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<br />Wells, W.G., II., 1981, Some effi~cts of brushfues on erosion proo:esses in coastal
<br />Southern California, in Erosion and Sediment Transport in Pacifk Rim
<br />Steeplands: Christchurch, New Zealand, International i.ssociation of
<br />Hydrological Science, no. 132" , p. 305-342.
<br />This paper reports on some of tIe effects of ftre on erosion proces,es in chaparral settings.
<br />In the: discussion on water repellency, the author describes the irnpications of an intensely
<br />repellent subsurface layer on so~ movement. He emphasizes that the presence of such a
<br />conftning layer effectively reduces the storage capacity of the soil mande by 20 times or
<br />more, limiting hydrologic activity to the upper 5 cm. Photographs depict the wettable bed
<br />and surface soils of a levee-borde::ed rill, overlying a nonwettable so~. The autb.or points out
<br />that: in areas with water-repellent ,;oils" these miniature debris flo'v types of rills tend to
<br />predominate over other rill formations. He suggests that the riUs form as a result of
<br />increased pore pressure above the water-repellent layer, which reduces the intergranular
<br />stress and shear strength 0:: the soil mass, and ultimately leads to failure in the form of a
<br />small debris flow. Evidence frorr several storm events is provided, but the author notes that
<br />further testing is needed to confirm the process.
<br />
<br />Wessel, A. T., 1988, On using the effe,ctive contact angle and thl water drop
<br />penetration time for cla,;si.fication of water repellency in dune soils: Earth
<br />Surface Processes and Landforms, v.13, no. 6, p. 555-56:.
<br />This paper compares and contra';ts various methods used to classifT water repellency. The
<br />methods used in this study involved measuring the water drop penetration time (\XIDPT)
<br />and the effective or observed solid..liqmd contact angle, a.', rather than the contact angle a..
<br />The investigation determined th:,t water repellency in dune soils w lS best characterized by
<br />water drop penetration time, because it subdivided water-repellen t soils and was easy to
<br />measure. It was also found to be a better indicator of the erosion pc tential of soils, since the
<br />time required for inflltratioc of precipit:,tion is related to the amount of surface runoff.
<br />
<br />Witter, J.V., Jungerius, P .D., and ten Harkel, M.}., 1991, Modeli ng water erosion and
<br />the impact of water repl~llency:" Catena, v. 18, p. 115-124.
<br />Measurements of surface runoff and sediment yield from coastal dune plots in the
<br />Netherlands were used to develop a regression model for water er,)sion. Water repellency
<br />was expressed differently in the two catchments studied, and subsequently r,esulted in very
<br />different responses to precipitation. The more water-repellent catchment yielded runoff that
<br />was an order of magnitude higher than the wettable catchment. However, sediment yield
<br />was an order of magnitude less. 1be authors attributed this anomaly to presence of moss
<br />vegetation in the less wettable catchment. Although moss inducec water repellency in the
<br />dune sands, it also acted to srabiLze the soil surface, and thus count, red the effects of higher
<br />runoff. Since soil moisture con,lit ons were found to signifIcantly Lnfluence the expression
<br />of water repellency (and hence, nrnoff parameters), the author slggested that antecedent
<br />moisture should be taken into account when modeling water erosior in dune ,:n0.ronments.
<br />Note: This study observed higher pH values in the more water-rep',llent soils, in contrast to
<br />Roberts and Carbon (1971), who detetmined that an acidic pH w: s associated with severe
<br />repellency.
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