Idaho Administrative Code › Title IDAPA 37 - Water Resources, Department of › Rule 37.03.07 - STREAM CHANNEL ALTERATION RULES › Section 37.03.07.057 - DUMPED ROCK RIPRAP

Current through August 31, 2023
01.
Placement of Riprap
. Riprap shall be placed on a granular bedding
			 material or a compact and stable embankment. (3-18-22)
02.
Sideslopes of Riprap
.
			 Sideslopes of riprap shall not be steeper than 2:1 (2' horizontal to 1'
			 vertical) except at ends of culverts and at bridge approaches where a 1 1/2:1
			 sideslope is standard. (3-18-22)
03.
Minimum Thickness of Riprap
.
			 The minimum thickness of the riprap layer shall equal the dimension of the
			 largest size riprap rock used or be eighteen (18) inches, whichever is greater.
			 When riprap will be placed below high water level, the thickness of the layer
			 shall be fifty percent (50%) greater than specified below. (3-18-22)
04.
Riprap Protection
. Riprap
			 protection must extend at least one (1) foot above the anticipated high water
			 surface elevation in the stream. (3-18-22)
05.
Rock Used for Riprap
. Rock
			 for riprap shall consist of sound, dense, durable, angular rock fragments,
			 resistant to weathering and free from large quantities of soil, shale, and
			 organic matter. The length of a rock shall not be more than three (3) times its
			 width or thickness. Rounded cobbles, boulders, and streambed gravels are not
			 acceptable as dumped riprap. (3-18-22)
06.
Size and Gradation of
			 Riprap
. Riprap size and gradation are commonly determined in terms of
			 the weight of riprap rock. The average size of riprap rock shall be at least as
			 large as the maximum size rock that the stream is capable of moving. The
			 maximum size of riprap rock used shall be two (2) to five (5) times larger than
			 the average size. (3-18-22)
07.
Methods Used for Determining Gradation of Riprap
. There are many
			 methods used for determining the gradation of riprap rock. One of these many
			 acceptable methods is shown in Table 1 below. Another acceptable method is the
			 Far West States (FWS) method shown in APPENDIX A - Table 1A.
Table 1 - GRADATION OF RIPRAP IN
							 POUNDS
Max. Weight of Stone required
							 (lbs)
Min. and Max. Range in weight of
							 Stones (lbs)
Weight Range 75 percent of Stones
							 (lbs)
150
25 - 150
50 - 150
200
25 - 200
50 - 200
250
25 - 250
50 - 250
400
25 - 400
100 - 400
600
25 - 600
150 - 600
800
25 - 800
200 - 800
1000
50 - 1000
250 - 1000
1300
50 - 1300
325 - 1300
1600
50 - 1600
400 - 1600
2000
75 - 2000
600 - 2000
2700
100 - 2700
800 - 2700
(3-18-22)
08.
Use of Filter Material
. A
			 blanket of granular filter material or filter fabric shall be placed between
			 the riprap layer and the bank in all cases where the bank is composed of
			 erodible material that may be washed out from between the riprap rock. Filter
			 material shall consist of a layer of well-graded gravel and coarse sand at
			 least six (6) inches thick. (3-18-22)
09.
Toe Protection
. Some
			 suitable form of toe protection shall be provided for riprap located on
			 erodible streambed material. (3-18-22)
a.
			 Various acceptable methods of providing toe protection are shown in APPENDIX B,
			 Figure 2 at the end of this chapter. (3-18-22)
b. In addition to the approved methods of
			 providing toe protection as shown in APPENDIX B, any other reasonable method
			 will be considered by the Director during review of a proposed project.
			 (3-18-22)