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} Coal- Basin Tract <br /> August 18, 1996 <br /> erosion from normal A <br /> thunderstorm activity is <br /> much greater, and prob- <br /> able. The combination <br /> of the bend in the <br /> stream below the scarpa•• •�• <br /> W�� Croce—•eotl.n <br /> face and the normal hel- <br /> ical flow pattern pro- r��� A ....«. Well � <br /> r.�� <br /> ! video a constant oppor- <br /> tunity for undercutting <br /> 1 the stream bank. o u to r«t <br /> if the scarp face starts root <br /> to erode away, the creek N� <br /> will be loaded with Plan vier TWIN PORTALS <br /> fine-sediment and larger <br /> fractions up to 8 inches MM <br /> in dianeter. If the <br /> scarp face is eroded in FIGURE 4 Plan and cross-section views of <br /> conjuction with a debris the proposed remedial action at the twin <br /> flow, the rook mass will portals. <br /> probably be cemented to- <br /> gather creating a large <br /> diversion or blockage forcing the stream to possibly flow across <br /> the processing area. This diversion may completely bypass the <br /> flume area. <br /> There are two possible ways to control the possible collapse of the <br /> scarp face. one is to build several layers of gabions which could <br /> control the cutting effect of Dutch Creek. This action would pro- <br /> vide a neutralizing effect to the normal flow of a stream shown in <br /> Figure 3 . A second option is terracing the scarp face shown in <br /> Figure 2. This involves the removal of some of the spoils area and <br /> upwards of 20 feet including the overhanging portion of the scarp <br /> face. This material could be placed into a sediment pond which <br /> overlooks Coal Creek on the northeast corner of the spoils pile. <br /> This action would 1) reduce the volume of material above the creek, <br /> 2) lay back the scarp face reducing potential for slope failure, <br /> and 3) fill in the pond, a source of potential failure. <br /> 2)- The method of providing continual drainage at the twin portals <br /> appears to be sound. The availability of material in sufficient <br /> volume and size capable of clogging the 48 inch opening appears to <br /> be remote, at best. <br /> 3)- The concern about potential slides along the road network will <br /> be addressed at a later date when time permits. Available geologic <br /> 6 <br />