Implementing an Operational Framework to Develop a Streamflow Duration Assessment Method: A Case Study from the Arid West United States.

Gabrielle C. L. David,Ken M. Fritz,Robert Leidy,Rachel A. Harrington,Whitney S. Beck,Kenneth S. McCune,James T. Robb,Brian J. Topping,Julia E. Kelso,Aaron O. Allen,Tracie-Lynn Nadeau,Raphael D. Mazor

doi:10.3390/w13223310

Abstract

Streamflow duration information underpins many management decisions. However, hydrologic data are rarely available where needed. Rapid streamflow duration assessment methods (SDAMs) classify reaches based on indicators that are measured in a single brief visit. We evaluated a proposed framework for developing SDAMs to develop an SDAM for the Arid West United States that can classify reaches as perennial, intermittent, or ephemeral. We identified 41 candidate biological, geomorphological, and hydrological indicators of streamflow duration in a literature review, evaluated them for a number of desirable criteria (e.g., defensibility and consistency), and measured 21 of them at 89 reaches with known flow durations. We selected metrics for the SDAM based on their ability to discriminate among flow duration classes in analyses of variance, as well as their importance in a random forest model to predict streamflow duration. This approach resulted in a "beta" SDAM that uses five biological indicators. It could discriminate between ephemeral and non-ephemeral reaches with 81% accuracy, but only 56% accuracy when distinguishing 3 classes. A final method will be developed following expanded data collection. This Arid West study demonstrates the effectiveness of our approach and paves the way for more efficient development of scientifically informed SDAMs.

Highlights

Streamflow duration drives biodiversity patterns and ecosystem functions in stream reaches and their adjacent riparian zones, and knowledge of a reach’s streamflow duration may be used to inform a wide range of management decisions, such as determining applicable water quality standards or setting goals for restoration efforts [1]
We evaluated the number of instances where the change would correct a misclassification, and the number of times it would introduce a misclassification
We found that biological indicators were useful because of their ability to reflect long-term patterns in streamflow duration exhibited at a site

Summary

Introduction

Streamflow duration drives biodiversity patterns and ecosystem functions in stream reaches and their adjacent riparian zones, and knowledge of a reach’s streamflow duration may be used to inform a wide range of management decisions, such as determining applicable water quality standards or setting goals for restoration efforts [1]. Accurate characterization of streamflow duration requires long-term hydrologic data, which is typically only available at a relatively small number of gaged reaches [2,3]. Hydrologic models typically lack the ability to distinguish between ephemeral and intermittent reaches (due to the scarcity of gaged ephemeral reaches), and models based on gages with undisturbed catchments may not apply to reaches with altered hydrology [1]. Even without these limitations, managers would still need empirical methods to validate predictions from hydrologic models at ungagged reaches. Resource managers and researchers need rapid methods to assess streamflow duration at the reach scale where long-term data are unavailable; streamflow duration assessment methods (SDAMs) meet this need

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