Laserfiche WebLink
Coal Basin Tract <br /> August 18, 1996 <br /> CROSS SECTION A - A' <br /> A' <br /> NNW SSE <br /> Spoils Pile 8300 <br /> A Scarp 8200 <br /> Face <br /> tat terrace G 200 <br /> Floodplain I + <br /> Feet ELEV <br /> Dutch Cr <br /> FIGURE 2 A cross-section (A-A' ) view across Dutch Creek, the <br /> scarp face, and the spoils pile. <br /> creek is about 22 feet wide at the turning point and is choked with <br /> large cobbles from numerous debris flows over past years, particu- <br /> larly the one in 1977. Overall, the sizes range from sand-size to <br /> greater than 48 inches in diameter. The percentage of solids lar- <br /> ger than sand-size appears to be greater than 50 percent. <br /> The fraction greater than sand-size in the creek bed is well-com- <br /> pacted, almost cemented by the clay fraction. The bank on the <br /> south side of Dutch Creek is composed of alternating layers com- <br /> posed of clay lenses, sand, gravel, and cobble zones. This uncon- <br /> solidated unit appears to be easily erodible as evidenced by the <br /> mounds of sand and gravel along the south edge of the creek. <br /> In order to control the water flow in the creek, the cobbles have <br /> been mounded on both sides to provide a defined channel. The south <br /> creek bank and scarp face can be undercut by a debris flow or <br /> normal stream flow at any time. The steepness of the scarp face <br /> makes it very susceptible to erosion while the spoils pile appears <br /> to be closer to the angle of repose. The scarp face is bare of <br /> vegetation and has been subject to rilling. The normal helical <br /> flow and cutting power of the stream is shown in Figure 3. <br /> A small stream to the north which flows into Coal Creek clearly <br /> shows the force and destruction of debris flows. The stream <br /> 4 <br />