Browsing by Author "Allen, George H."

Now showing 1 - 16 of 16
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    Assessing placement bias of the global river gauge network
    Krabbenhoft, Corey A.; Allen, George H.; Lin, Peirong; Godsey, Sarah E.; Allen, Daniel C.; Burrows, Ryan M.; DelVecchia, Amanda G.; Fritz, Ken M.; Shanafield, Margaret; Burgin, Amy J.; Zimmer, Margaret A.; Datry, Thibault; Dodds, Walter K.; Jones, C. Nathan; Mims, Meryl C.; Franklin, Catherin; Hammond, John C.; Zipper, Sam; Ward, Adam S.; Costigan, Katie H.; Beck, Hylke E.; Olden, Julian D. (Nature Portfolio, 2022-07)
    Hydrologic data collected from river gauges inform critical decisions for allocating water resources, conserving ecosystems and predicting the occurrence of droughts and floods. The current global river gauge network is biased towards large, perennial rivers, and strategic adaptations are needed to capture the full scope of rivers on Earth. Knowing where and when rivers flow is paramount to managing freshwater ecosystems. Yet stream gauging stations are distributed sparsely across rivers globally and may not capture the diversity of fluvial network properties and anthropogenic influences. Here we evaluate the placement bias of a global stream gauge dataset on its representation of socioecological, hydrologic, climatic and physiographic diversity of rivers. We find that gauges are located disproportionally in large, perennial rivers draining more human-occupied watersheds. Gauges are sparsely distributed in protected areas and rivers characterized by non-perennial flow regimes, both of which are critical to freshwater conservation and water security concerns. Disparities between the geography of the global gauging network and the broad diversity of streams and rivers weakens our ability to understand critical hydrologic processes and make informed water-management and policy decisions. Our findings underscore the need to address current gauge placement biases by investing in and prioritizing the installation of new gauging stations, embracing alternative water-monitoring strategies, advancing innovation in hydrologic modelling, and increasing accessibility of local and regional gauging data to support human responses to water challenges, both today and in the future.
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    Diminishing storage returns of reservoir construction
    Li, Yao; Zhao, Gang; Allen, George H.; Gao, Huilin (Nature Portfolio, 2023-06-13)
    Surface water reservoirs are increasingly being relied upon to meet rising demands in the context of growing population and changing climate. However, the amount of water available in reservoirs (and the corresponding trends) have not been well quantified at the global scale. Here we use satellite observations to estimate the storage variations of 7245 global reservoirs from 1999 to 2018. Total global reservoir storage has increased at a rate of 27.82 ± 0.08 km3/yr, which is mainly attributed to the construction of new dams. However, the normalized reservoir storage (NS)—the ratio of the actual storage to the storage capacity—has declined by 0.82 ± 0.01%. The decline of NS values is especially pronounced in the global south, while the global north mainly exhibits an NS increase. With predicted decreasing runoff and increasing water demand, these observed diminishing storage returns of reservoir construction will likely persist into the future.
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    Extending global river gauge records using satellite observations
    Riggs, Ryan M.; Allen, George H.; Wang, Jida; Pavelsky, Tamlin M.; Gleason, Colin J.; David, Cedric H.; Durand, Michael (IOP, 2023-05-26)
    Long-term, continuous, and real-time streamflow records are essential for understanding and managing freshwater resources. However, we find that 37% of publicly available global gauge records (N = 45 837) are discontinuous and 77% of gauge records do not contain real-time data. Historical periods of social upheaval are associated with declines in gauge data availability. Using river width observations from Landsat and Sentinel-2 satellites, we fill in missing records at 2168 gauge locations worldwide with more than 275 000 daily discharge estimates. This task is accomplished with a river width-based rating curve technique that optimizes measurement location and rating function (median relative bias = 1.4%, median Kling-Gupta efficiency = 0.46). The rating curves presented here can be used to generate near real-time discharge measurements as new satellite images are acquired, improving our capabilities for monitoring and managing river resources.
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    A Framework for Estimating Global River Discharge From the Surface Water and Ocean Topography Satellite Mission
    Durand, Michael; Gleason, Colin J.; Pavelsky, Tamlin M.; Frasson, Renato Prata de Moraes D. M.; Turmon, Michael; David, Cedric H.; Altenau, Elizabeth H.; Tebaldi, Nikki; Larnier, Kevin; Monnier, Jerome; Malaterre, Pierre Olivier; Oubanas, Hind; Allen, George H.; Astifan, Brian; Brinkerhoff, Craig; Bates, Paul D.; Bjerklie, David; Coss, Stephen; Dudley, Robert; Fenoglio, Luciana; Garambois, Pierre-Andre; Getirana, Augusto; Lin, Peirong; Margulis, Steven A.; Matte, Pascal; Minear, J. Toby; Muhebwa, Aggrey; Pan, Ming; Peters, Daniel; Riggs, Ryan; Sikder, Md Safat; Simmons, Travis; Stuurman, Cassie; Taneja, Jay; Tarpanelli, Angelica; Schulze, Kerstin; Tourian, Mohammad J.; Wang, Jida (American Geophysical Union, 2023-04-06)
    The Surface Water and Ocean Topography (SWOT) mission will vastly expand measurements of global rivers, providing critical new data sets for both gaged and ungaged basins. SWOT discharge products (available approximately 1 year after launch) will provide discharge for all river that reaches wider than 100 m. In this paper, we describe how SWOT discharge produced and archived by the US and French space agencies will be computed from measurements of river water surface elevation, width, and slope and ancillary data, along with expected discharge accuracy. We present for the first time a complete estimate of the SWOT discharge uncertainty budget, with separate terms for random (standard error) and systematic (bias) uncertainty components in river discharge time series. We expect that discharge uncertainty will be less than 30% for two-thirds of global reaches and will be dominated by bias. Separate river discharge estimates will combine both SWOT and in situ data; these “gage-constrained” discharge estimates can be expected to have lower systematic uncertainty. Temporal variations in river discharge time series will be dominated by random error and are expected to be estimated within 15% for nearly all reaches, allowing accurate inference of event flow dynamics globally, including in ungaged basins. We believe this level of accuracy lays the groundwork for SWOT to enable breakthroughs in global hydrologic science.
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    Inland Water Greenhouse Gas Budgets for RECCAP2: 1. State-Of-The-Art of Global Scale Assessments
    Lauerwald, Ronny; Allen, George H.; Deemer, Bridget R.; Liu, Shaoda; Maavara, Taylor; Raymond, Peter; Alcott, Lewis; Bastviken, David; Hastie, Adam; Holgerson, Meredith A.; Johnson, Matthew S.; Lehner, Bernhard; Lin, Peirong; Marzadri, Alessandra; Ran, Lishan; Tian, Hanqin; Yang, Xiao; Yao, Yuanzhi; Regnier, Pierre (American Geophysical Union, 2023-05-05)
    Inland waters are important emitters of the greenhouse gasses (GHGs) carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) to the atmosphere. In the framework of the 2nd phase of the REgional Carbon Cycle Assessment and Processes (RECCAP-2) initiative, we review the state of the art in estimating inland water GHG budgets at global scale, which has substantially advanced since the first phase of RECCAP nearly 10 years ago. The development of increasingly sophisticated upscaling techniques, including statistical prediction and process-based models, allows for spatially explicit estimates that are needed for regionalized assessments of continental GHG budgets such as those established for RECCAP. A few recent estimates also resolve the seasonal and/or interannual variability in inland water GHG emissions. Nonetheless, the global-scale assessment of inland water emissions remains challenging because of limited spatial and temporal coverage of observations and persisting uncertainties in the abundance and distribution of inland water surface areas. To decrease these uncertainties, more empirical work on the contributions of hot-spots and hot-moments to overall inland water GHG emissions is particularly needed.
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    Inland Water Greenhouse Gas Budgets for RECCAP2: 2. Regionalization and Homogenization of Estimates
    Lauerwald, R.; Allen, George H.; Deemer, B. R.; Liu, S.; Maavara, T.; Raymond, P.; Alcott, L.; Bastviken, D.; Hastie, A.; Holgerson, M. A.; Johnson, M. S.; Lehner, B.; Lin, P.; Marzadri, A.; Ran, L.; Tian, H.; Yang, X.; Yao, Y.; Regnier, P. (American Geophysical Union, 2023-05-10)
    Inland waters are important sources of the greenhouse gasses (GHGs) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) to the atmosphere. In the framework of the second phase of the REgional Carbon Cycle Assessment and Processes (RECCAP-2) initiative, we synthesize existing estimates of GHG emissions from streams, rivers, lakes and reservoirs, and homogenize them with regard to underlying global maps of water surface area distribution and the effects of seasonal ice cover. We then produce regionalized estimates of GHG emissions over 10 extensive land regions. According to our synthesis, inland water GHG emissions have a global warming potential of an equivalent emission of 13.5 (9.9–20.1) and 8.3 (5.7–12.7) Pg CO2-eq. yr−1 at a 20 and 100 years horizon (GWP20 and GWP100), respectively. Contributions of CO2 dominate GWP100, with rivers being the largest emitter. For GWP20, lakes and rivers are equally important emitters, and the warming potential of CH4 is more important than that of CO2. Contributions from N2O are about two orders of magnitude lower. Normalized to the area of RECCAP-2 regions, S-America and SE-Asia show the highest emission rates, dominated by riverine CO2 emissions.
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    Lake-TopoCat: a global lake drainage topology and catchment database
    Sikder, Md Safat; Wang, Jida; Allen, George H.; Sheng, Yongwei; Yamazaki, Dai; Song, Chunqiao; Ding, Meng; Cretaux, Jean-Francois; Pavelsky, Tamlin M. (Copernicus, 2023-08-08)
    Lakes and reservoirs are ubiquitous across global landscapes, functioning as the largest repository of liquid surface freshwater, hotspots of carbon cycling, and sentinels of climate change. Although typically considered lentic (hydrologically stationary) environments, lakes are an integral part of global drainage networks. Through perennial and intermittent hydrological connections, lakes often interact with each other, and these connections actively affect water mass, quality, and energy balances in both lacustrine and fluvial systems. Deciphering how global lakes are hydrologically interconnected (or the so-called "lake drainage topology") is not only important for lake change attribution but also increasingly critical for discharge, sediment, and carbon modeling. Despite the proliferation of river hydrography data, lakes remain poorly represented in routing models, partially because there has been no global-scale hydrography dataset tailored to lake drainage basins and networks. Here, we introduce the global Lake drainage Topology and Catchment database (Lake-TopoCat), which reveals detailed lake hydrography information with careful consideration of possible multifurcation. Lake-TopoCat contains the outlet(s) and catchment(s) of each lake; the interconnecting reaches among lakes; and a wide suite of attributes depicting lake drainage topology such as upstream and downstream relationship, drainage distance between lakes, and a priori drainage type and connectivity with river networks. Using the HydroLAKES v1.0 (Messager et al., 2016) global lake mask, Lake-TopoCat identifies ĝ1/4ĝ1.46 million outlets for ĝ1/4ĝ1.43 million lakes larger than 10ĝha and delineates 77.5×106ĝkm2 of lake catchments covering 57ĝ% of the Earth's landmass except Antarctica. The global lakes are interconnected by ĝ1/4ĝ3 million reaches, derived from MERIT Hydro v1.0.1 (Yamazaki et al., 2019), stretching a total distance of ĝ1/410×106ĝkm, of which ĝ1/4ĝ80ĝ% are shorter than 10ĝkm. With such unprecedented lake hydrography details, Lake-TopoCat contributes towards a globally coupled lake-river routing model. It may also facilitate a variety of limnological applications such as attributing water quality from lake scale to basin scale, tracing inter-lake fish migration due to changing climate, monitoring fluvial-lacustrine connectivity, and improving estimates of terrestrial carbon fluxes. Lake-TopoCat is freely accessible at 10.5281/zenodo.7916729 (Sikder et al., 2023).
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    Optimizing Satellite Mission Requirements to Measure Total Suspended Solids in Rivers
    Stroud, Molly K.; Allen, George H.; Simard, Marc; Jensen, Daniel; Gorr, Ben; Selva, Daniel (IEEE, 2023-11-29)
    Human modification of the landscape affects total suspended solid (TSS) concentrations in water. The quantitative extent of these changes remains poorly understood, partly because of the challenges associated with observing TSS dynamics in inland waters over large scales. While many current missions and sensors provide usable data to estimate inland water quality (e.g. Landsat series, VIIRS, and Sentinel-2), future missions present the opportunity to increase transferability and accuracy of TSS estimation. Here, we degrade assumed ideal spectral data to evaluate the optimal data quality for TSS retrieval using an optical sensor configuration. We also perform wavelet analysis and a river size distribution analysis to study temporal and spatial data quantity requirements, respectively. We find that while the highest resolution data always gives the best retrieval accuracy, some factors are more essential in TSS estimation than others and can simplify mission design. Specifically, fine hyperspectral resolution is key in improving retrieval accuracy and a finer spatial resolution allows exponentially more river surface area to be observed. A revisit period of approximately five days or less best captures TSS pulse events, such as floods. Understanding the optimal mission specifications for observing inland water quality, especially TSS, will assist in developing and proposing future optical satellite missions.
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    Pervasive changes in stream intermittency across the United States
    Zipper, Samuel C.; Hammond, John C.; Shanafield, Margaret; Zimmer, Margaret; Datry, Thibault; Jones, C. Nathan; Kaiser, Kendra E.; Godsey, Sarah E.; Burrows, Ryan M.; Blaszczak, Joanna R.; Busch, Michelle H.; Price, Adam N.; Boersma, Kate S.; Ward, Adam S.; Costigan, Katie; Allen, George H.; Krabbenhoft, Corey A.; Dodds, Walter K.; Mims, Meryl C.; Olden, Julian D.; Kampf, Stephanie K.; Burgin, Amy J.; Allen, Daniel C. (2021-08)
    Non-perennial streams are widespread, critical to ecosystems and society, and the subject of ongoing policy debate. Prior large-scale research on stream intermittency has been based on long-term averages, generally using annually aggregated data to characterize a highly variable process. As a result, it is not well understood if, how, or why the hydrology of non-perennial streams is changing. Here, we investigate trends and drivers of three intermittency signatures that describe the duration, timing, and dry-down period of stream intermittency across the continental United States (CONUS). Half of gages exhibited a significant trend through time in at least one of the three intermittency signatures, and changes in no-flow duration were most pervasive (41% of gages). Changes in intermittency were substantial for many streams, and 7% of gages exhibited changes in annual no-flow duration exceeding 100 days during the study period. Distinct regional patterns of change were evident, with widespread drying in southern CONUS and wetting in northern CONUS. These patterns are correlated with changes in aridity, though drivers of spatiotemporal variability were diverse across the three intermittency signatures. While the no-flow timing and duration were strongly related to climate, dry-down period was most strongly related to watershed land use and physiography. Our results indicate that non-perennial conditions are increasing in prevalence over much of CONUS and binary classifications of 'perennial' and 'non-perennial' are not an accurate reflection of this change. Water management and policy should reflect the changing nature and diverse drivers of changing intermittency both today and in the future.
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    Satellites reveal hotspots of global river extent change
    Wu, Qianhan; Ke, Linghong; Wang, Jida; Pavelsky, Tamlin M.; Allen, George H.; Sheng, Yongwei; Duan, Xuejun; Zhu, Yunqiang; Wu, Jin; Wang, Lei; Liu, Kai; Chen, Tan; Zhang, Wensong; Fan, Chenyu; Yong, Bin; Song, Chunqiao (Nature Portfolio, 2023-03-22)
    Rivers are among the most diverse, dynamic, and productive ecosystems on Earth. River flow regimes are constantly changing, but characterizing and understanding such changes have been challenging from a long-term and global perspective. By analyzing water extent variations observed from four-decade Landsat imagery, we here provide a global attribution of the recent changes in river regime to morphological dynamics (e.g., channel shifting and anabranching), expansion induced by new dams, and hydrological signals of widening and narrowing. Morphological dynamics prevailed in ~20% of the global river area. Booming reservoir constructions, mostly skewed in Asia and South America, contributed to ~32% of the river widening. The remaining hydrological signals were characterized by contrasting hotspots, including prominent river widening in alpine and pan-Arctic regions and narrowing in the arid/semi-arid continental interiors, driven by varying trends in climate forcing, cryospheric response to warming, and human water management. Our findings suggest that the recent river extent dynamics diverge based on hydroclimate and socio-economic conditions, and besides reflecting ongoing morphodynamical processes, river extent changes show close connections with external forcings, including climate change and anthropogenic interference.
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    Spatial Patterns and Drivers of Nonperennial Flow Regimes in the Contiguous United States
    Hammond, John C.; Zimmer, Margaret A.; Shanafield, Margaret; Kaiser, Kendra E.; Godsey, Sarah E.; Mims, Meryl C.; Zipper, Samuel C.; Burrows, Ryan M.; Kampf, Stephanie K.; Dodds, Walter K.; Jones, C. Nathan; Krabbenhoft, Corey A.; Boersma, Kate S.; Datry, Thibault; Olden, Julian D.; Allen, George H.; Price, Adam N.; Costigan, Katie H.; Hale, Rebecca; Ward, Adam S.; Allen, Daniel C. (2021-01-28)
    Over half of global rivers and streams lack perennial flow, and understanding the distribution and drivers of their flow regimes is critical for understanding their hydrologic, biogeochemical, and ecological functions. We analyzed nonperennial flow regimes using 540 U.S. Geological Survey watersheds across the contiguous United States from 1979 to 2018. Multivariate analyses revealed regional differences in no-flow fraction, date of first no flow, and duration of the dry-down period, with further divergence between natural and human-altered watersheds. Aridity was a primary driver of no-flow metrics at the continental scale, while unique combinations of climatic, physiographic and anthropogenic drivers emerged at regional scales. Dry-down duration showed stronger associations with nonclimate drivers compared to no-flow fraction and timing. Although the sparse distribution of nonperennial gages limits our understanding of such streams, the watersheds examined here suggest the important role of aridity and land cover change in modulating future stream drying. Plain Language Summary A majority of global streams are nonperennial, flowing only part of the year, and are critical for sustaining flow downstream, providing habitat for many organisms, and regulating chemical and biological processes. Using long-term U.S. Geological Survey measurements for 540 watersheds across the contiguous United States, we mapped patterns and examined the causes of no-flow fraction, the fraction of each climate year with no flow, no-flow timing, the date of the climate year on which the first recorded no flow takes place, and length of the dry-down period, the average number of days from a local peak in daily flow to the first occurrence of no flow. We found differences in patterns of no-flow characteristics between regions, with higher no-flow fraction, earlier timing, and shorter dry-down duration in the western United States. No-flow fractions were greater and less variable in natural watersheds, while no-flow timing was earlier and dry-down duration was shorter in human-modified watersheds. Aridity had the greatest effect on intermittence across the United States, but unique combinations of climate, biophysical, and human impacts were important in different regions. The number of gages measuring streamflow in nonperennial streams is small compared to perennial streams, and increased monitoring is needed to better understand drying behavior. Key Points . Three metrics reveal regional and human-driven patterns of nonperennial flow: no-flow fraction, day of first no flow, and dry-down duration Streams with human modifications generally dry more quickly than unmodified streams, especially in California and the Southern Great Plains Climate strongly influences no-flow fraction and timing, but physiographic variables are more important for the duration of dry down
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    Turning Lakes Into River Gauges Using the LakeFlow Algorithm
    Riggs, Ryan M.; Allen, George H.; Brinkerhoff, Craig B.; Sikder, Md. Safat; Wang, Jida (American Geophysical Union, 2023-05)
    Rivers and lakes are intrinsically connected waterbodies yet they are rarely used to hydrologically constrain one another with remote sensing. Here we begin to bridge the gap between river and lake hydrology with the introduction of the LakeFlow algorithm. LakeFlow uses river-lake mass conservation and observations from the Surface Water and Ocean Topography (SWOT) satellite to provide river discharge estimates of lake and reservoir inflows and outflows. We test LakeFlow performance at three lakes using a synthetic SWOT data set assuming the maximum measurement errors defined by the mission science requirements, and we include modeled lateral inflow and lake evaporation data to further constrain the mass balance. We find that LakeFlow produces promising discharge estimates (median Nash-Sutcliffe efficiency = 0.88, relative bias = 14%). LakeFlow can inform water resources management by providing global lake inflow and outflow estimates, highlighting a path for recognizing rivers and lakes as an interconnected system.
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    Using Water Quality as a Proxy to Estimate Microplastic Concentrations in the New River, VA, via Sentinel 2
    Rodriguez Sequeira, Luisana; Allen, George H.; Gray, Austin D. (New River Symposium, 2024-04-12)
    Microplastics (<5mm), are pervasive in Earth’s environments, and rivers are a major transport pathway. Microplastic detection methods that rely on counting individual particles are time consuming and require laborious field collection, inhibiting real-time insights over large spatial extents, which are needed in order to better understand the issue. Satellite remote sensing has been used to estimate water quality in rivers with relatively high spatial and temporal coverage. Finding a correlation between water quality and microplastics could allow us to estimate microplastics in rivers via satellite imagery using water quality as a proxy. Though a handful of these assessments have been done, a wide-variety of study sites are needed to form a coherent model. We focused our study in the New River near Blacksburg, VA, and collected weekly water quality measurements and surface-water microplastic samples. We combined these in situ measurements with cotemporal remotely-sensed water quality index observations from Sentinel-2 to develop a model estimating microplastic concentration. We validated the model using in-situ spectrometry and water quality measurements. By providing more observations than what can be done with in situ sampling alone, we can improve large-scale microplastic analyses and modeling leading to better assessments of mismanaged plastic waste in Earth’s rivers.
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    What’s in a Name? Patterns, Trends, and Suggestions for Defining Non-Perennial Rivers and Streams
    Busch, Michelle H.; Costigan, Katie H.; Fritz, Ken M.; Datry, Thibault; Krabbenhoft, Corey A.; Hammond, John C.; Zimmer, Margaret A.; Olden, Julian D.; Burrows, Ryan M.; Dodds, Walter K.; Boersma, Kate S.; Shanafield, Margaret; Kampf, Stephanie K.; Mims, Meryl C.; Bogan, Michael T.; Ward, Adam S.; Perez Rocha, Mariana; Godsey, Sarah E.; Allen, George H.; Blaszczak, Joanna R.; Jones, C. Nathan; Allen, Daniel C. (MDPI, 2020-07-13)
    Rivers that cease to flow are globally prevalent. Although many epithets have been used for these rivers, a consensus on terminology has not yet been reached. Doing so would facilitate a marked increase in interdisciplinary interest as well as critical need for clear regulations. Here we reviewed literature from Web of Science database searches of 12 epithets to learn (Objective 1—O1) if epithet topics are consistent across Web of Science categories using latent Dirichlet allocation topic modeling. We also analyzed publication rates and topics over time to (O2) assess changes in epithet use. We compiled literature definitions to (O3) identify how epithets have been delineated and, lastly, suggest universal terms and definitions. We found a lack of consensus in epithet use between and among various fields. We also found that epithet usage has changed over time, as research focus has shifted from description to modeling. We conclude that multiple epithets are redundant. We offer specific definitions for three epithets (non-perennial, intermittent, and ephemeral) to guide consensus on epithet use. Limiting the number of epithets used in non-perennial river research can facilitate more effective communication among research fields and provide clear guidelines for writing regulatory documents.
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    When does a stream become a river?
    Czuba, Jonathan A.; Allen, George H. (Wiley, 2023-07-13)
    The distinction between a “stream” and “river” is imprecise and vague despite the popular usage of the terms across disciplines for describing flowing waterbodies. Based on an analysis of named flowing waterbodies in the continental United States, we suggest a bank-to-bank channel width of 15 m as a working threshold in defining smaller “streams” from larger “rivers.”.
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    Zero or not? Causes and consequences of zero-flow stream gage readings
    Zimmer, Margaret A.; Kaiser, Kendra E.; Blaszczak, Joanna R.; Zipper, Samuel C.; Hammond, John C.; Fritz, Ken M.; Costigan, Katie H.; Hosen, Jacob; Godsey, Sarah E.; Allen, George H.; Kampf, Stephanie K.; Burrows, Ryan M.; Krabbenhoft, Corey A.; Dodds, Walter K.; Hale, Rebecca; Olden, Julian D.; Shanafield, Margaret; DelVecchia, Amanda G.; Ward, Adam S.; Mims, Meryl C.; Datry, Thibault; Bogan, Michael T.; Boersma, Kate S.; Busch, Michelle H.; Jones, C. Nathan; Burgin, Amy J.; Allen, Daniel C. (2020-05)
    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. This article is categorized under: Science of Water > Methods Science of Water > Hydrological Processes Water and Life > Conservation, Management, and Awareness