Overland erosion due to freezethaw cycling
11
The total sediment mass transported during each test, as reflected in the sedi-
ment samples, is given in Figure 8. The controls show a generally decreasing
trend with increasing moisture content of the soil, while the FT show an in-
creasing and then decreasing trend with soil moisture.
The mean sediment transport rate, derived from the total mass transport, is
also given in Figure 8 for each experiment. The low and intermediate moisture
controls eroded more rapidly than the high moisture controls. The intermediate
moisture FT sediment transport rates were much higher than those of the high
moisture series. The effect of slope can again be clearly seen in both C and FT
results.
The ratio of FT to C for each of the parameters discussed above is given in
Figure 8 for the test series. The ratios of the median, time weighted, and mean
concentrations and the mean transport rate are all tightly grouped and generally
increasing through the low and intermediate soil moisture series. These ratios
separate at high soil moisture, but each shows the same trends. Maximum
concentration ratios oscillate around the grouped ratios through the low and
intermediate series, and show a similar though less extreme trend through the
high soil moisture tests. The relative importance of FT as increasing with soil
moisture is clearly shown in these results.
The results presented thus far were all derived from the sediment transported
from the soil bins by the applied surface runoff. We developed two norms or
measures of cross-sectional change that are reported in Figure 9. L2 is a root
meansquare measure of the change in bed elevation at a section resulting from
the flow event, and Linf is a measure of the maximum bed elevation change at any
point along a cross section.
Our first observation is that both measures are providing very similar infor-
mation concerning cross-sectional change. They indicate small change in the
controls for both the intermediate and high soil moisture series, with all less than
1 cm throughout the high soil moisture series. The measures of both FT cross
sections generally increase through the low and intermediate soil moisture series,
indicating enhanced erosion with increasing slope and applied runoff.
At high soil moisture the slope dependence of cross-sectional change is again
clear, but the dependence on runoff rate is not indicated. The differences between
the measures of the FT and C cross sections in the low soil moisture experiments
are greatly reduced from those at higher moisture.
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