{"id":2806,"date":"2019-09-11T19:02:04","date_gmt":"2019-09-12T02:02:04","guid":{"rendered":"http:\/\/calsport.org\/fisheriesblog\/?p=2806"},"modified":"2019-09-11T19:02:04","modified_gmt":"2019-09-12T02:02:04","slug":"delta-outflow-measurement","status":"publish","type":"post","link":"https:\/\/calsport.org\/fisheriesblog\/?p=2806","title":{"rendered":"Delta Outflow Measurement"},"content":{"rendered":"

Delta outflow has been estimated by state and federal agencies for over 50 years.\u00a0 The Department of Water Resource\u2019s Delta Total Outflow is a daily-average algorithm calculated in cubic feet per second (cfs) for Station DTO<\/a>, a hypothetical location near Chipps Island in Suisun Bay.\u00a0 The federal Bureau of Reclamation\u2019s Delta Outflow estimate is calculated similarly and presented as a daily average flow in cubic feet per second on Reclamation\u2019s website<\/a>.<\/p>\n

Now a third estimate of Delta Outflow is available from the federal US Geological Survey on one of its websites (https:\/\/waterdata.usgs.gov\/nwis\/inventory?agency_code=USGS&site_no=380245121532301<\/a>).\u00a0 This site has daily average estimates for a \u201cgage\u201d near Chipps Island since summer of 2016.\u00a0 The estimate is from tidally filtered flow\/stage data.<\/p>\n

A comparison of the DWR and USGS estimates is shown below in Figures 1 and 2.\u00a0 The two estimates are very similar.\u00a0 A closer comparison during the low-flow summer periods of 2018 (Figure 3) and 2019 (Figure 4) indicates significant differences, or at a minimum a modicum of uncertainty in one or both of the estimates.\u00a0 The average flow in the DWR data for 2018 data is about 10% higher over the period than the USGS data.\u00a0 The role of tides or tidal filtering in the USGS estimate is a likely factor in the difference.\u00a0 Under high seasonal tide periods (termed spring tides), outflows can fall to near zero, with major ramifications to salinity and water over the entire Bay-Delta, especially in the high export summer season.<\/p>\n

The state\u2019s current water quality control plan for the Delta includes objectives for Delta outflow (Figure 5).\u00a0 The objectives are stated as a monthly average.\u00a0 The low level of the objectives 3000-8000 cfs should give one pause as to the level of protection that these objectives provide to public trust resources like fish.\u00a0 The Water Resources Control Board<\/a> is in the process of updating its plan and water quality objectives.<\/p>\n

In past posts<\/a>, I have advocated for daily salinity standards for the Delta rather than bi-weekly or monthly objectives for outflow, flow, export, and salinity.\u00a0 Such daily standards could be readily planned for, managed, monitored, and assessed for effectiveness.<\/p>\n

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Figure 1. USGS estimate daily Delta outflow Sep 2016 to Sep 2019.<\/p><\/div>\n

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Figure 2. DWR estimated daily Delta outflow Sep 2016 to Sep 2019.<\/p><\/div>\n

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Figure 3. Estimated daily outflow by DWR and USGS summer 2018.<\/p><\/div>\n

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Figure 4. Estimated daily outflow by DWR and USGS summer 2019.<\/p><\/div>\n

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Figure 5. Delta outflow objectives in state\u2019s water quality control plan.<\/p><\/div>\n","protected":false},"excerpt":{"rendered":"

Delta outflow has been estimated by state and federal agencies for over 50 years.\u00a0 The Department of Water Resource\u2019s Delta Total Outflow is a daily-average algorithm calculated in cubic feet per second (cfs) for Station DTO, a hypothetical location near … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[15,12],"tags":[],"class_list":["post-2806","post","type-post","status-publish","format-standard","hentry","category-bay-delta","category-water-quality"],"jetpack_featured_media_url":"","jetpack-related-posts":[],"jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/calsport.org\/fisheriesblog\/index.php?rest_route=\/wp\/v2\/posts\/2806","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/calsport.org\/fisheriesblog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/calsport.org\/fisheriesblog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/calsport.org\/fisheriesblog\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/calsport.org\/fisheriesblog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2806"}],"version-history":[{"count":1,"href":"https:\/\/calsport.org\/fisheriesblog\/index.php?rest_route=\/wp\/v2\/posts\/2806\/revisions"}],"predecessor-version":[{"id":2812,"href":"https:\/\/calsport.org\/fisheriesblog\/index.php?rest_route=\/wp\/v2\/posts\/2806\/revisions\/2812"}],"wp:attachment":[{"href":"https:\/\/calsport.org\/fisheriesblog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2806"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/calsport.org\/fisheriesblog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2806"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/calsport.org\/fisheriesblog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2806"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}