Stream incision rates were obtained from 16 studies of terraces or stream-associated cave levels in the eastern United States. A log-log regression of age against height above modern river level (ARL) shows that age increases approximately as the square of height ARL. This relation may indicate an increasing rate of stream incision through time. Alternatively, the relation may simply reflect an inherent effect of measured time interval on process rate, as described by Gardner et al., who found that data from hundreds of studies showed a tendency for geologic process rates to decrease for increasing measurement intervals. A regression equation for landscape denudation rates showed that the thickness removed increased as the 0.82 power of the time interval over which the denudation was measured. Gardner et al. suggested that this bias could be removed by the use of statistically derived scaling functions. However, a similar regression equation for the data in this study shows a slope of 0.38, representing a much more rapid decrease in rate with increasing measurement interval than found by Gardner et al. Even after applying the scaling function calculated by Gardner et al., my data show a 19 fold decrease in incision rate for a 103 increase in the measured time interval. This result suggests that the observed decrease in stream incision rates with greater time spans may be at least partly real.

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