--> Abstract: Geostatistical Analysis of Hydrostratigraphic Units in Alluvial Fan Deposits in the Santa Clara Valley, CA, by C. L. Creasey and S. J. Dreiss; #90958 (1995).
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Abstract: Geostatistical Analysis of Hydrostratigraphic Units in Alluvial Fan Deposits in the Santa Clara Valley, CA

Carol L. Creasey, Shirley J. Dreiss

In the Santa Clara Valley, California, alluvial fan deposits are of particular interest because of their widespread distribution, importance as aquifers, and susceptibility to groundwater contamination. We have employed Previous HitbinaryNext Hit indicator geostatistics to describe quantitatively the location and spatial correlation of relatively high and low permeability units of alluvial fan deposits in three different fan environments (proximal, medial, and distal). The geostatistical descriptions generated exhibit significant differences due to their relative positions on the fan deposits. Near the fan head the variograms show anisotropy and the largest range and sill. The horizontal variograms in the distal portion are isotropic and display the smallest range and sill. The variograms fo the medial site show intermediate characteristics.

Kriging of the Previous HitbinaryTop indicators estimates the probability of high permeability in the non-sampled areas and yields a description of the site hydrostratigraphy and associated uncertainty in three dimensions. At the proximal site zones of similar probability appear elongated, indicating buried channels. Kriging results at the distal site show low probability of high permeability with zones tending to be thin and more continuous, suggesting sheetflow deposits. At the medial fan probability zones are more interconnected which may be attributable to a network of shallow channels and sheetlike deposits. In addition, the kriging estimates can provide useful guidance when designing clean-up strategies by indicating regions where there is the highest probability of high permeability zones for flushing out contaminants and the highest probability of potential flow boundaries. Moreover, kriging will aid in assessing where more data is needed by estimating where the greatest uncertainty in the hydrostratigraphy exists.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California