Influence of Stage Discharge Relationship on the Annual Maximum Discharge Statistics

Discharge data are traditionally derived from measures of watersurface levels using stage-discharge relationships. Astage-discharge relation is obtained from direct dischargemeasurements for a set of water surface levels by fitting anempirical relationship to the data set. Since discharge measuresare made only for low flow conditions, the historicalstage-discharge relationships can give rise to severemisinterpretation for high flow values. The present work analysisthe influence on discharge statistics of the rating curve errorsfor the Liguria region. The work shows that historicalstage-discharge relations are highly uncertain when used for theestimation of annual maximum discharge. Moreover, data produced bythe traditional stage discharge relationships when compared withdata derived from more reliable theoretical stage-dischargerelationships, have statistically important biases. The findinghighlights a new problem in the use of historical data for floodrisk assessment.