A DECISION-SUPPORT SYSTEM FOR THE ANALYSIS AND USE OF STAGE-DISCHARGERATING CURVES

A decision support system for fitting stage-discharge relations is bei ng developed by the University of Manitoba, Facility for Intelligent D ecision Support, for Environment Canada's hydrometric program. The pro cess of developing and applying stage-discharge relationships has been documented, the decision support system framework established, and a number of expert 'rules' developed and evaluated for stable and non-st able channels. The system categorizes stage-discharge rating curves as stable if they deviate within a predetermined accuracy (e.g. +/- 5% o f discharge), or if one of a suite of curves can be applied within the predetermined accuracy specifications for given changes in the energy slope caused by weed growth, channel ice and other conditions affecti ng backwater. Non-stable channels are defined as channels that experie nce evolution or abrupt changes in stage-discharge relationships resul ting from changes in channel form. Rating curve stability is determine d based on deviations in the stage-discharge relationship, utilizing s pecific gauge, absolute differences between sequential streamflow meas urements and an analysis of residuals. Periods of instability, such as a meander cut-off changing the hydraulic control, are often repetitiv e in hydraulic response, such that a pattern of instability is recogni zable as events occur. In addition, periods of instability are intersp ersed with periods of stability. The repetition in pattern allows know ledge of correctly identified historic events to be applied to contemp orary hydraulic conditions. A suite of rating curves can be developed for specific periods (e.g. summer weed growth) and stages. These curve s can be automatically applied based on changing streamflow conditions such that streamflow estimates can be generated in a rigorous and acc urate manner with minimal hydrographer intervention.