_INSPECTION - C1982057 ‎(67)‎

• Permit No: C1982057
• IBM Index Class Name: INSPECTION
• Doc Name: Inspection Report
• Inspection Date: 5/26/2009
• Email Name: DTM
• Media Type: D
• Archive: No

Permanent Channel Erosion
Extensive permanent channel repairs will be necessary in the 016 watershed, which appears to have been
subject to a high intensity rainfall event over the weekend of May 23-26. Numerous channel repair locations are
delineated in this watershed on the 2009 R&G map. Permanent channel repair locations are also properly noted
in various other locations on the map.
The operator had recently initiated rill and gully and channel repairs, but progress was delayed and set back by
the recent rainfall, and associated erosion and muddy conditions.
005 Gulch "Minimal Disturbance"Drainage Segment
During the inspection, a segment of the 005 drainage channel in the northern part of the permit area was
walked. The channel segment is downstream from the"D" Pit reclaimed spoils, and the specific section
inspected extends from the riprapped outlet of Stock Pond T-20 at the upper end, down to a riprapped segment
just above Stock Pond T-22 at the lower end. The segment was not directly disturbed by mining, but disturbed
area runoff from the reclaimed "D" Pit area flows through the channel to Sediment Pond 005, lower in the
watershed. Stabilization grading and riprap installation has been conducted along certain reaches of the channel
subject to erosive flows in the past. The following excerpt is from a DRMS inspection report dated August 7,
2007, describing observations made on an inspection of July 31, 2007.
A couple of permit designated"minimal disturbance"native drainage channels were walked
during the inspection...The 005 drainage is deeply incised along most of its length, and
inspection several years ago had noted indications of recent down-cutting in several locations.
At present, the channel appears to be relatively stable, and vegetation is becoming established
along and within the channel along most of its length;likely due to maturing vegetation cover
and reduced runoff from the reclaimed`D"pit portions of the watershed. There is:some
apparently recent minor down-cutting along a 150 foot segment toward the lower end of the
reach, immediately upstream of the point where a riprapped road outlet drain enters the
channel. Stabilization measures may be warranted along this segment prior to sediment
pond removal, if it does not stabilize within the next few years. There is a heavy
infestation of Canada thistle along the drainage within the minimal disturbance area and
spraying is warranted.
Photos#1 through#8, attached to this report, provide comparison of particular channel reaches as they
appeared in July 2007 and in May 2009. The photo sequence progresses in an upstream direction along the
segment. The photos do not provide exactly the same"repeat photography' perspective in each case, but do
depict the same approximate locations. Photos 1 and 2 show the lower reach, immediately upstream of the
riprapped road ditch downdrain; the channel has not cut deeply through this segment since 2007, but there has
been recent scour and the segment does not appear to be healing. Grasses are becoming established along
the banks, where Canada thistle previously dominated.
Photos 3 and 4 are of an incised segment immediately downstream from a pasture fence. There appears to
have been recent bank erosion and sloughing along this reach. Photos 5 and 6 show the channel segment at
the pasture fence crossing. There appears to have been further scour along this reach, and the headcut
associated with the incised segment shown in#3 and#4 appears to have progressed upstream. Photo#7
depicts an apparently stable, grass lined reach of channel in 2007, which is the site of an active headcut and
side-slope sloughing in 2009(Photo#8).
On the 2009 Rill and Gully map, the operator has indicated a proposed drop structure, to be located in the
approximate location of the active headcutting depicted on Photo#8. The Division concurs that measures are
warranted in this location to prevent progression of the headcut and associated bank slouglhage and erosion
(armored drop structure or a riprapped grade transition zone). Similar measures would appeared to be
warranted for the headcut at the fence crossing, (and other potentially unstable nickpoints, if they occur
along the segment). Low keyed check structures would appear to be warranted along the scoured
section depicted in Photo#2, to reduce flow velocities and minimize further incision.
5