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<br />Burcar, S., Miller, W.W. Tyler, S.W, and Johnson, D.W., 1994, Seasonal preferential
<br />flow in two Sierra Nevada soils under forested and meadow cover: Soil
<br />Science Society of America Joumal, v. 58, p. 1555-1561.
<br />This study illustrated the effects of water repellency on infIltration under various soil,
<br />temporal, and plot cover conditions. Researchers evaluated infIltration, runoff and
<br />preferential flow in a sandy soil derived from granitic parent material (Marla), and a finer-
<br />grained, loamy soil derived from weathered andesitic lavas (Umpa). Measurements were
<br />made in the spring and fall (corresponding to high and low antecedent moisture conditions,
<br />respectively), and under forest (accumulations of pine litter) and meadow (little surface
<br />organic debris) vegetative covers. Results indicated that vegetation in the Sierra Nevadas is
<br />extremely important in determining the spatial distribution of water repellency, in that
<br />forested plots tended to have greater water repellency than meadow areas. They also found
<br />that repellency in the Sierras is seasonal and has a major impact on infIltration properties.
<br />Contrary to other literature which suggests that coarser textured soils tend to be more water
<br />repellent, this study found water repellency to be more persistent in the finer-textured
<br />volcanic soil. In the fall, the coarser-textured soil exhibited higher infIltration rates, as
<br />expected, but in the spring, the forested Umpa soil actually had higher infIltration rates,
<br />despite its finer texture. This behavior was explained by the fact that, in the spring, the
<br />persistent water repellent nature of the Umpa enabled deep, well established preferential
<br />flow paths to form, whereas high antecedent moisture conditions in the course-textured
<br />Marla soil caused preferential flow paths to dissipate, thus forcing slower matrix flow to be
<br />the dominant infIltration process. In the fall, however, low antecedent moisture conditions
<br />resulted in less conductive flow paths in the Umpa, and thus, signifIcantly lower infIltration
<br />rates.
<br />
<br />Burch, G.J., Moore, I.D, and Bums, J., 1989, Soil hydrophobic effects on infiltration
<br />and catchment runoff: Hydrological Processes, v. 3, p. 211-222.
<br />Results of this investigation illustrate the diffIculty of predicting how water-repellent
<br />conditions will affect a watershed. Eucalypt forest catchments at two sites in southeastern
<br />Australia showed strikingly different responses to precipitation events, following the
<br />development of drought-induced, water-repellent soils. At the first site, water repellency
<br />(when present) signifIcantly interfered with infIltration, as was evidenced by a comparison of
<br />runoff generation in a forest and grassland catchment. At this site, the grassland catchment
<br />consistently produced more runoff than the forested catchment when soils were wetrable.
<br />However, the scenario was reversed during an isolated, summer storm, when the forested
<br />catchment (which had developed water- repellent soils) generated significantly higher runoff
<br />than the grassland catchment. In contrast, a second forested site, also exhibiting drought-
<br />induced water repellency, generated minimal runoff in response to precipitation events. This
<br />discrepancy was attributed to the dense network of macropores present at the second site,
<br />which enabled the water repellent soils to maintain high infIltration rates via preferential
<br />flow.
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