Evaluating uncertainty in maximum flood flow estimated from hydrometric data for southern Québec basins

In general, streamflow is one of the hydrometric data required for characterizing flood hazard risk and thus for mapping flood-prone areas. These flows are estimated using a rating curve that relates water level to flow rate for a given watercourse. However, the uncertainties associated with the use of rating curves are not well known, particularly when the levels or flows are higher than those measured for the creation of the curve, as is the case for annual maximum flood flow used to identify return periods. Consequently, the quantification of uncertainty is crucial for proper estimation of flood-risk areas.

Photo : Direction de l’expertise hydrique (DEH) 

Develop a methodology for quantifying uncertainties in flow values estimated from rating curves and in the extreme flow quantiles estimated from maximum annual flow series at hydrometric stations in southern Québec. Particular attention will be paid to the uncertainty of extrapolation of rating curves beyond the range of gauged flows.

• Review of methods proposed in the literature in order to build a methodology based on the most appropriate approaches (gauging instrumentation, hydraulics, rating curve estimation, geomorphological changes, flow extrapolation);

• Documentation of approaches involving field visits currently used by the MELCC’s Direction de l’expertise hydrique;

• Collection, structuring and preliminary processing of data;

• Integration of sources of uncertainty (identified in the literature review) in flow estimation;

• Development of an uncertainty model for level and flow measurements applicable to all gauging sites in southern Québec.

• The project will provide a critical review of available methodologies relevant to Québec and an estimate of uncertainties in extreme flow values for different return periods at all gauged sites in southern Québec.

• An uncertainty model for flow measurements and extreme flow quantiles applicable to all gauging sites in southern Québec will be created.

• The project will also lead to the development of a core of expertise in hydraulics, hydrology and statistics relating to rating curves.