RELATIONSHIP OF DISPLACEMENT RATE TO GROUND WATER TABLE HEIGHT IN THE SHERWOOD HILLS SLUMP, PROVO, UTAH

The Sherwood Hills slump is an active landslide on the East bench of Provo, Utah, in the foothills of the Wasatch Mountains. The slump, approximately 400 meters by 150 meters in size, has been active since at least 1998 and has caused significant property damage to residences in the neighborhood in which it is located. Utah Valley University students and faculty have been measuring slide displacement one to six times per year since 2004 using RTK GPS. The slump has moved 41 cm since monitoring began. Minimum displacement rates have been calculated for periods between surveys by dividing the amount of movement between surveys by the duration of time betweens surveys. The slump has moved at a fairly consistent background rate of approximately 1 to 3 cm/yr punctuated by three periods of rapid movement. In 2010, 6.3 cm of movement was recorded by surveys made 6 months apart, giving a minimum velocity of 12.6 cm/yr. In 2006, the slide moved 9.3 cm in 3.9 months, a minimum velocity of 28.7 cm/yr. In 2005 the slump moved 15.6 cm in 12.8 months, a minimum velocity of 14.7 cm/yr. If the movement in 2005 actually occurred in 3 months, the slump’s velocity was 54 cm/yr. Rapid movement in 2006 and 2010 occurred between February and September. We have compared the slump’s displacement to precipitation records and water table height measurements made in wells in the slump block since 2001 by the Utah Geological Survey. Time series plots of slump displacement and water table height qualitatively reveal that peaks in water table height correspond with the three periods of rapid slump movement. Calculated minimum displacement rate and the log of the minimum displacement rate were plotted against water table height to quantitatively ascertain their relationships. Log minimum displacement rate has a strong linear correlation with water table height (R² = 0.82), whereas minimum displacement rate is less well correlated with water table height (R² = 0.54). Precipitation also correlates with slump movement. The strong correlation between log of displacement rate and water table height raises the possibility that at high water table levels relatively small additional increases in the water table could produce large increases in slump velocity.