FT concentrations were similar, while corresponding mid-moisture FT concentrations were consistently
higher. In contrast, maximum FT concentrations followed soil moisture from high to mid to low. Low
and mid soil moisture C concentrations were comparable, while high moisture C concentrations were
generally lower. The high moisture series had saturated soil conditions through most of the soil depth,
and the highest bulk density. Trends in concentration of eroded soils with soil moisture are not clearly
indicated by these results, though erosion resistance increased in the high moisture C series. Our initial
interpretation is that the decrease in C erodibility at high soil moisture resulted from greater soil
consolidation and/or enhanced cohesiveness.
Time-weighted average sediment loads (g/min) from the FT and C bins during each test and the
corresponding FT/C sediment load ratio are presented in Figure 10 with flow condition by slope and soil
moisture series. The FT/C ratio reflects significantly higher sediment loads in the FT bins than in the C
bins, and a generally increasing effect of FT with soil moisture. Sediment load ratios were in the range
from 2 to 4 for the low and mid soil moisture series, and up to 12.7 in the high moisture series. The
effects of both flow and slope on FT and C sediment loads are large and apparent in this figure. The high
soil moisture FT and C series exhibited generally reduced sediment loads relative to lower soil moisture
tests. FT sediment loads of Figure 10 are inversely related to the test durations given in Figure 4. FT/C
ratios of mean, median, time-weighted average, and maximum concentrations, and sediment load with
flow condition are compared in Figure 11 by slope and soil moisture series. The single valued median
and maximum concentration ratios are frequently outliers, while the other measures are comparable.
There is a systematic increase in the ratios with soil moisture, clearly indicating an increased importance
of FT. The large difference in slope does not produce a trend in FT/C, and trends with applied flow are
not consistent between the soil moisture series. Total FT and C sediment sample mass transported during
an experiment was obtained by multiplying the average sediment load by test duration. These results and
the corresponding FT/C transport ratios are given in Figure 12 with flow condition, by slope and soil
moisture series. The C results show generally decreasing total transport with increasing moisture content
of the soil, while the FT results do not show a clear trend in total transport with soil moisture. Erosion of
the FT bin was used to determine test duration, providing a tendency to equalize the total FT transport of
the different soil moisture series. Like sediment load, the total transport generally increased with both
flow and slope, while FT/C ratios were not sensitive to these parameters.
The sediment load data of the individual experiments were grouped by soil moisture, slope, and
flow to better define trends and relationships, and these results are presented in Table 6. Average
sediment load for the complete set of experiments was 37.7 g/min FT and 12.5 g/min C, with a ratio of
3.03. When grouped by soil moisture series, the averaged C load diminished sharply for the high
moisture (saturated) soil. The averaged FT sediment load increased from low to mid moisture, and also
decreased significantly at high moisture. FT/C ratios 2.41, 3.04, and 4.96 clearly indicate an increasing
effect of FT with soil moisture content. A second grouping of the experiments by slope indicates that
average FT and C sediment loads were directly proportional to slope. However, the equal FT/C ratios
indicate that the effect of FT on sediment load was unrelated to slope. With the experiments grouped
according to flow, we observed average FT and C sediment loads that are proportional to flow. Again,
the nearly equal FT/C ratios show that the effect of FT on sediment yield was unrelated to flow. The
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