Hydrograph Shape Factor: A Robust Approach For Hydrologic Classification

A major challenge of past and recent hydrologic classification work has been selecting among the many possible metrics for use in the delineation of homogeneous hydrologic regions. Regional hydro-climatic classification based on the stream/river discharge of catchments can help reveal unique patterns governed by higher order controls such as climate and physiography, and provide valuable insights on how flow regimes differ across spatial and temporal scales without extensive data requirements. This work explores and tests an approach to classification based solely on the shape of hydrographs with the objective of exploring if shape factor can serve as a simplified, yet robust approach for regional hydrologic classification. Hierarchal cluster analysis of standardized hydrograph shape using long term streamflow records of small catchments (<1000 km2) distributed across the forested landbase of Alberta, Canada demonstrated that the province can be classified into six distinct hydrologic regions. Each region exhibited a unique flow regime (i.e. characteristically unique hydrograph shapes) that reflected the regional variation in hydro-climatic controls dominating streamflow response (physiography, topography, and climate). Further analysis among these regions using specific streamflow variables representative of the overall flow regime including; flow magnitude (mean annual streamflows, flow duration curves, mean maximum and minimum flows); timing of flows (timing of max/min flows, half flow dates), and extreme flows (flood frequency, number and duration of high and low flow events) indicated that the original classification based on shape factor was robust in separating regions of distinct hydrologic behaviour across these more detailed flow parameters. This range of unique flow characteristics reveals further insights into variation of surface water hydrology across Alberta's forested regions.