Perched Water Tables on Hillsides in Western Oregon: I. Some Factors Affecting Their Development and Longevity1
- D. P. Hammermeister,
- G. F. Kling and
- J. A. Vomocil2
Perched water tables on hillsides located on the western border of the Willamette Valley in Oregon in some cases have the potential to transport pollutants from either domestic or agricultural sources downslope to streams, ponds, or reservoirs, resulting in the deterioration of the quality of these waters. In this paper, some factors responsible for the development and longevity of these potentially problem-causing perched water tables on three hillsides were examined. Analyses of hydraulic conductivity data and the relationships between rainfall, soil water pressure potential, and time suggest that permeable rock below 110 cm rather than clayey B horizons is mainly responsible for the development of perched water tables on upper convex slope positions on two of these hillsides. The data also suggest that subsurface flow from the upper convex regions contributed significant amounts of water to the lower convex slope positions. Further, perched water tables developed more rapidly, to a greater extent, and lasted longer in upper horizons of a lower concave region of slope where a shallow perched water table was already present at the onset of rainfall. Finally, perched water tables did not develop in the upper horizons on a third hillside that had no impermeable regions in the soil or upper rock mantle.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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