Central District collects, analyzes, and stores flow, stage, and tide information from rivers and streams throughout its district boundaries, as well as operating and maintaining a network of continuously monitoring tide stations in the Delta. Surface water conditions in the Delta are an issue of particular importance and data collected within the Delta is presented separate from the surface water information collected from other rivers and streams.

Datum Change in the Delta

In 2002, DWR conducted a Global Positioning System (GPS) survey of over 100 vertical control benchmarks in the Sacramento-San Joaquin Delta. The purpose of this survey was to improve the accuracy and usability of our surface water data collected by our network of tide monitoring stations. The data collected in the 2002 GPS survey was processed by the Department with assistance from the National Geodetic Survey. The vertical datum that our tide monitoring stations in the Delta are set to were updated during the summer of 2005 from the old National Geodetic Vertical Datum 29 (NGVD29) to the North American Vertical Datum 88 (NAVD88). This change in vertical datum impacts both State and local flood alert systems as well as hydrodynamic and environmental studies in the Delta. To eliminate potential confusion, the Department initiated a public outreach and education program to assist data users in transitioning from the old NGVD29 datum to the new NAVD88 datum. The Department fully adopted the NAVD88 datum standard on October 1, 2006.

Click here to view a detailed explanation of the datum change and how it may affect local water operation procedures.

Click here to view a map of the Delta and all of the Department's tide monitoring stations that were affected by this datum change:

Table 1 lists all of our Delta tide monitoring stations along with latitude/longitude and correction factors to convert from the NGVD29 to NAVD88.

The Change to the new NAVD88 datum will affect the tide stage forecasts for four Delta locations (Rio Vista, Antioch, Mallard Island and Venice Island) and river stage forecasts for three official river forecast points (Mokelumne River at Benson's Ferry near Thornton, San Joaquin River at Mossdale Bridge, and Yolo Bypass at Lisbon). In addition to affecting stage forecasts, the NAVD88 change requires modification to the monitor stage, flood stage, and danger stage values at four of these locations. Table 2 summarizes the datum changes for all seven of these stations.