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Challenges in reliably estimating peak flows for water resource management and planning are many, however, one impediment is the estimation of flood skew. In the US, the three-parameter Log-Pearson Type III (LP3) distribution is recommended to relate the probability of exceedance to a specified design flood discharge, e.g. the 100-year flood. Estimation of all three parameters requires flood skew which is typically biased and subject to large sampling errors because of short streamflow records. Thus, use of a regional flood skew is recommended to reduce bias and improve estimates of selected return period discharge. The most common source from which regional flood skew is obtained comes from the Hardison map published in 1979. However, efforts to update regional skew values have been ongoing, whereby regional regression analysis is used with geomorphic data from several sites to develop a more informed regional skew. Because recent studies have shown flood skew is significantly affected by surface and groundwater interactions, updates to regional skew values should consider this process where appropriate. The Suwannee River Basin in northern Florida is one such watershed where extreme surface and groundwater interaction occurs and regional flood skew values have not been updated since publication of the Hardison map in 1979. Therefore, we developed a new regional skew for the Suwannee River Basin using Bayesian regression analysis that accounts for surface and groundwater interactions. A regional skew value of -0.349 is proposed as a new value for regional flood skew the Suwannee River Basin, which reduces RMSE, particularly at higher return period flows, compared with the commonly used map value of regional skew, -0.100. |
