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<br />GEOLOGY <br /> <br />r-- <br />C\1 <br />C\J <br />~ <br /> <br />Landslides <br /> <br />1. Question - Are there landslides in the Sandstone Res~rvoir Basin? <br /> <br />Answer <br /> <br />- There are two large landslide areas, one on Big Sandstone <br />Creek and one on Savery Creek, <br /> <br />The slide area on Big Sandstone Creek would not be in <br />contact with the impounded water at normal water surface <br />or even at the lOa-year flood level. The water would <br />just reach the southwest toe of the slide at maximum <br />water surface.1/ <br /> <br />On Savery Creek, the impounded water would be in contact <br />with the slide for about one-half mile at normal water <br />surface and approximately for the same distance at the <br />laO-year flood level (a flood of this magnitude would <br />raise the level of the reservoir only 1.6 feet above <br />normal). Approximately 1,2 miles of the slide would / <br />be in contact with the water at maximum water surface,l <br /> <br />The landslide area has moved as a series of blocks, not the <br />entire slide area at one time. The area that would be in <br />contact with the water involves a relatively stable toe, <br />presently saturated as evidenced by numerous seeps and ponds, <br />and topography reduced to a low angle, Most recent movement <br />has been in slow-moving blocks far to the east of the reser- <br />voir's area of influence. The probability of renewed move- <br />ment is hypothetical but if movement did occur it probably <br />would be similar to the original mechanism and be on a step- <br />by-step basis and not involve sudden, rapid sliding and, <br />therefore; -would not be a hazard to the reservoir or dam. <br /> <br />2. Question <br /> <br />Are there landslides in the Pot Hook Reservoir basin? <br /> <br />Answer <br /> <br />There are some small slides in the basin, They are <br />steep area saturated by flows from several springs, <br />problems are anticipated from these small slides, <br /> <br />in a <br />No <br /> <br />At the left dam abutment, a small area would overlap some <br />slide material; this material will be removed during <br />excavation for the dam foundation. <br /> <br />1/ Maximum water surface is an extremely rare and temporary situation, <br />It is the result of the maximum probable runoff event that could occur in the <br />drainage area above the reservoir. This event is so remote that a frequency <br />cannot be assigned to it, but the likelihood of it occurring is less than <br />1 in 1,000 years, The water surface would be within 1 foot of the maximum <br />water surface elevation for only about ,11 hours should such an event occur. <br /> <br />- <br />