Another biological problem with the Twin-Tunnels’ intakes:  Like gigantic vacuum cleaners, the flow pulled through the river intakes will likely suck baby salmon up against the fish screens (called “impingement”).  To minimize this problem, low through-screen water velocities (also called approach velocities) are necessary to hopefully prevent young salmon from encountering physical, injurious contact with fish screens.  The WaterFix proponents “promise” to keep those velocities low.  The biological problem with this premise is that juvenile salmon are weak swimmers on a sustained basis and cannot tolerate swimming against approach velocities through the screens for long periods.  When naturally migrating downstream, the small fish essentially “go with the flow” and do not aggressively fight against the current, except in unavoidable desperation (see: Struggling Salmon).  To avoid impingement, the salmon suddenly have to fight against the flow entering the WaterFix intakes.  The small salmon can only combat the currents for short periods until fatigue sets in and eventually succumb to the water flowing into the screens.

In the not-so-distant past, to minimize this fish impingement problem, a federal criterion mandated that young salmon should not be exposed to fish screens for more than 60 seconds, even with low approach velocities.  The biological concept is to move salmon very quickly past the screens before the fish surrender to the through-screen velocities, come into contact with the screens, and eventually die from abrasions and physical injury.  With large, long screens, this poses a very serious predicament.  In case of the Twin-Tunnels’ screens, it will not be possible to get the salmon away from the screens in less than a minute because of the large surface area and great length necessary to keep the through-screen velocities low while simultaneously maintaining high water diversion rates.  The salmon can only escape if swept by the long screens extremely fast.  In this regard, the Twin-Tunnels’ fish screens will perform miserably.  Because of the poor locations of the intakes discussed in the first of this series, salmon will be exposed to the proposed screens for long periods because of severely low sweeping flows.  Analyses conducted for the project revealed that young salmon could be exposed to each of the three individual WaterFix screens for an astounding one-hour period (not a typo) … not exactly the original 60 seconds criterion mentioned above.

Additionally, it will not be possible to maintain uniform through-screen velocities along the entire length for each of the three screens.  Therefore, WaterFix proposes to install “flow-control baffles” directly behind the screens.  These would typify tall vertical Venetian blinds (Figure 1).  The WaterFix idea is that if too much flow (and therefore unacceptably high through-screen water velocities) occurs in a particular area (“hot spots”), the baffles would be pinched down to restrict flow entering that particular area of the screens.  The problem, in reality, is this proposed engineering solution will be like chasing ghosts.  As river flows and diversions change dramatically, the through-screen velocities and complex secondary currents will also change significantly over the entire area of the fish screens.  Tweak the baffles upstream, then it’s time to adjust the baffles downstream, and so on.  Once done, everything changes hydraulically and you have to start all over again … a never-ending battle of futile attempts to achieve the fairytale of flow uniformity over the entire screen face under all river and water diversion conditions.  Whew!  I would not want to be the poor workers chasing back and forth over the combined ¾ of a mile of fish screens constantly tweaking baffles 24 hours a day, 7 days a week when water is being diverted into the Twin Tunnels.

Figure 1. Picture of flow-control baffles in the open position (foreground) and flat-plate screens in the background. Entire structure dewatered during construction. Picture by Dave Vogel.

Unlike agricultural diversions in upstream areas that primarily divert water during the spring, summer, and fall, the Twin-Tunnels’ intakes will be diverting water over the winter season under high-flow conditions.  Unfortunately, this will undoubtedly cause unavoidable massive debris loading on the screens.  In attempts to deal with the plugged screen openings caused by debris, enormous vertical “wiper blades” will be in continuous operation going back and forth against the screen surfaces.  Envision giant tooth brushes constantly scrubbing in a futile attempt to stop the persistent “plaque” build-up (Figure 2).  Some existing smaller flat-plate screens used in upstream areas (where debris loading is far less and sweeping flows are very high) have successfully employed such wiper blades, but those situations are far different than envisioned with the proposed Twin-Tunnels’ intakes during the winter.  The Twin-Tunnels’ unfortunate reality is that with the poor sweeping flows, it will be extremely difficult, if not impossible, to get rid of the debris.  And where will it go?  The detritus will merely drift downstream and continue to plug the next screen panel, then the next, etc., etc.  The increased debris loading during high river flows is likely to be enormous¹, overwhelming the wiper blades … WaterFix has not adequately addressed this dilemma.  And … for those hapless, fatigued young salmon struggling against or impinged on the screens when the robotic wiper blades bear down on the fish under the cover of darkness and muddy water? … Squish.

Figure 2. Picture of a flat-plate screen wiper blade. Entire structure dewatered during construction. Picture by Dave Vogel.

Next in the series:  The myth of the Twin-Tunnels’ salmon “motels”.

The proposed “Twin-Tunnels Project” (aka “WaterFix”) would divert enormous quantities of water¹ from the Sacramento River to the south Delta for export into the San Joaquin River basin and southern California. If the project is built as presently planned, it will likely be a disaster for salmon for reasons described in this series. Water entering the two gargantuan tunnels would be pulled through three colossal water intakes² directly on the banks of the Sacramento River, a short distance downstream from the City of Sacramento. Except when the Yolo Bypass is flooding, all four runs³ of Chinook salmon in the entire watershed would be forced to migrate past these enormous diversions. Three extremely long flat-plate fish screens would be positioned in front of each huge water diversion intake (Figure 1). The size of these screen structures will be massive, greatly exceeding the size of existing fish protective facilities in California. The combined length of the three screens will extend nearly 3/4^th of a mile! The concept has never been tested elsewhere, possess numerous harmful obstacles for fish, and will likely kill large numbers of salmon. There is a high probability the structures will be catastrophic for salmon and severely undermine progress for salmon restoration in upstream areas. This series provides some highlights into the scientific basis to support that premise.

Figure 1. Conceptual rendering of one of the three on-bank intake facilities on the Sacramento River for the Twin-Tunnels project (Figure 3-19a from the 2016 Final EIR/EIS).

Location, Location, Location

Just like the old adage with real estate, fish screens must be located in good locations. Based on my 35+ years experience in the evaluation and bio-engineering of fish screens, in terms of hydraulic, physical, and biological conditions for fish protection, the proposed water intakes for the Twin-Tunnels are sited in some of the worst locations. Over a period of years, the Twin-Tunnels proponents presented the state and federal fish agencies with multiple hypothetical intake locations. It is evident that the agency representatives had no choice but to play with the losing hand dealt to them and recommended only general criteria that were severely constrained by the intakes sites. All of the options put forth were crappy … really crappy… for fish protection. It is obvious to me that the sites ultimately designated for the Twin-Tunnels project were not chosen because those locations would provide good fish protection but, instead, viewed as more favorable (but still bad) among the worst locations made available.

Because of the bad locations, the Twin-Tunnels’ screens will not have good “sweeping” flows to get the salmon out of the danger zone at the screens. Modern-day fish screens possess several features to help overcome the sweeping flow predicament for the Twin-Tunnels project. Sweeping flow complications can be partially alleviated by locating the screens on the outside bends of the river channel. An existing example of large Sacramento River flat-plate screen location demonstrates how that measure has been successfully implemented (Figure 2).

Figure 2. Aerial photograph showing an existing Sacramento River flat-plate fish screen located on an outside river bend to maintain high sweeping velocities. Water velocities passing the screen typically range between 2 to 4 feet/second.

In sharp contrast to such a real-world example, the three WaterFix intakes would be positioned in only very slight (or “gentle”⁴) river bends or relatively straight sections of the river channel (e.g. Figure 3) and, in all cases, undesirable lower gradient reaches of the river. Additionally, the Twin-Tunnels diversion intakes will be located in areas subject to tidal influence, further exacerbating the problems of ensuring protective sweeping flows. When the tide comes in twice a day, sweeping flows are reduced to the detriment of salmon.

Figure 3. Aerial photograph showing the approximate location of the proposed WaterFix downstream-most intake (termed “North Delta Intake No. 5”).

In summary, the Twin-Tunnels’ diversion sites will not provide the near-screen sweeping velocities necessary to protect downstream-migrating salmon. The noteworthy point is that past experience has clearly demonstrated that maintaining high sweeping velocities in front of large riverine flat-plate fish screens requires at least one of following to take place:

1. Alter river channel geometry and create channel constrictions to control the hydraulic conditions at the fish screens.
2. Position the fish screens on the outside sharp (not “gentle”) bend of the river channel where high water velocities are naturally present (e.g., Figure 2).
3. Angle the fish screen out into the river channel in a downstream direction or jut the entire structure out into the channel in deeper, swifter water to maintain sweeping flows.

Unfortunately, the Twin-Tunnels’ intakes do not possess any of those conditions — period. Even the recently-issued National Marine Fisheries Service’s Biological Opinion on the Twin-Tunnels Project admitted that there is “a high degree of uncertainty” if the fish screens can be built to meet fish protection criteria because of the immense nature of the proposed screens.

Next in the series: How to squish baby salmon on a fish screen.