Estimation of Magnitude and Frequency of Peak Discharges at Ungaged Sites

ents near these stations become increasingly steep. The generalized skew map selected for this study was based on a grid spacing of 20,000 meters and 12 stations. The part of the map for western Oregon is shown in figure 8. This map was selected because it had the smallest mean square error while having skew isolines that are smooth and with no peaks or valleys. This map offers considerable improvement in mean-square error over either the generalized skew map provided by Bulletin 17B or the average of the skews of the 267 stations. Figure 8 is provided for illustration only. A GIS (ARC/ INFO) grid of the generalized skew coefficients may be obtained from the Oregon Water Resources Department ([email protected]). It is recommended that generalized skew for a watershed be determined from this grid (using a GIS overlay analysis) rather than from a plotted map of generalized skew isolines.