Prediction of Peak Flows for Culvert Design on Small Watersheds in Oregon

摘要

Forest engineers must estimate flood frequencies for very small watersheds when designing culvert installations. Empirical formulae and simplified rainfall runoff models require considerable judgement to give reasonable results. As an alternative, this study presents equations to predict peak flows on small watersheds in Oregon. Equations were developed from 80 watersheds ranging in size from 0.21 to 10.60 square miles. Six physiographic regions were used, based on previous flood frequency studies. In each region, annual peak flows from gaging stations with 20 or more years of record were analyzed using four flood frequency distributions (Gumbel, two-parameter log-normal, three-parameter log-normal, log Pearson type III). These equations provide a better basis for culvert design on small forested watersheds than rule of thumb or empirical methods.