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Bankfull geometry, Flow-frequency relationship, Dimensionless rating curve, Bankfull discharge, Ungaged watersheds


Dimensionless rating curves to estimate flows and stages of different return periods are investigated in this study for streams located in the Red River Basin of Minnesota and North Dakota, USA. Bankfull flow and depth are used as the reference variables. Ratios of peak flow to bankfull flow and peak flow depth to bankfull depth are developed at twenty-two United States Geological Survey (USGS) stream flow gaging sites for preparing a regional dimensionless rating curve. Individual station curves, regional curves, and frequency plots of dimensionless ratios of flows and stages are developed and presented. The median ratio of the 50-year peak flow to the bankfull flow was found to be 10.7 and the median ratio of 2.4 was found for the 50-year peak flow depth to the maximum bankfull depth. Application of the method is illustrated by applying it to four other gaging station sites in the basin. Flow estimates are compared with the flow frequency data for each example gaging station and also compared to flow estimates generated using the USGS regional regression equations, and the basin characteristics regressions and the bankfull hydraulic geometry regressions developed by the authors. Stage estimates at the example sites developed from the regional dimensionless rating curve are compared to stages predicted using gaging station rating curves with flow estimates given by the gaging station flow frequency data and the other flow estimation methods. The dimensionless rating curve stage method was generally superior in predicting stage than the flow estimation method. However, the dimensionless rating curve stage method provided better match to the flow frequency analyses stage estimation in the four example sites. Best performances in stage prediction are obtained by bankfull geometry regressions.