Zero or not? Causes and consequences of zero‐flow stream gage readings
Citation:
Zimmer, M., K. Kaiser, J. Blaszcak, S. Zipper, J. Hammond, K. Fritz, K. Costigan, J. Hosen, S. Godsey, G. Allen, S. Kampf, R. Burrows, C. Krabbenhoft, W. Dodds, R. Hale, J. Olden, M. Shanafield, A. DelVecchia, A. Ward, M. Mims, T. Datry, M. Bogan, K. Boersma, M. Busch, C. Jones, A. Burgin, AND D. Allen. Zero or not? Causes and consequences of zero‐flow stream gage readings. WIREs Water. John Wiley & Sons, Inc., Hoboken, NJ, 7(3):e1436, (2020). https://doi.org/10.1002/wat2.1436
Impact/Purpose:
Hydrological measurement networks are critical to monitoring and predicting floods and allocating resources to support human and ecosystem water needs. Despite most gages being located on perennial streams, the prevalence of zero-flow measurements provides an opportunity to use existing gaging networks to describe and understand the hydrology of non-perennial streams. However, gages and their configuration were designed primarily for flood risk and human water consumption, and not for accurately documenting when and where streams drying occurs. In fact, there are multiple scenarios that can be associated with zero-flow gage readings besides stream drying. This paper presents a set of scenarios for how zero-flow gage readings may misrepresent flow conditions at local or network scales. For each scenarios, examples are provided from USGS gage stations, US field research stations, and international gage networks, and the authors present possible catchment or aquatic system indicators that can be used in conjunction with flow observations to determine if the gage readings are accurately representing the hydrologic system.
Description:
Streamflow observations can be used to understand, predict, and contextualize hydrologic, ecological, and biogeochemical processes and conditions in streams. Stream gages are point measurements along rivers where streamflow is measured, and are often used to infer upstream watershed‐scale processes. When stream gages read zero, this may indicate that the stream has dried at this location; however, zero‐flow readings can also be caused by a wide range of other factors. Our ability to identify whether or not a zero‐flow gage reading indicates a dry fluvial system has far reaching environmental implications. Incorrect identification and interpretation by the data user can lead to inaccurate hydrologic, ecological, and/or biogeochemical predictions from models and analyses. Here, we describe several causes of zero‐flow gage readings: frozen surface water, flow reversals, instrument error, and natural or human‐driven upstream source losses or bypass flow. For these examples, we discuss the implications of zero‐flow interpretations. We also highlight additional methods for determining flow presence, including direct observations, statistical methods, and hydrologic models, which can be applied to interpret causes of zero‐flow gage readings and implications for reach‐ and watershed‐scale dynamics. Such efforts are necessary to improve our ability to understand and predict surface flow activation, cessation, and connectivity across river networks. Developing this integrated understanding of the wide range of possible meanings of zero‐flows will only attain greater importance in a more variable and changing hydrologic climate.
