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<br />I") ... ,-, .~. <br />':'J..j ;) <br /> <br />. <br /> <br />. <br /> <br />4. Seasonality of Annual Streamflow <br /> <br />The seasonal cycle of streamflow plays an important role in water and natural resource <br />management. The month with the peak flow corresponds to the "flood" month and may correspond to the <br />month when the largest sediment yields are generated. A tendency for the peak flow to occur earlier/later <br />in the year can reflect a change in the manner in which the resource is managed. The variation in the <br />average month of peak flow is assessed using a moving window analysis using lowess with window <br />widths of 20 and 44 years. The Archuleta gage shows (figure 4a) a tendency for the peak flow to come <br />later in the year in the second half of the record. .liowever, the most recent trend is towards an earlier <br />peak, The twO nearly 20 year "wet" periods (pre-1948 and 1974-93) are different in terms of this criteria <br />with a tendency for the peak flow to come later in the year in the latter. <br />The trends for the timing of the peak annual flow at the Bluff gage are similar (figure 4b). It is <br />interesting to note that in 1977 (the driest year on record), the Archuleta gage recorded the peak annual <br />flow in month 8, rather than month 5 or 6, which is the usual time of year, Delayed pellk flows also <br />occurred at the Bluff gage in 1970, 72 and 77. The indicated sWfts in seasonality are not large enough to <br />be of concern for reservoir management. Likewise at these sites the incidence of extreme flows in the <br />seasons other than spring/early summer is low enough that no significant differences over the record are <br />established, <br /> <br />May 25, 1997 <br /> <br />5 i <br />