Last week, the court approved a joint stipulation (PDF) filed by the various parties involved in the OCAP salmonid litigation.  The stipulation will set the plan for the coordinated operation of the state and federal projects — striking some sort of balance between Delta exports and species protection, and replacing certain requirements of the biological opinion that Judge Wanger ordered last year be rewritten. The replacement plan will be in effect for the window of time from April 1 to May 31 of this year.
The two most notable characteristics of the agreement are elimination of the San Joaquin inflow-to-export ratio and revival of the spring Head of Old River barrier (HORB), a rock barrier installed at the confluence of Old River and the San Joaquin.  The agreement also sets allowable ranges for negative (reverse) flows in Old and Middle Rivers (OMR) induced by the southern Delta pumping plants and outlines a procedure describing how the desired flows can be adjusted adaptively. This procedure is apparently aimed at increasing transparency and cajoling NMFS into considering water supply impacts before making decisions.
The goal of the spring HORB is to provide additional protection for steelhead moving through the Delta from the San Joaquin Valley by directing fish down the San Joaquin channel and away from Old River. NMFS data suggests that the survival rate of salmonids moving through the Delta via the San Joaquin channel is roughly double that of salmonids that select the Old River route. The data also suggests that survival of salmonids using the San Joaquin channel improves when flows in that channel are higher (PDF).
A 2007 order issued by Judge Wanger prevented installation of the spring HORB because it amplified the negative OMR flows, endangering delta smelt during the springtime period in which the biological opinions imposed export restrictions to protect both delta smelt and salmonids. Although the Bureau’s Bio-Acoustic Fish Fence installed at the confluence has seen some success in directing salmonids away from Old River, this non-physical barrier does not direct additional flow into the mainstem San Joaquin. Construction of an operable gate has been previously proposed to replace the seasonal rock barrier in the future.
Because the spring HORB induces higher magnitude negative OMR flows, the HORB has been presented as one instance in which different species that use the Delta have conflicting and seemingly irreconcilable needs. However, an examination of the combined influence of exports and in-Delta diversions serves as a reminder of the profound effect that exports have on OMR flows, and that, depending on how one sets policies and priorities, the ostensibly conflicting needs of species could be balanced in a way that protects both delta smelt and salmonids, even with the HORB.
 Phase II of the inflow-to-export action, which would have been put into effect this spring, imposes ratios of 1:1 to 4:1 (increasing in wetter years) for inflow measured at Vernalis. Wanger’s opinion of this particular requirement was mixed. In 2011, he grudgingly acknowledged “marginal record support” for imposing an action taking the general form of a flow-export ratio, but he questioned whether the more strenuous 4:1 ratio in above normal and wet years was necessary.