L-Moments and 100-Year Flood Peaks at Twelve Long-Record USGS Gauges: Exact PWM Identifiers, GEV Versus Gumbel, and a Regional L-CV of 0.34

Hosking and Wallis L-moments are linear combinations of probability-weighted moments and yield closed-form GEV parameter maps. I compute them for annual peak discharges at twelve USGS gauges with long records (Potomac, Wabash, French Broad, Suwannee, Guadalupe, Missouri, Colorado, Sacramento, Willamette, Kansas and two Potomac tributaries). Median L-CV is 0.302 and median L-skew is 0.333; ten of twelve sites have negative GEV shape (heavy upper tail). The mean absolute gap between GEV and Gumbel 100-year peaks is 31%. Sacramento at Verona is a discordant light-tailed outlier (L-skew -0.117, z-score -2.50). Regional mean L-CV is 0.342. The identity that the first L-moment equals the sample mean holds at every site.