Our goal was to describe relationships between ecological condition and streamflow characteristics to support a stakeholder-driven assessment of hydrologic and ecological status in selected river basins of Colorado. All data were sourced from existing literature (> 100 studies) that described biota under specific flow conditions (annual peak flow and/or annual low flow). We derived relationships between individual flow metrics and four biotic groups: riparian vegetation, stream invertebrates, warm-water fish and salmonids.  Derived relationships were stratified for streams in the Rocky Mountains, Great Plains and Western Interior, as the three major hydroclimatic regions of the state.  The data were standardized (e.g., percent alteration, specific discharge), and then quantile regression was performed to distinguish the effect of flow from unmeasured limiting factors (typically 90% quantile).

This Watershed Flow Evaluation Tool was developed as a specific application under the broader framework of ELOHA (Ecological Limits of Hydrologic Alteration). This framework produced a defensible screening tool that can be applied regionally using estimates of hydrological alteration. Identifying streams where biota are most at risk from hydrological alteration has many applications, including prioritizing site-specific studies.