Figure IV.2-6. DSM2 results on the source water and salinity (“volumetric and constituent fingerprints) for the period November 2004 to February 2005. Reproduced from DWR (2005). Current DWR DPLA weekly report identifies individual sources of salt. A reasonable range of drainage salinity could be used to quantify part of the uncertainty. Ted Swift will talk more on this later on.

Modeling Issues with In-Delta Agricultural Uses Drainage salinity Drainage volume Net depletion

Figure IV.2-1. Approximate sampling locations of agricultural drainage salinity by DWR's Municipal Water Quality Investigation Program, data collected between 1986 and 1997. Data available at http://wdl.water.ca.gov/wq-gst/

Figure IV.2-2. Agricultural drainage salinity in south and southeast Delta. Drainage salinity at different pump stations on the same island (e.g. Kings Island) could be significantly different. Same symbol is used for different drainage pumps on the same island. Is it the island or is it the source water? Kings Island is low because of ESS? What about Empire Tract also on the east side? It’s all over the map. SJR water on one side and ESS on the other? Pescadero is high because of SJR? Woodward and Bacon are low because of the “through-Delta” flow from Sacramento?

Figure IV.2-5. Model input and recent measurements of agricultural drainage salinity in the Delta. Caveat: Not meant to be representative. This comparison is driven entirely by the data available.

Observations Wide scatter of drainage salinity: between islands between years between months Model input could be significantly different from field measurements Source tracking could be a solution Wide scatter of drainage salinity: from island to island (and even on same island) from year to year (Is hydrology a key factor?) from month to month Model input could be significantly different from field measurements. With the large number of drainage pumps in the Delta, each with uncertain volume of discharge, it would be impossible to obtain a reliable estimate. Would tracking the salt load from Delta islands be a feasible approach?

Issues Drainage salinity Drainage volume Net depletion Uncertainty between two studies 40 years apart.

1954, 1955 estimates made by DWR; 1995, 1996 by USGS; both estimates are based on power use and pump test data. Part of the difference between years may be due to difference in rainfall. Differences in drainage volumes in the summer, however, could be indicative of different crop types, irrigation pattern, or uncertainty in estimates. WY Sac SJR 1954 – AN BN 1955 – D D 1995 – W W 1996 – W W Jung, M. And Q. Tran. 1998. Delta island drainage volume estimates, 1954-1955 versus 1995-1996. Report to DWR, MWQI Program.

Jung, M. And Q. Tran. 1998. Delta island drainage volume estimates, 1954-1955 versus 1995-1996. Report to DWR, MWQI Program. Location definition for following graph

Factors: rain, need for leaching, seepage, amount of applied water and crop types Considerable difference. Is it the methodology? Or is it intrinsic variation? Or both? Is it a realistic goal to strive for “a” number? Jung, M. And Q. Tran. 1998. Delta island drainage volume estimates, 1954-1955 versus 1995-1996. Report to DWR, MWQI Program.

Issues Drainage salinity Drainage volume Net depletion An overview of the magnitude of the implication.

Huge difference in Rock Slough chloride concentration for a difference of 500 cfs at steady state.

Observations Drainage salinity Highly variable (season, island, year) Higher salinity assumed in model Drainage volume Large difference in 2 field estimates Net depletion Uncertainty of even a few hundred cfs could lead to large difference in simulated salinity