding and compacting. Ensure drainage structures avoid direct discharge of sediment into streams. (3-31-22)
e. This rule applies to new culvert installations, or reinstallations during road reconstructions or because of catastrophic events. Temporary culvert crossings are exempt from the fifty (50) year peak flow design requirement but must be removed before seasonal run-off. (3-31-22)
i. Culverts in fish-bearing streams must provide for fish passage. (3-31-22)
ii. Design stream crossings to carry the fifty (50) year peak flow using Department accepted engineering methods or the culvert sizing table below. Armor the inlet or use a flared inlet structure on thirty (30) inch or greater diameter culverts. The minimum diameter culvert allowed is eighteen (18) inches.
CULVERT SIZING TABLE
The left side of this culvert sizing table will be used for the area of the state north of the Salmon River and within the South Fork Salmon River drainage; the right side will be used for the area of the state south of the Salmon River and outside the South Fork Salmon River drainage. It was developed to carry the fifty (50) year peak flow at a headwater-to-diameter ratio of one (1).
North Forest Region and South Fork Salmon River Drainage
South Forest Region
Watershed Area (acres)
Required Culvert Diameter (inches)
Culvert Capacity (in cubic feet/sec)
Watershed Area (acres)
Ditch relief, seeps, springs, wet areas, draws
12
NA
Ditch relief, seeps, springs, wet areas, draws
less than 32
18
6
Less than 72
33 - 74
24
12
73-150
75 - 141
30
20
151-270
142 - 240
36
32
271-460
241 - 366
42
46
461-720
367 - 546
48
65
471-1025
547 - 787
54
89
1026-1450
788 - 1027
60
112
1451-1870
1028 - 1354
66
142
1871-2415
1355 - 1736
72
176
2416-3355
1737 - 2731
84
260
3356-5335
2732 - 4111
96
370
5336-7410
4112 - 5830
108
500
7411-9565
5831 - 8256
120
675
9566-11780
Culverts larger than one hundred twenty (120) inches must be designed; consider alternative structures. (3-31-22)
iii. Relief culverts, and those used for seeps, springs, wet areas, and draws must not be less than twelve (12) inches in diameter for permanent installations. (3-31-22)
f. On existing roads that are not reconstructed or damaged by catastrophic events, landowners or operators are encouraged, but not required, to replace or provide mitigation for culverts that do not provide for fish passage in accordance with Subparagraph 040.02.e.i. or cannot carry the fifty (50) year peak flow of Subparagraph 040.02.e.ii. (3-31-22)
g. Plan and install stream crossings in compliance with the Stream Channel Protection Act (Title 42, Chapter 38, Idaho Code), Paragraph 030.07.b. and the culvert sizing requirements of Paragraph 040.02.e. Fords are acceptable stream crossing structures on small, shallow streams, with gradients less than four percent (4%). For fords: cross-drain and rock the road surface on each side of the stream for at least seventy-five (75) feet for Class I and at least thirty (30) feet for Class II streams; minimize sediment delivery to streams by limiting use to low water, dry, or frozen conditions; minimize hauling or equipment crossing trips during times of salmonid spawning and egg incubation. (3-31-22)
h. Avoid reconstruction of existing roads located in SPZs, except for approaches to stream crossings, unless it will result in the least long-term impact on site productivity, water quality, and fish and wildlife habitat. Reconstruction of existing roads in SPZs requires a variance. Reusing existing roads in SPZs for skidding or landing logs requires a variance. Reusing existing roads in SPZs only for hauling fully suspended logs does not require a variance. (3-31-22)