Apparent Seasonal Bias in Delta Outflow Estimates as Revealed in the Historical Salinity Record of the San Francisco Estuary: Implications for Delta Net Channel Depletion Estimates
Accurate estimates of freshwater flow to the San Francisco Estuary are important in successfully regulating this water body, in protecting its beneficial uses, and in accurately modeling its hydrodynamic and water-quality transport regime. For regulatory purposes, freshwater flow to the estuary is n...
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ftcdlib:oai:escholarship.org:ark:/13030/qt5bf4q1pt 2023-05-15T16:00:31+02:00 Apparent Seasonal Bias in Delta Outflow Estimates as Revealed in the Historical Salinity Record of the San Francisco Estuary: Implications for Delta Net Channel Depletion Estimates Hutton, Paul H. Rath, John S. Ateljevich, Eli S. Roy, Sujoy B. 2021-01-01 application/pdf https://escholarship.org/uc/item/5bf4q1pt unknown eScholarship, University of California qt5bf4q1pt https://escholarship.org/uc/item/5bf4q1pt CC-BY CC-BY San Francisco Estuary and Watershed Science, vol 19, iss 4 Sacramento–San Joaquin Delta outflow bias net channel depletion salinity empirical model article 2021 ftcdlib 2021-12-20T18:19:21Z Accurate estimates of freshwater flow to the San Francisco Estuary are important in successfully regulating this water body, in protecting its beneficial uses, and in accurately modeling its hydrodynamic and water-quality transport regime. For regulatory purposes, freshwater flow to the estuary is not directly measured; rather, it is estimated from a daily balance of upstream Delta inflows, exports, and in-Delta water use termed the net Delta outflow index (NDOI). Field research in the 1960s indicated that NDOI estimates are biased low in summer–fall and biased high in winter–spring as a result of conflating Delta island evapotranspiration estimates with the sum of ungauged hydrologic interactions between channels and islands referred to as net channel depletions. In this work, we employed a 50-year observed salinity record along with gauged tidal flows and an ensemble of five empirical flow-salinity (X2) models to test whether a seasonal bias in Delta outflow estimates could be inferred. We accomplished this objective by conducting statistical analyses and evaluating whether model skill could be improved through seasonal NDOI flow adjustments. Assuming that model residuals are associated with channel depletion uncertainty, our findings corroborate the 1960s research and suggest that channel depletions are biased low in winter months (i.e., NDOI is biased high) and biased high in late summer and early fall months (i.e., NDOI is biased low). The magnitude of seasonal bias, which can reach 1,000 cfs, is a small percentage of typical winter outflow but represents a significant percentage of typical summer outflow. Our findings were derived from five independently developed models, and are consistent with the physical understanding of water exchanges on the islands. This work provides motivation for improved characterization of these exchanges to improve Delta outflow estimates, particularly during drought periods when water supplies are scarce and must be carefully managed. Article in Journal/Newspaper Delta Island University of California: eScholarship |
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Open Polar |
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University of California: eScholarship |
op_collection_id |
ftcdlib |
language |
unknown |
topic |
Sacramento–San Joaquin Delta outflow bias net channel depletion salinity empirical model |
spellingShingle |
Sacramento–San Joaquin Delta outflow bias net channel depletion salinity empirical model Hutton, Paul H. Rath, John S. Ateljevich, Eli S. Roy, Sujoy B. Apparent Seasonal Bias in Delta Outflow Estimates as Revealed in the Historical Salinity Record of the San Francisco Estuary: Implications for Delta Net Channel Depletion Estimates |
topic_facet |
Sacramento–San Joaquin Delta outflow bias net channel depletion salinity empirical model |
description |
Accurate estimates of freshwater flow to the San Francisco Estuary are important in successfully regulating this water body, in protecting its beneficial uses, and in accurately modeling its hydrodynamic and water-quality transport regime. For regulatory purposes, freshwater flow to the estuary is not directly measured; rather, it is estimated from a daily balance of upstream Delta inflows, exports, and in-Delta water use termed the net Delta outflow index (NDOI). Field research in the 1960s indicated that NDOI estimates are biased low in summer–fall and biased high in winter–spring as a result of conflating Delta island evapotranspiration estimates with the sum of ungauged hydrologic interactions between channels and islands referred to as net channel depletions. In this work, we employed a 50-year observed salinity record along with gauged tidal flows and an ensemble of five empirical flow-salinity (X2) models to test whether a seasonal bias in Delta outflow estimates could be inferred. We accomplished this objective by conducting statistical analyses and evaluating whether model skill could be improved through seasonal NDOI flow adjustments. Assuming that model residuals are associated with channel depletion uncertainty, our findings corroborate the 1960s research and suggest that channel depletions are biased low in winter months (i.e., NDOI is biased high) and biased high in late summer and early fall months (i.e., NDOI is biased low). The magnitude of seasonal bias, which can reach 1,000 cfs, is a small percentage of typical winter outflow but represents a significant percentage of typical summer outflow. Our findings were derived from five independently developed models, and are consistent with the physical understanding of water exchanges on the islands. This work provides motivation for improved characterization of these exchanges to improve Delta outflow estimates, particularly during drought periods when water supplies are scarce and must be carefully managed. |
format |
Article in Journal/Newspaper |
author |
Hutton, Paul H. Rath, John S. Ateljevich, Eli S. Roy, Sujoy B. |
author_facet |
Hutton, Paul H. Rath, John S. Ateljevich, Eli S. Roy, Sujoy B. |
author_sort |
Hutton, Paul H. |
title |
Apparent Seasonal Bias in Delta Outflow Estimates as Revealed in the Historical Salinity Record of the San Francisco Estuary: Implications for Delta Net Channel Depletion Estimates |
title_short |
Apparent Seasonal Bias in Delta Outflow Estimates as Revealed in the Historical Salinity Record of the San Francisco Estuary: Implications for Delta Net Channel Depletion Estimates |
title_full |
Apparent Seasonal Bias in Delta Outflow Estimates as Revealed in the Historical Salinity Record of the San Francisco Estuary: Implications for Delta Net Channel Depletion Estimates |
title_fullStr |
Apparent Seasonal Bias in Delta Outflow Estimates as Revealed in the Historical Salinity Record of the San Francisco Estuary: Implications for Delta Net Channel Depletion Estimates |
title_full_unstemmed |
Apparent Seasonal Bias in Delta Outflow Estimates as Revealed in the Historical Salinity Record of the San Francisco Estuary: Implications for Delta Net Channel Depletion Estimates |
title_sort |
apparent seasonal bias in delta outflow estimates as revealed in the historical salinity record of the san francisco estuary: implications for delta net channel depletion estimates |
publisher |
eScholarship, University of California |
publishDate |
2021 |
url |
https://escholarship.org/uc/item/5bf4q1pt |
genre |
Delta Island |
genre_facet |
Delta Island |
op_source |
San Francisco Estuary and Watershed Science, vol 19, iss 4 |
op_relation |
qt5bf4q1pt https://escholarship.org/uc/item/5bf4q1pt |
op_rights |
CC-BY |
op_rightsnorm |
CC-BY |
_version_ |
1766396504634818560 |