design there is very little variation within these series. For the water surface slope results flow conditions
13, 46, and 79 represent increasing flow (low → mid → high) in each soil moisture series. The water
surface slopes in the C bins did not change greatly from the initial slopes of 0.176 (8) and 0.290 (15) in
any test. However, significant slope reductions occurred during several experiments in FT bins,
especially in the low moisture series. Post-test soil moisture increased from pre-test levels in the low- and
mid-moisture series of experiments, but not in the high-moisture series (Table 1). Post-test soil moisture
in the FT bin was generally higher than in the C bin, and increased most significantly from pre-test
conditions for the low soil moisture series. These observed soil moisture changes are consistent with the
infiltration measurements of the soil characterization.
The calculated time-weighted flow from each bin is related to the "flow condition" designation of
Figure 4 in Figure 5 by soil moisture series. This figure provides the precise flows associated with each
flow condition. The C and FT flows were essentially equal, with the exception of three mid-moisture
experiments where the C bin experienced slightly higher flows. These flow differences are conservative
as they favor increased erosion in the C bin relative to the FT. Groundwater depths were all zero in the
unsaturated low- and mid-moisture series. Mean groundwater depth measured in FT and C wells before
and after each experiment of the saturated high soil moisture series are given in Table 5. These
groundwater depths are comparable, with before and FT-bin depths slightly greater than after and C-bin
depths, respectively. The pre- and post-experiment data indicate only minor net exchange of water
between the surface flow and groundwater in this series. Comparisons between FT and C groundwater
depths indicate a negligible difference in surfacesubsurface flow exchange between the bins. Minimal
surfacesubsurface water exchange is consistent with negligible infiltration at high soil moisture in the
characterization study.
Integrated Measures of Erosion
The results presented in this section were derived from sediment discharge data for each soil bin
and include several concentration measures, load, and total mass. The strength of these global measures
is that they integrate the processes occurring in each bin, and are not specific to a particular location.
Figures 6, 7, 8, and 9 present mean, time weighted, median, and maximum FT and C outflow sediment
concentrations, respectively, with previously defined flow condition, for each slope and soil moisture
series. Corresponding dimensionless FT/C ratios of these concentration parameters are also given in each
figure. Though parameter values are slightly different, the overall patterns are very similar. Flume
experiments of Lei et al. (1998) indicated that sediment concentrations increased with bed slope, but did
not generally increase with flow rate. In our experiments there is a strong and consistent dependence in
both FT and C concentrations on the bed slope. When other experimental conditions are the same, greater
slope produces greater sediment concentrations from both bins. Like Lei et al. (1998) the eroded FT and
C concentrations have no clear relationship to flow. The FT/C ratios of these concentrations are all
significantly greater than 1, indicating a primary effect of the FT cycle on rill sediment erosion.
Several high soil moisture experiments had C bin concentrations that were low relative to other
tests, and corresponding FT/C ratios were large, indicating that FT effects on soil erosion processes are
generally maximized at high soil moisture. Low and high soil moisture mean, time weighted, and median
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