Laserfiche WebLink
Bruce Park Landslide Project No. 25-196 <br />Bowie Mine #2 <br />will not create a magnitude great enough to affect the existing landslide. We also believe the <br />slight reduction in stability would not cause a catastrophic (rapid moving) slope failure. <br />DEBRIS FLOW POTENTIAL <br />The Division of Water Resources is concerned that a catastrophic slope failure due to <br />seismic events associated with underground coal mining activities would cause a large enough <br />wave to overtop the dam. As previously discussed, we do not believe the anticipated seismic <br />events are significant enough the cause a catastrophic slope failure. However, if a catastrophic <br />failure were to occur and was large enough to compromise the integrity of the dam, we believe <br />the following: <br />• The landslide mass would likely have to liquefy and move as a debris flow, <br />• The volume of materials from the landslide must displace a sufficient amount of water to <br />overtop the dam, and/or <br />• The wave action caused by the slope failure would have to be in excess of 10 feet high <br />0 to reach the dam crest. <br />The following discussions address the concerns presented above: <br />The landslide materials consist of low to high plasticity clay. Materials with high fine <br />contents (passing No. 200 sieve), especially clay fines, are at low risk for liquefaction. Based on <br />test results, the fine contents in the landslide materials are in excess of 70 percent indicating <br />low susceptibility to liquefaction. Therefore, we believe there is low risk of the landslide moving <br />as a debris flow due to liquefaction. <br />If the landslide mass were to completely displace into the reservoir, the resulting change <br />in water lever would be about 2 to 3 feet. We estimated the landslide volume (volume of solids <br />and volume of water) to be about 1.5 to 2.0 million cubic feet. If that volume is spread over a <br />reservoir with a surface area estimated at 1.3 million square feet, it results in a water level rise <br />of about 1 to 2 feet. With a free board on the dam in excess of 10 feet, we do not believe that is <br />sufficient enough rise to overtop the dam. <br />0 We also analyzed water wave amplitudes across the reservoir that could be produced if <br />the landslide were to accelerate in the reservoir. If the landslide were to accelerate during a <br />7