One purpose of the Vernalis Adaptive Management Plan (VAMP), beyond looking at flows and exports, was to investigate how the survival rate of Chinook salmon smolts migrating through the San Joaquin River system could be improved by constructing a rock barrier at the Head of Old River (HORB). Reverse Old & Middle River (OMR) flows induced by state and federal project exports, as well as predators lurking in the South Delta, pose significant challenges for smolts that attempt to navigate through the Bay Delta Estuary to the Pacific Ocean. The smolts have a better chance of survival if they remain in the San Joaquin River channel; thus, one component of VAMP was to install the HORB in both the spring and the fall, to divert fish away from the Old River. In addition to directing fish toward safer migratory paths, another benefit of using a physical barrier is that it ushers higher flows into the San Joaquin channel, helping to ensure that smolts make their way past predators and through the estuary more swiftly.
Here is a map of the terrain with the barrier location labeled:
The HORB has no longer been constructed as of 2008, ostensibly for the protection of delta smelt (see discussion below). In order to increase salmon survival rates without installing a physical barrier, Reclamation has instead studied the Bio-Acoustic Fish Fence (BAFF). The BAFF is a non-physical barrier designed to discourage salmon from entering the Old River channel, by using LED strobe lighting, acoustic deterrents within a frequency range of 5-600 Hz, and a bubble curtain that contains the sounds generated. When placed on the San Joaquin River, just upstream of the confluence with Old River, the BAFF deterred a significant quantity of smolts (81.4%) from entering the Old River channel. Worth noting, however, is that while the the BAFF appears to direct most smolts away from the Old River, a non-physical barrier would not provide the benefit of increased flow in the San Joaquin channel, which a physical HORB would do.
Protecting delta smelt, or protecting exports?
On December 14, 2007, Judge Wanger issued an order that, among other things, prohibited construction of the spring HORB. The rationale is that the barrier directs migrating salmon — and the San Joaquin water carrying them — away from the Old River channel and into the San Joaquin channel, thereby diminishing the downstream (i.e. positive) Old River flow. Thus, as negative OMR flows are amplified, there is increased danger of delta smelt entrainment.
This observation is reflected in modeling done by Reclamation. The graphs below show a sample of the flow changes with and without barriers. They depict the first six months of the year, when OMR flows are monitored and adjusted in response to delta smelt entrainment levels at the project pumps. Note that these result aggregate HORB and agricultural barriers. In a wet year (1984):
And in a dry year (1989):
Thus, restrictions placed on the spring HORB are usually characterized as pitting one species against another: sacrificing increased salmon protection with the HORB, in order to protect delta smelt. The needs of these two species are quite different in many respects, and not always perfectly harmonious or compatible — a reality that the State Board is coming to terms with as it develops the flow criteria. Still, it’s not necessarily clear that this is a situation where the needs of different species must come into conflict. In its natural state, of course, the estuary supported both species.
Consider these regression equations, which are valid for lower flows measured at Vernalis consistent with VAMP conditions. The equations express OMR flows in terms of state/federal project exports and Vernalis flows (all measured in cubic feet per second). To be more accurate, we can also include Contra Costa Water District (CCWD) diversions from Old River, and agricultural diversions and drainage in the South Delta. With the spring HORB:
And without the HORB:
Fish and Wildlife tells us that the trick is to protecting larval and juvenile delta smelt is to maintain OMR flows somewhere between -1,250 cfs and -5,000 cfs until about June 30, or until the temperature at Clifton Court Forebay reaches 25°C. At least, that was the idea prior to Judge Wanger’s recent ruling in the Consolidated Delta Smelt cases.
The above equations are qualitatively consistent with the graphs, in that they depict the higher magnitude negative OMR flows induced by installation of the spring HORB. But they also remind us of the role that exports play in striking the right flow balance. In particular, the equations suggest that it should be possible both to install a spring HORB (to more fully protect salmon) while also minimizing negative OMR flows (to reduce entrainment of larval and juvenile delta smelt). The caveat is that forgoing the spring HORB makes it easier to achieve an acceptable OMR flow — at an export level higher than would be possible with the spring HORB in place. And therein lies the rub.
In other words, a physical HORB could be installed, and both salmon and delta smelt could receive fuller protection. The key, of course, is that someone has to make the policy decision to prioritize species over conveying water south of the Delta. It would also be helpful to avoid federal district court judges that have a penchant for granting injunctions against biological opinions. Contra Costa and South Delta diversions would have to be maintained within a reasonable range. But more importantly, it may be necessary to limit SWP and CVP exports to a quantity closer to 1,500 cfs, for a longer period of time than DWR and Reclamation would probably desire.