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