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Another look at the post-Panamax lock problem
 

Assessment of the locks for the Panama Canal expansion project

by Bert G. Shelton

The Panama Canal Authority, known by its acronym in Spanish as the ACP, has proposed using 19th century side-tank lock technology to improve a 20th century canal, which is most perplexing because the choice is both awkward and illogical. The fact that the side-tank system --- a system in existence for over a century --- is not widely used makes the declaration by the ACP that the system is the long-sought and “only” solution for the expansion of the Panama Canal a hard one to swallow. This article challenges that declaration.

Only one existing example of the side-tank system was presented during the system’s promotion, which is the one in Germany that was shown on the Discovery Channel. That example is relatively small and on a relatively quiet waterway, which makes it more of a curiosity than a system intended for heavy use. The presently proclaimed merits of the system do not fit with the fact that it is not in widespread use. A plausible reason for the system to leap from obscurity to stardom would be, for instance, that there has been a recent technological breakthrough that has improved the efficiency of the system. If there has been such a breakthrough, it hasn’t been brought to light.

The ACP has proposed using a side-tank lock set at each end of the Panama Canal. Each set would be comprised of three stair-stepped chambers in a single-lane and those chambers would each have three slave tanks, each as long and as wide as the lock chamber, and all located to one side. When operating the system, water flows by gravity to one slave tank at a time as the chamber’s water level is lowered and it flows back to the chambers from the slave tanks, one at a time, to raise the water level. That water represents 60 percent of what is used to move ships. Another 40 percent is either released when ending the lowering sequence or is added when ending the rising sequence.

The end result of the procedure is that the system requires only 40 percent of the water that is needed to operate an equally sized single-lane three-step “traditional” set of locks, but it takes time to do the required water-saving manipulations. The ACP has announced that their system is to perform 12 transits daily, which means there is an accumulation of time expenditures for handling the big ships, manipulating the water, and routinely reversing the lane, that will result in those relatively few transits per day.

In principle, the German example of the system operates in a way similar to what was described above. So, what improvement has occurred that now elevates the side-tank system to the top-ranked approach for lifting and lowering the world’s biggest ships and, also, that it merit being labeled the “only” viable alternative for improving the Panama Canal?

As no explanation has been offered and since no information of assessments performed by the ACP has been made available for unbiased review by others, there is concern that this heavily-marketed, in-house proposal has not been rigorously assessed and rests on neither sound technical nor financial, footings.

The purpose of this article is to present another lock system that is not only a viable alternative to the side-tank system, but a superior one. This article identifies other key elements or choices that accompany the selection of the locks that need further assessment and comparison to confirm them.

Only hydraulic ship-lifts, known as locks, will be addressed in this article because the ACP considers mechanical ship-lifts “too risky” for their canal. Many engineers take exception to that position, but this article will remain focused on locks. 

Superior 20th Century lock technology of the existing Panama Canal

Locks designed using the Panama Canal’s own lock technology can out-perform the side-tank locks proposed by the ACP to improve the canal, as was suggested by the opening statement of this report. That fact can be proven using the canal’s own single-step two-lane locks at Pedro Miguel.

A single-step two-lane lock similar to the lock at Pedro Miguel can be operated in a highly efficient way with regard to water use. When a ship exits a chamber of that style of lock, another ship going the other way can take its place, which means one chamber-full of water provides for two transits. Combining that mode of operation with the lateral water transfer capability existing in all of today’s Panama Canal Locks --- a lateral water transfer method similar to that of a side-tank system --- four transits can be completed with the amount of water typically used for one.

Two-lane locks, transiting ships in both directions in this fashion, will use 25 percent of the water per transit that a traditional single-lane locks with chambers of equivalent size operating in one direction would use per transit. And, that is a lot better than the 40 percent water-use figure publicized for the ACP’s triple-side-tank system.

In order to take advantage of the Pedro Miguel style lock’s water-saving potential, there have to be three separated single-step two-lane lock structures installed, rather than building all three steps together in one structure. Therefore, there are operational issues to be assessed prior to making final choices, which will be discussed later in this article.

There is more. The 25 percent water-use of a Pedro Miguel style lock includes lane reversal, whereas the 40 percent for operating the ACP’s three-step single-lane side-tank lock is without lane reversal. So, Pedro Miguel style locks operated in their highest efficiency mode actually save somewhat more water in comparison.

When a three-step single-lane lock is reversed a full cycle, from lifting ships to lowering them and back to lifting again, unavoidably two transits-worth of water must be released that move no ships. If one considers that at least one full cycle reversal will be done each day for the 12 transits the ACP announced for their system, those 12 transits of their three-step single-lane lock will use 14 transits worth of water. Taking into account the two extra loads of water that must be used to operate the side-tank system, the real water-use figure increases from 40 percent to 46.7 percent. That latter figure is the more accurate to use when comparing the ACP locks to the Pedro Miguel style locks of equal chamber size.

What this means is that both lanes of a Pedro Miguel style lock can be operated at the same time using just a little more water than is used to operate the ACP’s single-lane triple-side-tank lock. Among other benefits, this means there is capacity for many more transits.

And, that is not all. There is serious concern that Gatun Lake will become brackish because the side-tank locks will bring more saltwater volumes to the level of the lake with greater salt concentrations compared to what the existing locks bring in their routine operation. By contrast, operation of a lock system, based on the locks at Pedro Miguel, reduces the salt intrusion problem significantly in two ways.

Firstly, the mode of operation that brings in the most salt, which is to exit several ships in a row, is eliminated. With the Pedro Miguel style lock being reversed ship-by-ship, there will always be a ship in the chamber that is to be filled. Therefore, that chamber will contain the least amount of saltier water to be diluted by the water used to fill the chamber because the ship’s volume will have displaced a significant amount of saltwater from the chamber. With less saltwater to dilute, the resulting mixture will have a lower salt concentration.

Secondly, there is better dilution of the seawater involved. This is because 25 percent more water is involved in the dilution process with the Pedro Miguel style lock as compared to the water involved in operating triple-side-tank locks, which is due to ship-by-ship lane reversals.

In the final analysis, the Pedro Miguel style locks offer a significant improvement over the ACP’s proposed triple-side-tank system, whether they completely solve the salt intrusion problem, or not.

The bottom line is that if three separated two-lane single-step Pedro Miguel style locks are used at each end of the canal, water will be more effectively used --- with more ship transits per day --- and the lake will be better protected.

Phased construction and operation of Pedro Miguel style locks

A financial benefit to building Pedro Miguel style locks is that their design provides the Panama Canal Expansion Project with the option of phased construction and operation of the locks, which the ACP-proposed triple-side-tank locks do not. One of the two lanes can be built and brought into operation before the second lane is complete.

Operating the first lane alone once it is complete would use 50 percent instead of the 25 percent of water per transit that will be used once both lanes are ready. That 50 percent can be compared to the more accurate figure (taking lane reversals into account) for the triple-side-tank locks of 46.67 percent of water used per transit, as noted previously.

In terms of transits, operating the one lane would permit 11 per day as compared to the 12 per day projected for the proposed triple-side-tank locks. However, those 11 transits per day would help finance completion of the second phase, which would be the follow-on construction of the second lane.

Once both lanes are in operation, the Pedro Miguel style locks benefits become clearer. With both lanes ready, transits would double to 22, without a need for more water, and there would be the fallback of having another lane available for when one is closed for maintenance, which is not available with the ACP’s design.

Additional elements to evaluate

Several elements of the Panama Canal Expansion Project (besides the locks themselves, but intimately linked to the choice) are unclear in the ACP’s plan. The plan as presented prior to the national referendum lacked a proper Design Basis to orient a reviewer and did not include a development history for individual elements, so uncertainty persists as to how particular elements were defined.

For instance, how chamber size was set is unclear just as the issues which led to choosing the current three-side-tanks-per-chamber design, or its two-side-tanks-per-chamber predecessor for that matter, remain unclear.

How it was decided to change the fluctuation range of Gatun Lake, instead of choosing another water-storage improvement approach for the existing watershed from the many approaches that have been proposed in the past, was not clarified either.

In the sections that follow, other plan elements such as those listed above will be described and discussed, and recommendations given where appropriate.

Increasing new lock chamber size to more effectively operate the locks

Water is most efficiently used to transit cargo when a lock chamber is filled as much as possible. The most efficiently transited ships through the Panama Canal are the Panamax ships, because they most completely fill the chamber. The block of water that is added below a Panamax ship to lift it, or drained from below to lower it, moves the most cargo tonnage possible. Cargo efficiency for all ships smaller than Panamax is less because the block of water must be added or discharged is the same, but the cargo moved is less.

The desire now is to transit ships larger than Panamax. Logic suggests that, for times when none of those larger ships are seeking transit, dimensions of the new lock chambers should be such that several ships --- of the size most typically transiting the Panama Canal --- can fit into the new lock so as to fill it more completely more often.

The ACP has defined a lock chamber --- 1400 feet long by 180 feet wide and 60 feet deep --- as the optimum size for future needs; however, those chamber dimensions do not allow multiple ships of the size typically frequenting the canal to share a transit. That results in significant under-utilization of their system when there aren’t ships larger than Panamax to be transited.

The ACP has explained that this size was defined as the result of extensive discussions with port authorities and clients in the shipping business from around the world, but their reasoning is unclear and the actual criteria the ACP used to come up with the dimensions they proposed are unknown.

Maximizing the yield of current water resources by using them more efficiency should be the goal, rather than promoting the inefficient use of more resources.

To efficiently use water, chamber size should be optimized to allow the maximum number of transits with the water that is currently available. A chamber long enough and wide enough to fit four ships of the size most frequently transiting the canal should be considered.

With such a chamber size, already in phase one (operating only one lane) the proposed Pedro Miguel style locks would transit four typical ships using one-half the water that is used in today’s locks to transit each of them. This important efficiency gain makes “borrowing” water from the existing locks a viable method for maximizing the overall performance of the Panama Canal and makes Pedro Miguel style locks viable and superior for the canal’s expansion.

As an example, assume a Pedro Miguel style single-lane lock, fitting four “smaller” ships, were operated 11 times per day. It would transit 44 of the “smaller” ships using the water that today transits 22 of them. The existing locks transit 38 ships on an average day, so with 22 transits-worth of water “borrowed” for the 11 transits of the new locks, there would still be 16 transits-worth of water left to operate the existing locks each day. The existing locks, which have the capability of being operated with half the water traditionally used, could then transit 32 ships with the remaining water that typically transits 16.

Combining the 11 operations of only one lane of the new locks, transiting 44 ships, with 32 ship-transits through the existing locks yields a per-day transit-total of 76 ships. That total is double the ships that transit the present canal. When the second lane begins operating, the total increases by another 44 for a grand total of 120 transits. This is triple the ships that transit today’s canal, but without any increase in the water used.

If chambers are sized as recommended, Pedro Miguel style locks could accommodate larger ships (with more cargo tonnage) than those envisioned by the ACP in their proposal and could also provide for better maneuvering of the typical “bigger” ships into the chamber. Easier to handle “smaller” ships could be put into the chamber after the big ones have entered to further maximize transit tonnage.

The ACP’s plan is to handle ships using tugs instead of the rail-mounted “mules” that run atop the walls of the existing Panama Canal Locks, and canal equipment operators have voiced understandable concerns with that plan. Developing ways to handle big ships and groups of ships effectively and efficiently in and out of locks is needed regardless of what alternative is built.

The Panama Canal’s limitations no longer arise from water resource availability, but rather from the challenge of handling larger ships and greatly increased transit volumes through the locks, the channels, and across the lake itself. This important shift has enormous repercussions on the environment surrounding the canal.

Maintaining existing lake level variations

The previous discussion on optimizing the lock chamber size concludes that there is no need to change the way Gatun Lake is managed today.

The complex and costly need to alter the lake’s water level fluctuation range can be eliminated. With the right lock selection and sizing, the existing lake --- as is --- can provide for 200 percent more “typical” daily ship transits or for up to 22 “bigger” ships a day with smaller ships accompanying them, depending on space available in the chamber.

Nonetheless, a variety of options to increase the water reserves of the current canal watershed, such as damming one or more of the rivers within it above Gatun Lake have been contemplated in the past for bridging unusually long dry-seasons, and that still needs to be attended.

Nearly 50 percent of the water falling onto the canal’s watershed goes to the sea unused, and retaining some more of that would be the prudent thing to do. Several rivers to possibly dam have been identified by past canal administrations, as well as has the option of going outside the current watershed and claiming other water resources.

Optimizing the use of water

An important principle to remember throughout these discussions is that there is a cost in time to save water, and time is money. It is inefficient to build a system that saves water but runs out of hours in a day to transit all the ships that could be transited with the available water supply. Likewise, it is inefficient to build a system that uses more water and transits ships more quickly, but runs out of water before the day is out. A balance must be struck. 

The ACP chose a lock arrangement with three steps probably because structural limitations make it impractical to reduce the number of steps, and also because reducing steps requires more water of which there wouldn’t be enough of anyway, even if structural limitations weren’t an issue.

In the other direction, increasing the number of lock steps reduces the amount of water needed to operate the system, but it increases the construction costs and subsequent lock operations. For single-lane systems, more steps would also increase lane reversal time.

The guess is that in looking for a quick and economical solution to find an adequate balance, the ACP resorted to the side-tank system figuring that they could inexpensively solve the water-shortage problem by adding a couple side-tanks to a single-lane lock set to cut water-use in half. That might have been good enough and they would likely have been done, if they had not run into a snag. 

The ACP was originally going to get the additional water needed by expanding the canal watershed to the northwest, but that got politically axed due to a public outcry over how doing so ignored the needs of the areas population and that it was an ill-conceived and unfair decision. So to compensate for the political “loss” of that water, the ACP went about modifying the system they had hand-picked rather than evaluating other alternatives. It appears they have worked themselves into a proverbial hole.

They added a third side-tank, one that only reduces water-use another 10 percent, and declared that the system would work by increasing the variation of the lake level, and doggedly pushed that plan through a required national referendum.

Not only is adding the third side-tank inefficient with respect to cost versus gain obtained, the consequences to side-tank lock water-management resulting from the proposed lake-level fluctuation change have seemingly been ignored. Also, the impact the water-level change will have on facilities all around the lake has been downplayed. And, nothing has been said about transit time and how the addition will impact that.

Panama Canal Expansion Plan challenges

In order to explain the challenges that current Panama Canal Expansion Plan appears to be confronting, it is first necessary to expand on how side-tank systems work.

As the number of side tanks is increased, the water-savings grow at a decreasing rate; the water-savings added by another side-tank is markedly less than that of the one that preceded it. If a lock is designed with one side-tank beside each chamber, water consumption can be reduced to 66.67 percent; two side-tanks drop water consumption to 50 percent; three side-tanks drop water consumption to 40 percent; four side-tanks would drop it to 33.33 percent; and six side-tanks are needed to drop water-use to 25 percent. In other words, one side-tank reduces the water needed to perform a lift by 1/3, but it takes four to reduce it by 2/3 and six to reduce it by 3/4. Clearly, hardware requirements (tanks, pipes, valves, etc.) can get out of hand quickly when trying to save more water using side-tanks.

What is more, side-tanks become ineffective quickly with respect to operating time, as well, because having to drain the tanks in sequence grows increasingly slower as the average water pressure for draining the tanks is progressively reduced. Water is saved, but the number of transits that can be achieved in a set amount of time ends up suffering; and, time is money.

The old-timers who designed the exiting canal figured that out long ago, which is why the side-tank lock in Germany was of limited interest to them.

As was noted earlier, the ACP apparently opted for a two-side-tank per chamber lock arrangement initially because they knew they only had about enough water to operate a one-lane lock at 50 percent water-use per transit. For them, a two-lane lock system that cross-locked water to obtain 50 percent water-use was not an option because, with the water available, a two-lane system would have ended up idle half of the time.

By combining cross-locking with lane reversal at each step --- also figured out long ago by the old-timers --- water-use would be reduced to 25 percent, and by phasing construction of the second lane to help manage financing, a two-lane system could have been justified with the available water. As the ACP has not shared information regards the options they evaluated, it is not known whether or not they were aware of the combined approach, or if they discarded it after an evaluation, or if they simply opted to ignore it.

To maximize water savings with the Pedro Miguel style lock approach, ships must be captured and released at each lock step. It is well known that the ACP and ship owners dislike immensely having to do that today at Pedro Miguel, mostly because that operation increases the ship residence time in canal waters and typically comes with no benefit. But, it is being done about 38 times a day and ships keep coming despite that “inconvenience.”

With this recommended combined approach, by contrast, there is a benefit. Water-use is cut in half by that extra time, which is what has to happen to save water. It must not be forgotten that the ACP’s chosen system also takes time to save water, but doesn’t save nearly as much water.

With locks in the Pedro Miguel style, ship transits can be completed in about the same amount of time it takes to transit a triple-side-tank lock; but the water-savings obtained is that of a six-side-tank lock.

The reason for this has two parts. The greater water-savings of a Pedro Miguel style lock are obtained with half the water manipulations of a triple-side-tank lock. Water movements happen in less time because the average water-pressure is higher. Adding an appropriate share of the lane reversal time of a three-step, triple-side-tank lock to the difference in water manipulation time between lock systems being compared, results in comparable total transit times for the two systems; but with the Pedro Miguel style system offering the superior water-savings.

And, that is why side-tank locks were forgotten and left behind long ago.

Concluding remarks

To put all that has been addressed here into perspective, consider that it would take two lanes of side-tank locks having six side-tanks per chamber to obtain the water-savings of a two-lane Pedro-Miguel style set of locks. And, that side-tank lock system would still not yield the same ship throughput because there are not enough hours in a day.

The shortage of water is not the main issue of concern in enlarging the Panama Canal. The key issue lies with ship handling, which includes the managing of many more ships through the canal, as well as the transiting of the locks.

With respect to the locks, developing the procedures and equipment to streamline the ingress and egress of big ships or of multiple smaller ships into and out of chambers is where the work lies. Many ideas spring to mind, but discussing them now is outside the scope of this article.

For the purpose of expanding it, the Panama Canal’s “water shortage problem” can be solved by simply using the technology available in its existing locks to the fullest, designing a superior alternative to the side-tank system. However, present day dry-season water shortages still need to be addressed.

Using Pedro Miguel style locks for enlarging the Panama Canal eliminates the situation that causes the most salt intrusion. Changing the lock selection from the side-tank system to Pedro Miguel style locks can be justified on this point alone.

The advantages of considering a change of lock design are not only limited to those described above.

With fewer water manipulations, the Pedro Miguel style locks will be simpler in layout and easier to operate and maintain. Separated lock steps allow Miraflores Lake to be included in the new system and the need to dig an over 3-mile-long virgin channel to bypass the lake is avoided, which saves a lot of work. Also, better advantage can be taken of the US Army Corps of Engineer’s past excavation efforts. By not altering the lake, significant savings from less dredging and from not modifying existing installations result, as well. Nonetheless, the task of digging and dredging will still be monumental.

In the final analysis and with all issues diligently assessed, the expectation is that expanding the canal using a Pedro Miguel style lock will result in project costs not greatly different from what is currently planned, yet with significantly greater returns obtainable from the system and significantly less environmental impact.

The author is an engineer and a research scientist

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