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Resolving Structural Influences on Water-Retention Properties of Alluvial Deposits

^a U.S. Geological Survey, 345 Middlefield Road, MS 421, Menlo Park, CA 94025
^b U.S. Geological Survey, 5735 Kearny Villa Road, San Diego, CA 92123

View larger version (48K): [in a new window]   Fig. 1. Theoretical structural effects on water retention for a fluvial sample and a debris flow sample, both of which are well stratified. A fluvial sample is expected to have a broader pore-size distribution than a debris flow sample of comparable particle-size distribution because of its greater abundance of both small and large pores.

View larger version (40K): [in a new window]   Fig. 2. Sheep Creek Wash and Oro Grande Wash and their associated fan deposits in the western Mojave Desert, San Bernardino County, California (adapted from U.S. Geological Survey, 1:250,000 San Bernardino quadrangle and modified from Weldon, 1985). Core samples were collected from the lower reaches of each wash. Boreholes L and L-1 were drilled directly in the channels, while L-2 and F were drilled into the adjacent fan surfaces.

View larger version (63K): [in a new window]   Fig. 3. Sample classification scheme, based on geometric particle-size standard deviation and stratification, used to distinguish between fluvial and debris flow sediments.

View larger version (22K): [in a new window]   Fig. 4. Laboratory controlled-liquid volume apparatus for measuring wet- to mid-range water retention values on large, undisturbed core samples (Winfield and Nimmo, 2002).

View larger version (25K): [in a new window]   Fig. 5. Cumulative particle-size distributions for core samples collected from (a) Oro Grande Wash and (b) Sheep Creek Wash.

View larger version (22K): [in a new window]   Fig. 6. Water desorption measurements and curves fitted using the Rossi–Nimmo (1994) junction model for core samples from (a) Oro Grande Wash and (b) Sheep Creek Wash.

View larger version (17K): [in a new window]   Fig. 7. Textural variables compared with maximum water content (max) and Rossi–Nimmo (1994) fit parameters (scaling parameter for water potential, o; curve-shape parameter, ). Scatter plots show comparisons with (a, c, e) geometric mean particle diameter (Mg) and (b, d, f) geometric standard deviation (g), for n = 10 samples. Symbols indicate sample categories of Fig. 3, with results for individual samples listed in Table 3. Solid symbols represent fluvial samples and open symbols represent debris flow samples.

View larger version (19K): [in a new window]   Fig. 8. Structural variables compared with maximum water content (max) and Rossi–Nimmo (1994) fit parameters (o and ). Scatter plots show comparisons with (a, d, g) bulk density (b); (b, e, h) trapped air fraction of porosity (Ae); and (c, f, i) porosity-based randomness index (s), for n = 10 samples. Symbols indicate sample categories of Fig. 3, with results for individual samples listed in Table 3. Solid symbols represent fluvial samples and open symbols represent debris flow samples.