1993-11-15_PERMIT FILE - C1981017

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Memo to Steve Renner Coal Basin Examination page 2 partially destroyed by a debris flow in 1977. In 1983 the foundation area of the rock tunnel waste pile was inundated by a 15 foot thick debris deposit. These debris flows travel down the modern stream channels until they reach a lower gradient and cease movement. The coarse rock debris clogs the stream channel causing a topographic inversion. The debris clogged stream channel resembles a debris levee. The stream then relocates on the floodplain. It appears that the coal mine relocated Dutch Creek during the past 90 years to use the floodplain for a shop and storage area. Useable level ground is at a premium within Coal Basin. Dutch Creek was pushed up against the toe of the slope below the old coal refuse pile. The Creek was relocated on top of an older debris flow levee, as evidenced by the mounded, tree - covered land form strewn with coarse debris up to 30 inches in diameter. Apparently approximately a decade ago, Dutch Creek slipped off the debris deposit preferentially eroding into the toe of the softer shale founding the valley slope. This erosion eventually penetrated the well developed bio -mat evident on the slope. Once the bio -mat armor had been penetrated the incision rapidly accelerated. With no specific benchmarks other than my recollection of the location, I would guess that the slope is receding at approximately a foot a year. Obviously this recession must be stopped before it threatens the toe of the refuse pile. In my opinion the most effective way to expeditiously prevent further incision is to relocate the creek away from the toe of the eroding slope. I assume the operator will need to obtain a 404 permit to relocate the channel. The only plausible way to relocate the channel is to doze the coarse debris flow which now forms the north levee of the channel up against the toe of the slope. This will form a buttress against the eroding slope. The length of the affected debris levee is approximately 200 feet. The relocated channel reach should have a constant gradient and should smoothly transition to the gradients immediately above and below, in order to avoid creating an hydraulic knick point. In order to achieve a constant channel gradient, up to fifteen feet of debris may need to be dozed near the middle of the reach. In order to leave a sufficient levee width on the north bank of the straightened channel, it may not be possible to completely straighten the channel reach, rather a gentle bend to the north may result. Care should be taken to avoid sharp angular deflections, because they could encourage lateral incision. During the work significant sediment will be generated. However, in my opinion, the construction of ponds to attempt to control sediment, if possible, would significantly prolong the sediment generating construction. I believe an expeditious effort, conducted near annual low flow in late August or September, should accomplish the task with a minimum