_INSPECTION - C1982057 (73) - Laserfiche WebLink

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A G' July 28, 2010 C-1982-057/Seneca II-W Mine DTM necessary. Similar erosion was observed in the channel segment just downstream of Stock Pond T-27. These sites and similar locations will need to be carefully checked and repaired during the 2010 field season. Hillslope gullies will need to be repaired in accordance with the approved Rill and Gully plan. Areas that have been subject to recurrent erosion due to concentrated flow will need to be repaired as stabilized tributary channels, incorporated into the permanent drainage network. During the inspection on 7/29,drainages in the northern portion of the 016 watershed were walked, including segments of Channel PM-3,PM-3A,PM-6, and adjacent slopes. The following observations pertinent to site grading and channel and hillslope erosion were made: • Two surge structures were constructed in series along the upper third of PM-3. These structures appear to be functional and in good condition. There are gullies on the inlet slopes of the lower surge structure, associated with both the main permanent channel inlet and a tributary drainage that enters the structure from the east. Stabilization of both gullies is warranted; use of riprap or TRM liner would appear to be necessary for the main channel inlet, and check structures or TRM along the tributary inlet. • Minor settling cracks and rills along the reclaimed slope west of the upper segment of PM-3 appear to be filling in and healing over with vegetation. • Five hillslope gullies ranging from approximately 8"to 14"deep have eroded along a portion of the west facing slope of the upper PM-3 drainage. These gullies were observed by walking the N/S fenceline that that runs along the slope,north of the gate on the maintenance access route. These gullies appear to be marked on the 2010 R&G map, and will need to be stabilized. • Several additional gullies of similar depth were observed to the south of the maintenance gate,between the vicinity of the fenced"aspen farm"and the fenced shrub plot to the west. One of these gullies approximately 16"deep crosses into the fenced shrub plot approximately 150' south of the northeast corner of the plot. Stabilization of the gullies is warranted. • Permanent Channel PM-3A is a TRM lined channel from its junction with PM-3 up to the lower boundary of the fenced shrub plot. Within the fenced shrub plot,the upper end of the channel was originally a gully,which was graded to a V shaped channel and seeded. The channel has subsequently incised 12"to 16"deep. Stabilization is necessary; grading and TRM installation would appear to be warranted. Along the lower segment of the channel below the fenced plot,TRM liner has been ripped and undercut in several locations, and maintenance is warranted(noted on R&G Map). • Near the upper end of the Channel PM-3, a gullied tributary extends down to the channel from a former equipment access route, and stabilization(installation of closely spaced checks or grading and TRM installation) is warranted. The small ridgeline watershed to the north of the PM-3 drainage was also inspected on 7/29. This watershed includes Channels PM-4,4A, 4B,4C, and 4D. 4,4A,and 4B are stable riprapped channels. 4C is a stable grass- lined channel that directs flow away from the repaired ridgeline landslide location. Channel 4D is a very steep TRM lined channel that runs down the slope on the east side of the ridgeline,through the area impacted several years ago by the ridgeline landslide. A temporary plastic pipe is staked in place along the length of Channel 4D, to convey flow from Culvert PM-11 at the upper end of the channel,down to the toe of the channel. Along most Number of Partial Inspection this Fiscal Year: 0 Number of Complete Inspections this Fiscal Year: 1 Page 4 of 19