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Biological Opinions - Bureau of Reclamation

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Figure 11.13. Williamson River observed, proposed action and Observed IGD discharge for water year 1994.<br />

Proposed action IGD daily discharge was calculated for water years 1981-2011 based on a 7-day moving<br />

average.<br />

NMFS also evaluated the effect <strong>of</strong> the proposed action on flow variability by calculating and<br />

comparing the monthly coefficient <strong>of</strong> variation <strong>of</strong> IGD daily flows between the observed<br />

hydrograph and the proposed action hydrograph. The coefficient <strong>of</strong> variation is a common<br />

measure to quantify variability <strong>of</strong> a distribution and is particularly useful for comparison <strong>of</strong> data<br />

sets with different means, yet is only useful when applied to individual years. As an illustration,<br />

NMFS presents the coefficient <strong>of</strong> variation <strong>of</strong> IGD daily flows by month, for water year 2011<br />

(Figure 11.14). The coefficient <strong>of</strong> variation for the proposed action IGD flows is greater than<br />

observed in 8 <strong>of</strong> the 12 months (Figure 11.14).<br />

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