The Great Mexicali Energy and Shipping Canal
The Salton sea presently covers an area of 974 km2, at an elevation of 70 meters below sea level. An inflow of sea water sufficient to raise the lake level by one meter could generate some 200 gigawatt-hours of electricity. That's a gigawatt of continuous output for 8.3 days for each meter of lake surface rise -- enough to supply the seasonal difference in daily average for over 10 gigawatts of peak solar power.
An obvious issue is the distance from the Salton Sea to the Sea of Cortez (or the Gulf of California, as most of us know it). The image below, from Google Earth, shows the two. The Salton Sea is the dark body of water toward the lower left center; the view looks south toward Baja California and the Sea of Cortez. The distance is 185 km. That means the average elevation drop is a meager 38 cm. per km. After Harry's article, I commented that "It would need a diameter of at least 100 feet (for a pipe or tunnel) to move enough water over that distance to generate 10 gigawatts". That was the minimum scale I felt would be needed to justify such a megaproject. But even at that scale, the capital cost of such an enormous water tunnel would make the stored energy prohibitively expensive.
After mulling it over, I decided to do some serious figuring to see if there was any way the project could possibly be feasible. The conclusion I reached, surprisingly, is that in fact it could be -- if it's done right.
What does "done right" mean, and where was I wrong when I previously scoffed at the idea? It wasn't in my "guestimate" of a 100 foot diameter for a water tunnel. That was actually a little optimistic. To carry sea water for 185 km. with sufficient flow and head to generate 10 gigawatts at the end, a tunnel would need to be more like 50 meters in diameter! Even if it were technically feasible to build such a gigantic water tunnel -- which I rather doubt -- the cost would be orders of magnitude too high to pay off. So how do I conclude that the project could be feasible?
There are a number of considerations, but they start from the fact that the project does not require a tunnel! Instead, it would employ a large sea-level canal for 98% of the distance between the two bodies of water. The desert region above sea level that the canal would traverse consists almost entirely of young alluvial deposits from the Colorado River delta. The course is flat and barely 30 meters in elevation at its highest. Cutting a sea-level canal through that terrain would be a large but not otherwise challenging civil engineering project.
Using an open canal rather than a buried tunnel changes the mode of operation for the pumped energy storage system in ways that make it more efficient. I'll explain about that shortly. But more importantly, it enables the system to serve additional functions that enhance its economic and social value. In fact, energy storage might ultimately be among the least of its functions. The system would also serve for:
- large scale tidal power generation for northern Mexico;
Large-scale tidal power generation is enabled by the unusually large tidal swings at the northern end of the Gulf of California. The typical tidal variation at the Colorado River delta is around 7 meters, with two cycles daily.
Using the canal for shipping might raise a few eyebrows. One can question whether there is really a need for a canal to bring freight to inland ports in Mexicali and the Imperial Valley. But it has its points. It would bypass congestion and cut air pollution at the present port of Long Beach, while saving rail shippers the expensive climb out of the LA basin over Cajon and Beaumont passes. It would reduce the travel distance for ships coming through the Panama Canal to the U.S., and would lower the cost of shipping container cargo to and from the Mexicali region and the American Southwest.
As part of an energy project, the canal's use for shipping seems an afterthought. However, to adequately serve its "primary" energy functions, the canal must be BIG. So big, in fact, that it would be a waste not to use it for shipping. My rough figuring calls for 100 meters wide by 35 meters deep at its Gulf entrance. That is ample to allow two Panamax cargo ships, drawn by railed canal mules, to pass in opposite directions. And in economic terms, shipping would be far more than an "afterthought". The canal's shipping role could ultimately eclipse its energy functions. That's not so much from port revenues or the avoided costs of operations out of Long Beach, but rather indirectly. It would attract business and industry to the regions around the canal. Which brings us to the next point: infrastructure for economic development.
The broad desert areas surroundings of the canal route are prime locations for solar power. The energy storage capacity of the canal would provide the means to convert abundant but intermittent solar energy into reliable 24/7 grid power. Available land, clean reliable power, and easy access to worldwide shipping would make the canal a magnet for industrial development. That would bring jobs and residential development. But what about fresh water -- which is notably scarce in that region?
New supplies of fresh water for the region would have to come from desalination of sea water. Geothermal resources at the southern end of the Salton Sea could be useful for that purpose, but probably a portion of generated solar and tidal power would need to be tapped as well. Modern sea water desalination plants consume about 3.2 watt-hours per liter of fresh water output. (The theoretical minimum is .77 Whr / liter. 2) To meet the domestic water needs of a regional population of one million, some 200 million liters per day would be needed -- assuming no special efforts to reduce consumption below the 200-300 liters per day of the "typical" American lifestyle. If met entirely from desalination, that would be a steady 27 megawatts for desalination -- less that 1% of the average output from the solar installations that the canal could support.
We're now beginning to touch on the most controversial aspect of the project: its environmental impact. Before I can talk more about that, however, I need to backtrack and explain the physical characteristics of the canal. The features that allow it to serve for both energy storage and tidal power generation have a lot to do with its impact.
The main part of the proposed canal -- and 75% of the heavy engineering -- lies in Mexico. It consists of a large sea level canal that begins 20 km out in the Gulf of California, runs between sea walls to the shore, and then continues north-northwest for 130 km. to the U.S. border. From where it crosses the border, just east of the town of Mexicali, the canal route follows the sea level elevation contour almost due north for another 60 km. It meets the Union Pacific Railroad trunk line just east of the town of Niland, where it widens into an excavated harbor and seaport. The western shore of the sea level harbor will be only a few km. from the Salton Sea. Pipelines of manageable size complete the connection to the Salton pumping and generating station.
In addition to the canal itself, dozens of saltwater lakes and tidal marshes will be built along its course. Salt tolerant grasses and other plants will grow in the marshes, providing habitat for birds and fish. Although they have obvious environmental benefits, the lakes and marshes are functional components of the power generation and storage systems. They provide surface area to enable short-term storage of large volumes of sea water with minimal changes in water level.
The constructed lakes and marshes need not be deep; total surface area is what matters. Those near the south end of the canal provide storage for water delivered at high tide. Water is released from there at low tide for power generation. The rise and fall of water in these marshes mirrors the twice daily rise and fall of the Gulf of California tide, but at a reduced scale.
The lakes and marshes near the north end of the canal, in contrast, provide storage for water pumped up from the Salton Sea during hours of surplus power. The stored water is returned to generate power at night and other times when generation is down.
We can see now why the open canal works so much better in these applications than a water pipeline or tunnel. A pipeline is inflexible; it connects the two great reservoirs at either end, but to move any water between the reservoirs, it's necessary to move the entire 180 km. plug of water through the pipeline. That involves high losses to flow resistance. In contrast, the canal is is "elastic". It constitutes a long stretched out reservoir in its own right. There are seasonal average flows through it, drawing water from the Salton Sea in summer and replacing it with water from the Gulf in the winter. But the seasonal average flows are one to two orders of magnitude less than the daily flows that generate tidal power and supply load-following capacity to the power grid. With the canal system, those larger daily flows are mainly local -- between the primary reservoirs and nearby sections of the canal and its auxiliary lakes and marshes. Losses to flow resistance are drastically reduced.
Salton Sea Impact
There are several regions impacted by the project. The first is the Salton Sea itself and the area immediately around it.
From the 1930's and into the 1980's, the Salton Sea was a productive fishery and a popular destination for tourism and camping. But with no outlet, the waters have grown steadily saltier and more polluted from wastewater and agricultural runoff. Fish caught there are no longer judged safe to eat and can't be sold commercially. Algae blooms from high fertilizer levels in the water periodically deplete oxygen and suffocate fish. The stink from dead sea life has at times driven away tourists and campers.
Even more ominous for the Sea's future is that California has long been overdrawing its Colorado River allotment. Under court rulings, it is reducing its draw, which means less flow into the Salton Sea. Moreover, a larger portion of the fresh water that is drawn will be pumped to San Diego and other cities, rather than being used for irrigation in the Imperial Valley. With greatly reduced fresh water input, the Salton Sea will continue shrinking and becoming much saltier.
To address these issues, the regional county governments and water agencies got together in 1993 and formed the Salton Sea Authority. The Authority has studied a range of options for addressing the Sea's problems. Several of the early options studied involved canal and pipeline combinations for exchange of water between the Salton Sea and either the Pacific or the Gulf of California. Their focus was limited to stabilizing the water level and managing water quality in the Salton Sea, so they did not include the energy or shipping functions of this proposal.
In May 2007, the Salton Sea Authority issued its "Preferred Alternative and Funding Plan" 3. None of the canal and pipeline options made the cut for consideration in the final selection. That angered not just die-hard canal proponents, but also others who want to see the Salton Sea restored and maintained at its full current size. The "preferred alternative" that was selected reduces the marine sea to less than 10% of its present area. With no canals or pipelines for water exchange, the reduction is necessary in order to slash evaporation losses and accommodate the reduced inflow of irrigation runoff from the Colorado River.
I can't fault the Salton Sea Authority for the plan they selected. In fact, I think it's rather elegant, in the way it manages to preserve the existing shoreline while creating new wetland habitat. The Authority has selected what is probably the most cost-effective alternative for the specific problems it was chartered to address.
On the other hand, there's no question that the canal project described here would also serve to stabilize the Salton Sea and maintain its salinity at an ecologically productive level. The twice daily tidal flows through the canal combined with pumped storage operations would support a high volume of water exchange between the Salton Sea and the Gulf of California. It should be ample to avoid salt build-up, without the need for dikes and impoundments in the Salton Sea. The daily cycling of water through the salt marshes along the canal would provide natural filtration and fertilizer uptake that should eliminate problems with algae blooms. In terms of initial cost, it would be an expensive solution to the Salton Sea's problems. But it would be a solution.
The open water surfaces of the canal and its salt water lakes and marshes would be large enough to affect regional micro-climate. It would increase average humidity downwind of the canal by a small amount and moderate local day-night temperature swings. Since all moisture that evaporates at one location on the earth ultimately falls as rain somewhere else, the project should (theoretically) increase rainfall in northern Mexico, southern Arizona, and west Texas. Whether the effect would be large enough to notice, I don't know.
The real impact would be from the influx of business and population that would follow completion of the canal. The many dozens of storage lakes built around the canal would create some thousand miles of waterfront in what was previously empty desert. The bluffs formed by excavation of a large sea level canal would host prime view lots overlooking the landscaped canal corridor. It's likely that within two decades, the canal would develop into the central artery of an extended "linear city". That prospect will be sufficient to turn some environmentalists solidly against it. Many abhor the idea of building new cities in the desert, when the earth is already in crisis from overpopulation and dwindling resources.
I see it differently. We do face an urgent need to slash consumption and find ways to live more efficiently. However, when efficiency is the goal, building from scratch is often a lot easier than trying to reform a complex existing system. It's not actually all that hard to build super-insulated buildings that require negligible energy expenditure for heating and cooling -- even in the desert. It's also fairly easy to design for very low water usage. Dry climate landscaping, drip irrigation, and low-flush toilets are only the beginning. When fresh water must come from solar-powered desalination plants, there is an economic incentive to use it sparingly. Innovations like blown-mist shower systems, adapted from submarines, start to make sense. The planned communities that will develop along the canal route could be showcases for low-impact, post-carbon lifestyles.
The most problematic area of environmental impact would be to the Gulf of California. The Gulf is a rich area for marine biology. Its nutrient-rich waters are home to a range of unique species, and provide the winter breeding and nursery waters for the California Grey Whale. A sizeable region at its northern end is designated by the Mexican Government and by the U.N.'s Education, Scientific, and Cultural Organization (UNESCO) as a biosphere reserve.
The canal route that I described above would cut straight through the biological reserve. In itself, that wouldn't necessarily be a problem, because sea walls would isolate the canal from the shallow coastal waters and wetlands of the reserve. But construction of the canal and sea walls could be very disruptive. So an alternative route that would bypass the reserve might have to be used. That route would pass west of the Colorado River delta and open into the Gulf near the town of San Felipe, well south of the delta area. That route would be about 35% longer than the most direct route to the head of the Gulf. As it happens, though, there has long been interest in Mexico for building a sea-level canal along a good portion of that route. It would connect to and flood the dry lake bed of Laguna Salada, and create a local seaport for that region of Baja California.
The most controversial impact to the region is probably the large influx of tourists and recreational boating that the canal would enable. At present, the only access to the Gulf of California from the heavily populated California coast is a long slog around the Baja peninsula. That has kept the gulf comparatively unspoiled and free of large-scale development. The canal would most certainly change that. But that might not be a bad thing for local marine life. Isolation has by no means prevented the gulf's waters from being heavily overfished. Some once-popular species have already been fished to apparent extinction. A healthy tourist industry based around diving and sport fishing could be the only realistic way to curtail overfishing and conserve local marine life. At least, that seems to be how it has worked in some other areas.4
Notes and References 1. Valentine, Harry, The Potential for Seasonal Energy Storage, Click Here 2. Energy of Sea Water Desalination, Click Here 3. Click Here 4. See, for example Click Here and linked reports on the job creation and economic benefits of marine conservation. The jobs created are mostly in tourism, and provide relief to the poverty that drives overfishing in less developed areas.
1. Valentine, Harry, The Potential for Seasonal Energy Storage, Click Here
2. Energy of Sea Water Desalination, Click Here
3. Click Here
4. See, for example Click Here and linked reports on the job creation and economic benefits of marine conservation. The jobs created are mostly in tourism, and provide relief to the poverty that drives overfishing in less developed areas.