Sediment Yield Results
NTU-based multiple-regression models explain more variability in SSCs
than Q-based models (Table 3), making them our first choice for
predicting annual sediment yields. However, the turbidity sensor failed
at times, and there are no substitutes for NTU measurements, such that
NTU-based models could not be used alone. Q-based models could be
applied with fewer gaps, but data were still lacking for the shoulder
periods of each season. Photographic and field observation evidence of Q
during ungauged shoulder periods led us to use average SSCs at low flows
to fill early- and late-season gaps. Bridging the three methods in
preferential order allowed sediment yields to be estimated (Table 4).
Given that there is minimal sediment transfer at low flow, using our
approximation for shoulder periods makes little difference to the
estimated sediment yields; 5.4% and 13% (2015) and 0.17% and 1.7%
(2016) of the total open-channel season sediment yield in Carnivore and
Chamberlin Creeks, respectively, was approximated from average SSCs at
low flow. Furthermore, our sediment yield results are supported by
estimates based on sediment accumulation rates measured in Lake Peters
(Thurston, 2017).
Total seasonal suspended sediment discharge into Lake Peters from
Carnivore Creek is one or two orders of magnitude higher than suspended
sediment discharge from Chamberlin Creek, with the former contributing
96% of the total yield from these two major tributaries (Table 4). When
normalized by catchment area and averaged across 2015 and 2016, the
specific sediment yields were 58 and 33 Mg km-2yr-1 from Carnivore and Chamberlin Creeks,
respectively. Sediment yield for Carnivore and Chamberlin Creeks is 59%
and 37% greater, respectively, in 2016 than 2015. Most of the suspended
sediment loads in both creeks are transported within a few days during
discrete events (Figure 5). In Carnivore Creek, over 49% and 50% of
the sediment yield is modeled to have been discharged in 48 consecutive
hours for 2015 (August 3-5) and 2016 (July 7-9), respectively. In
Chamberlin Creek, 12% and 57% of the sediment yield is modeled to have
been discharged in 48 consecutive hours for 2015 (August 3-5) and 2016
(July 7-9), respectively.
Discussion