Laserfiche WebLink
<br />The flood magnitudes at these recurrence intervals can be calculated <br /> <br />using only that part of the drainage area below 8,000 feet (2,438 meters). <br /> <br />Using the drainage area below 8,000 feet (2,438 meters) does not imply that <br /> <br />it does not rain above this elevation, but rather that rainfall runoff <br /> <br />above this elevation does not contribute significantly to flood runoff. To <br /> <br />determine the flood characteristics above this elevation requires an <br /> <br />evaluation of snowmelt runoff using methods described by Kircher et al. <br /> <br />(1985). For those sites near the 8,OOO-foot (2,438-meter) elevation level, <br /> <br />flood characteristics may be computed by both methods, and the larger <br /> <br />values used. <br /> <br />The next step in determining flood characteristics at a site depends <br /> <br />on whether the site is ungaged, gaged, or near a gaged site. If the site <br /> <br />is ungaged, then use the values from the regression equations. If the site <br /> <br />is gaged, then the regression results need to be weighted using the site <br /> <br />flood-frequency estimates. The weighting should decrease the time-sampling <br /> <br />error that may occur in a site flood-frequency estimate and should improve <br /> <br />the flood-frequency estimates. This time-sampling error decreases as the <br /> <br />length of record for a site increases. The weighting procedure is des- <br /> <br />cribed by Sauer (1974). The procedure weights the site flood-frequency <br /> <br />estimate and the regression flood-frequency estimate by the years of record <br /> <br />at the site and the equivalent years of record of the regression estimate <br /> <br />using the following equation: <br /> <br />QRt(w) <br /> <br />= <br /> <br />QRt(s) x (N) + QRt(r) x (E) <br />N + E <br /> <br />(8) <br /> <br />.y..r <br />