In the case of the tarp treatment, Zhang et al concluded that steady
state soil loss rates for section 1 during each 15 minute interval could
be estimated from
, S10-15 = L0-15 /A1 (4a)
S115-30 =
(L15 -30 -
L0-15 ) / A1 (4b)
S130-45 =
(L30-45 -
L15-30 ) / A1 (4c)
S145-60 = (L45-60 -L30-45 ) / A1 (4c)
where L is the average steady state delivery at the outlet (g
min-1) for the respective time interval, and A1is the projected area of section 1. Eqs 4a-4c provide estimates of soil
loss rates (g m-2 min-1) that are
consistent with the approach that generated the sediment discharges (g
m-1 min-1) presented in Table 1.
However, in analysing the data for the screen experiments, Zhang et al
concluded that the steady state soil loss rates (g m-2min-1) from each section could be estimated from
S10-15 = L0-15 / A1(5a)
S215-30 =
(L15 -30 -
L0-15 ) / A2 (5b)
S330-45 =
(L30-45 -
L15-30 ) / A3 (5c)
S445-60 = (L45-60 -L30-45 ) / A4 (5d)
where S1 , S2 , S3 , and S4 are the soil loss
rates from sections 1, 2, 3, and 4 for the corresponding 15-minute
interval in g min-1 m-2,, andA1 , A2 , A3 , and A4 are the projected areas
of the respective sections. No theoretical or logical reason was given
for Eq. 5. As noted above, the scheme shown in Figure 4 applies to both
the tarp and screen experiments when all sections are exposed to rain,
Logically, when comparable runoff rates from the screen and tarp
experiments occur during the final 15 mins of each rainfall event the
spatial variations in soil loss rates in the screen experiments should
follow that same pattern as seen in the tarp experiments. However, as
shown in Table 2, that does not occur when Eq. 5 is used to estimate the
soil loss rates in the screen experiments. Although it is possible that
flow detachment did occur in some of the Zhang at al experiments, the
conclusion that situation flow detachment occurred in all the screen
experiments and in all the tarp experiments on the 27 % slope and the
tarp experiment with 120 mm h-1 rain on the 18 %
slope was based not only an inability to measure detachment by raindrop
impact but on dubious data soil loss rates in the screen experiments.