INSPEC13634

• Permit No: C1981041
• IBM Index Class Name: Inspection
• Doc Name: Inspection Report
• Inspection Date: 8/9/2006
• Media Type: D
• Archive: No

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The inlet end of the Coal Gulch Culvert beneath Haul Road 4 (Coal Canyon Road) was approximately Yz
filled with sediment, and will need to be cleaned out to restore design capacity. The culvert may need to
be re-set at a higher grade to prevent sediment accumulation in the culvert following flow events.
Photo 2716 is a view of the CRDA-2 West Upper Diversion outlet erosion from below. This erosion was
described in the previous inspection report, and photos associated with that inspection were taken from the ditch
outlet with view down the slope from above.
The next stream segment walked was further downstream, between the permitted "upper dip section" crossing
(6 culverts imbedded in a concrete low water crossing structure) and the 2nd permitted crossing (large Haul Road
4 fill embankment with two 81 "x59" CMP culverts). This segment of the stream is a permitted stream channel
diversion, which passes to the left of Sediment Pond 6 immediately downstream of the upper dip section, and to
the right of Sediment Pond 10, midway between the upper dip section and the 2nd Haul Road 4 crossing. Photo
2797 is a view downstream along the channel toward the upper dip section. Track hoe work had already been
initiated along the Coal Creek diversion segment, working downstream from the dip section. Culvert inlet area
had been excavated and bank and channel erosion immediately downstream and along the sides of the
concrete structure had been backfilled and riprapped. Further downstream there were areas of deep gouges in
the channel where flow had apparently dislodged large boulders and subsequently eroded, and there were areas
of significant bank erosion and sediment deposition. Bank erosion was most pronounced along the left bank
adjacent to the Pond 10 embankment, which had previously been riprapped. The riprap had been washed out
and the bank eroded. At the location where the Pond 10 primary discharge pipe extends through the
embankment to the edge of the channel, the channel bottom was approximately 7.5 feet to 8 feet lower than the
bottom of the pipe; prior to the August 1 flow event, this distance had been measured at 5 feet. At the lower end
of the segment, the stream had built up at the road embankment, washed over the road, and backed up into the
reclaimed soil borrow area CBA-1, which is located adjacent to the right bank of the channel. Thick deposits of
sediment and rock were deposited upstream from the road embankment for a distance of several hundred feet.
Photos 2718 through 2727 are of the segment between the Upper Dip Section and the lower Haul Road 4
crossing of Coal Creek.
The CBA-1 small area exemption sediment control sump had been inundated and was stilt mostly full of water
and an unknown quantity of sediment. The Road outlet ditch adjacent to the sump was completely filled in with
sediment. The downstream side of the road embankment where the stream poured over the road across a wide
swath was heavily eroded. See Photos 2728, and 2730 through 2735.
Maintenance work along this segment of the channel had begun prior to the inspection and was
continuing. Channel grading and excavation work will be necessary to restore the design channel
gradient and cross section. Bank erosion along the Pond 10 embankment will need to be repaired and
riprap replaced. The CBA-1, SAE sump will need to be excavated and restored to design when it dries
sufficiently, adjacent road outlet ditch will need to be cleaned out, and the eroded downstream slope of
the Haul Road 4 embankment will need to be repaired and stabilized. A significant volume of material
suitable for use as refuse cover or for other reclamation purposes may be recovered from channel,
ditch, and pond maintenance. The material will need to be placed in an appropriate, sediment controlled
location, where it can be stored, stabilized, and will remain undisturbed until it is used for reclamation,
The segment of channel from the large double culverts beneath the road embankment down to the riprap
transition structure near the Sediment Pond 13 spillway outlet held up well, with no significant deposition or
scour. The riprap transition structure itself functioned well and was in good condition. See Photos 2729, 2736,
and 2737.
The final disturbed area segment of the Coal Creek channel is further ddwnstream, where the UTL Haul Road
crosses the channel, at another 6 culvert concrete low water crossing (the "Lower Dip Section'). Flood flows had
poured over the concrete structure, and channel banks and fill along the sides and beneath a portion of the
concrete had been eroded. See Photos 2738 through 2744. Erosion will need to be repaired and large
riprap replaced to protect channel banks downstream of the structure. Five of the 6 culverts were
blocked and need to be cleaned out. Flow had also damaged the metal gate on the south side of the
road crossing, and the gate will need to be repaired or replaced.
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