The Delta Corridors Plan will provide substantial improvements in fish protection and survival by modifying the fish migration pathways for both Sacramento River fish and SJR fish and by protecting the fish spawning and rearing habitat in Old River, Franks Tract and the lower SJR from entrainment risk. The Delta Corridors Plan will be effective if the existing SWRCB D-1641 objectives for minimum outflow, maximum salinity, maximum X2 and maximum export pumping remain applicable or if modified Delta objectives are implemented in the future. The existing objectives for CVP and SWP Delta operations are briefly summarized so that possible future modifications to the existing Delta objectives can be described and compared.
SWRCB Objectives for CVP and SWP Delta Operations
Delta objectives can be simplified into two sets of rules; (1) rules controlling the maximum allowable exports and (2) rules controlling the minimum required Delta outflow. Several different objectives are used to control the allowable exports and several more objectives are used to control the minimum required Delta outflow. The existing CVP and SWP Delta operations are determined by many applicable rules and objectives that control the daily Delta outflow and exports. Many of these rules are included in D-1641 (which implemented the 1995 Bay-Delta WQCP objectives). Several additional rules have been added by the 2008 USFWS Biological Opinion and the 2009 NMFS Biological Opinion for the CVP and SWP Operations Criteria and Plan (OCAP). The Delta objectives provide the answer to the important question: “How much of the Delta inflows can be exported at the south Delta CVP and SWP pumping plants, and how much of the Delta inflows must be left for Delta outflow?”
Maximum Allowable Export Rules
The first two rules govern the maximum CVP and SWP pumping capacities. The permitted CVP capacity is 4,600 cfs, which requires use of the new DMC-CA Intertie facility in the winter months. The existing SWP pumping capacity is constrained by the CCF diversion limit set by the USACE (Rivers and Harbors Section 10) of 6,680 cfs with additional diversions of 1/3 of the San Joaquin River flow at Vernalis between December 15 and March 15. The SWP Banks pumping plant physical capacity is 10,300 cfs.
The export/inflow ratio was introduced in the 1995 WQCP and limits the CVP and SWP combined pumping to 65% of the Delta inflow from July to January, and to 35% of the Delta inflow from February to June. The rule is applied with a 7-day moving average of inflow and a 3-day average of export pumping. The 35% is increased to 45% in February if the January runoff was low (D-1641).
The USFWS and NMFS Biological Opinions introduced new limits on the reverse (i.e., negative) OMR flow in the months of December-June. Reverse OMR flows are equal to the combined exports minus the head of Old River flow diverted from the SJR near Mossdale. OMR flows are adaptively managed based on fish monitoring. The OMR limits vary with fish and turbidity conditions; the maximum reverse OMR flow (i.e., maximum exports) are about 5,000 cfs for January-March. An additional export limit imposed by the 2009 NMFS Biological Opinion was an export/SJR inflow ratio in April and May. This ratio effectively limits the combined exports to 1,500 cfs for SJR inflows of less than 6,000 cfs.
The last constraint on Delta exports is related to the assumed water supply demands for south of Delta CVP and SWP contractors. The full CVP and SWP demands are about 7.5 million acre-feet (maf) and April-September demands are about 5 maf (2/3 of annual). The San Luis Reservoir provides about 2 maf of seasonal storage for meeting the peak summer water supply demands. The San Luis Reservoir storage allows exports that are higher than the demands in the fall and winter months. Exports are sometimes reduced in February-May once San Luis Reservoir is filled.
Minimum Required Delta Outflow Rules
The first set of rules that control Delta outflow are the D-1641 minimum outflow objectives for each month, which often depend on the water-year type (i.e., runoff conditions). For example, a minimum monthly outflow of 3,000 cfs is specified in September of all years. A minimum monthly outflow of 8,000 cfs is specified in July of wet and above normal water-year types (about half of the years).
The second set of rules that control Delta outflow are the maximum salinity objectives specified in D-1641 for some periods, which depend on the water-year type. For example, salinity (EC) objectives are specified at Emmaton and Jersey Point to protect agricultural diversions, and salinity (chloride) objectives are specified at the CCWD Rock Slough intake to protect drinking water supplies. Because Delta outflow is the major factor controlling salinity within the Delta, the salinity objectives are satisfied by reducing exports to increase Delta outflow when the Delta inflows are low. Estimates of the Delta outflow required to meet the salinity objectives have been determined by evaluating historical records of Delta outflow and salinity monitoring. For example, an outflow of 3,000 cfs would correspond to a Jersey Point EC of about 2,000 uS/cm, an outflow of 4,500 cfs would correspond to a Jersey Point EC of about 1,400 uS/cm and an outflow of 6,000 cfs would correspond to a Jersey Point EC of about 1,000 uS/cm.
The third set of rules that control Delta outflow are the spring X2 objectives introduced in the 1995 WQCP. The required location of the 2 ppt salinity upstream of the Golden Gate (kilometers) is specified, based on the month and the unimpaired runoff in the previous month. This was formulated as an adaptive objective; the required outflow increased with higher runoff conditions. D-1641 provides equivalent Delta outflows for the X2 objectives; X2 at Collinsville (81 km) can be satisfied with an outflow of 7,100 cfs and X2 at Chipps Island (75 km) can be satisfied with an outflow of 11,400 cfs. The 2008 USFWS Biological Opinion included an additional outflow requirement for September and October of wet and above normal water-year types (about half the years). The Fall X2 rule requires X2 to be downstream of Collinsville (7,100 cfs outflow) in above normal years and downstream of Chipps Island (11,400 cfs outflow) in wet years.
Additional Information about Future Delta Operations
Several reports about previous efforts to modify the Delta objectives to provide increased fish protection are given below. The USFWS and NMFS biological opinions introduced several additional measures to limit entrainment of Delta smelt and juvenile Chinook and to improve migration success for juvenile Chinook and steelhead. The major difficulty with proposing new Delta objectives or measures is that increases in Delta outflow to improve estuarine habitat will reduce Delta exports and reduce the available water supply. While the reduced water supply can be identified and quantified as economic impacts on agriculture, the benefits from improved fish habitat and increased fish migration success cannot be easily identified or quantified as increased adult fish abundance. Improved methods for tracking fish survival in the Delta and evaluating the effects of fish protection on the adult populations would allow more accurate balancing of Delta water supply and Delta fish benefits resulting from reduced exports and increased Delta outflows.
Should the Delta objectives be relaxed during dry and critical years with very limited Delta inflows? The D-1641 objectives are relaxed somewhat in dry and critical years, but the recent experience with Temporary Urgency Change Petitions (TUCP) in 2014 and 2015 suggest that changes in the objectives during drought conditions is difficult. This report suggests that reduced minimum Delta outflows and increased export objectives be considered to increase the water supply during drought years.
The SWRCB Delta objectives increase the minimum required Delta outflows or reduce the allowable exports to protect beneficial uses for fish and wildlife and for water supply (i.e., salinity control. This report describes the effects of each Delta objective on outflows and exports.
Delta operations in WY 2008 and 2009 were reviewed for this testimony at the SWRCB February 2010 Proceeding on Delta Flow Criteria. The evaluation of benefits for salinity, water supply and for fish from the Delta objectives for outflow, X2 and E/I are discussed. A monthly inflow allocation approach is suggested for balancing water supply, salinity and fish benefits.