A Look Inside The Data: Sacramento Saltwater Observations

Hello and welcome back to another post on The Deluge!  I wanted to write about salinity observations along the Sacramento and San Joaquin rivers as they supply California’s central valley with water.

The data I choose to share today comes from the Report of Sacramento-San Joaquin Water Supervision for Year 1940. Plate 2 from this report is a stylish map of the Sacramento-San Joaquin delta and adjacent uplands. Sacramento is to the north and south of Stockton is at the southeast of the map.  

Map of Sacramento and San Joaquin Rivers

Chapter 6 from Report of Sacramento-San Joaquin water supervision for year 1940, page 2 

This map shows us the salinity observation stations along the Sacramento and San Joaquin rivers. These rivers deliver water from the San Francisco Bay all the way to Sacramento and Stockton respectively; the salinity of the water plays a crucial role in determining the proper use of water. Too much salt content may damage the local crops. The report states that the salt content was measured at regular intervals between 1920 and 1940. 

The legend for the map indicates salinity stations with a clear, black dot. From the west, the Sacramento and San Joaquin rivers split off as the Sacramento River heads north and the San Joaquin River spreads east. The report states that there are 20 stations in the delta and uplands, but I counted around 40 stations on the map.  

The map also details salinity encroachment which is presented by a dotted line. This shows how far a higher level of salinity encroaches onto irrigated areas which are fed directly from the Sacramento and San Joaquin rivers. The total area is not that alarming, but to farmers and engineers without modern technology, I can imagine how useful this data would be.  


Making sure water coming from saltwater is safe for agricultural purposes is crucial for California’s economy. Hope you enjoy looking at this map and reading the report. I will be back next week with another post on The Deluge!