The last post about risk to Delta smelt was on January 9. Adult smelt migrate into the Delta from the Bay in winter to spawn. They take advantage of the flood tide to move upstream. However, with flood flows as high as 100,000 cfs entering the north Delta from the Sacramento River, the Yolo Bypass, and Georgiana Slough in mid- to late January 2017, there are no flood tides to ride into the north Delta spawning areas.
The only option for the adult smelt is thus to ride the incoming tide up the San Joaquin River into the central and south Delta (Figure 1). South Delta export pumping is currently at 14,000 cfs, near maximum capacity, using four rarely used auxiliary pumps. This pumping increases the pull of the incoming tide, reducing the effect of the inflow from the San Joaquin, Calaveras, Mokelumne, and Cosumnes rivers. While Delta inflow from these rivers is relatively high (Figures 2-5), it does not offset the influence of the incoming tide as does the inflow from the Sacramento.
Net tidal flows in lower Old and Middle Rivers (OMR flows) remain at the allowed limit of -5000 cfs, consistent with the smelt Biological Opinion. Several adult Delta smelt were salvaged at the export facilities in mid-January. 1 This scenario is considered a “high risk” to Delta smelt by the Smelt Working Group, because of the continuing risk that the pumps will draw or attract adult smelt into the central Delta and subsequently into the south Delta.
Under lower San Joaquin River flows, the maximum allowed export pumping is 11,400 cfs. High San Joaquin River inflow allows exports of 14,000 cfs that do not generate OMR flows more negative than -5000 cfs. The theoretical benefit of high San Joaquin River flows is that it should keep flow into the central and south Delta moving westward. But a large portion of that inflow is diverted south into the Head of Old River toward the pumping plants (Figure 6).
- https://www.usbr.gov/mp/cvo/vungvari/dsmeltsplitdly.pdf Note: website has changed to this new site. ↩