Silver Creek - Division of Water Quality - Utah.gov

Silver Creek Watershed TMDL Final Report
Seasonality and Statistical Analysis of Uncertainty
Variability and Uncertainty
As discussed in the body of this report, the issue of statistical reliability of data analysis was
addressed by clustering the individual data points in Bi-Monthly (seasonal) time periods. This
allowed for analysis of seasonal patterns. On the average there are 5.5 data points per period for
Cadmium and 5.6 data points per period for Zinc. These numbers provide reasonable statistical
validity for the conclusions presented. Table 1 shows average statistical parameters for the two
constituents.
Table 1: Average Statistical Parameters
Constituent
Coefficient of Coeff. of Variation of the
Variation
Means
Cadmium 118% 50%
Zinc 82% 35%
The coefficients of variation above indicate that typical data points for cadmium and zinc are, on
average, within 118% and 82%, respectively, of the mean value. However, there exists
significant uncertainty as to the accuracy of the estimated means for these clusters. The
coefficient of variation of the means represent how tightly clustered the mean values are
(between stations) relative to the mean value.
Seasonality
The annual pattern of normalized zinc concentrations is shown in Figure 1. As indicated by the
graphical representation of the normalized data, this annual pattern is consistent throughout the
reaches of Silver Creek between Wanship and Park City. Concentrations increase sharply
between the September-October period and the November-December period, even though flows
do not yet show significant upswing. So it is not necessarily a feature of flow-induced scouring.
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