Cruising to Vegas: Carbon and Climate Change
- June 13, 2016
- 162 views
Last week, I wrote about “The Treasure of the Sierra Nevada” — the treasure being trillions of tons of soluble carbonate minerals salted away in and below the desert playas of the Great Basin. The minerals are the stranded byproducts of several million years of chemical weathering of granite and other rock on the eastern slope of the Sierra Nevada mountains. The weathering products never made it to the sea, because the runoff waters that carried them flowed into the Great Basin and evaporated.
Here’s the deal: if we could somehow arrange for these weathering products to complete their aborted journey to the sea, then natural conversion of soluble carbonates to bicarbonates in the ocean would add enough alkalinity for the ocean to easily soak up all the fossil carbon we’ve dumped into the atmosphere since the dawn of the industrial era.
Of course we couldn’t possibly transport all of that deposited material to the ocean. Among other things, it would require turning half the state of Nevada into a giant open-pit mine thousands of feet deep. And even if we cared nothing about Nevada, we wouldn’t want to transport more than a fraction of the accumulated deposits. There’s so much there that we’d not merely be returning atmospheric CO2 to pre-industrial norms; we’d be lowering it enough to start a new ice age.
However, though excavating and transporting trillions of tons of weathering products is neither feasible nor desirable, a “mere” gigaton or so per year is another matter. It might be feasible, environmentally beneficial, and even (gasp) profitable. How, you ask? Read on!
Most efficient transportation
The most energy-efficient form of transportation is and always has been by water. On the oceans and the Great Lakes, the extreme low energy cost per ton-mile of cargo that giant tankers and cargo ships deliver is well known. But even inland, the most energy-efficient option for transporting bulk cargo is barging on navigable rivers and canals. Before the advent of mechanized railroads in the 19th century, nearly all heavy commerce moved by water. Factories and industry grew along waterways. Even today in the US, the Mississippi River and its navigable tributaries are important arteries for moving bulk cargo.
Of course, inland water transportation is far from speedy. Under way, a modern tow of barges on the Mississippi might make 5 knots. So barging is generally limited to bulk cargos that don’t need to arrive in a hurry. But bulk shipments of carbonate minerals from the Great Basin would certainly qualify on that score — if there were a canal on which to ship them. There isn’t, but might it be possible (and economically feasible) to build one?
If you asked an experienced civil engineer that question, there’s a 90% chance that the response would be “Are you out of your friggin’ mind?” Possibly more polite, but that would be the gist.
The problem isn’t so much the channel excavation and lining; that wouldn’t be very much harder than building a new 4-lane interstate through rural countryside. The cost of the latter varies widely depending on terrain, but per a 1996 History of Transportation article by William Grossman for Collier’s Encyclopedia, the cost is usually a bit over $1 million per mile. For a project of the sort we’re talking about here, a cost even five times higher than that would not be a show stopper.
For a “Pacific and Great Basin Canal” of conventional design, the larger problems are twofold. One is the number and size of the locks that would be needed. The other is the water flow that would be needed to operate the locks. Or rather the lack of it.
Conventional locks are a Big Deal. Barge canals are generally regarded as practical only in flattish terrain where there is minimal need for locks. There must also be an adequate water flow through the canal to operate such locks as are needed. Routes from the Great Basin to the Pacific don’t qualify on either score.
The playa regions of the Great Basin where carbonate mineral deposits are most accessible are at 4000 feet or more above sea level. The lowest pass into those regions across the hills north of Las Vegas is a little over 5000 feet. So the canal would need to traverse some 6,000 feet of elevation change. By comparison, the elevation change through the Panama canal is only 170 feet: 85 up and 85 down. Two flights of three locks in each direction are employed to accomplish that. The largest rise is 31 feet. The locks are massive structures; their construction was a major feat of the engineering in 1914 when the canal was completed. Yet here I propose a canal with 35 times the elevation change in a desert where there’s essentially no water flow? Ridiculous!
But hold on, please. Yes, it would be ridiculous if I were talking about a canal with dimensions that could accommodate Panamax freighters and massive locks like those built for the Panama Canal. I’m not though. River and canal barges are typically only a fraction of the beam and draft of a Panamax freighter. They’re nonetheless capable of hauling heavy tonnage economically; just not as much in one go. Also, there are alternatives to traditional locks that are much more efficient. They don’t require a flow of water.
Indeed, the aridity of the Great Basin and desert regions through which the canal would pass is one of the better arguments for building it. As a “free” side effect, the canal would bring high volumes of water to the area. Granted, it would be seawater, not usable for regular crop irrigation. But it would support an extensive system of saltwater lakes and marshes along its route. Much of the water transpired by marsh plants and evaporated from the lakes in the desert environment would return as sorely needed rain and snowfall in the Colorado River watershed. As a collateral benefit, the canal turns out to be a worthwhile fresh water supply project for the parched Colorado River basin.
Lifts, not locks
The first photo below shows a flight of traditional locks built for passing canal boats up and down a substantial hill — Caen hill in Wiltshire, England to be precise. The flight, a section of the Kennet and Avon Canal, employs 29 locks rising 237 feet in 2 miles, according to its Wikipedia writeup. Note the sequence of ponds ascending the hill on the right side of the image. They’re extensions of the pounds, the level sections of water impounded behind lock gates. Normally the pounds are just long level sections of the canal between locks. For the Caen hill ascent, however, the regular pounds between locks are very short, They don’t have enough area to quickly fill the next lock down the flight, or receive a flood of water from the gate above, without an unacceptable change in water level. Hence the pound extensions to the side. The arrangement allows the locks to fill and empty many times faster that the natural flow of water in the canal would allow.
Despite the clever pound extensions, it still takes about twelve minutes for a boat to cycle through each lock. Most of that is the time it takes for enough water to flow into or out of the lock chamber to raise or lower its level by the roughly 8 foot increment between each successive pound.
A more efficient alternative to this traditional type of lock system is termed a boat lift. A beautiful example is seen in the Falkirk Wheel, pictured below, near Edinburgh Scotland. It raises and lowers canal boats 24 meters in one step to link two separate canal systems.
The Falkirk wheel isn’t the most cost-effective design for a boat lift. The heavy cantilevered loads on those elegant rotating arms are very demanding. However minimizing cost wasn’t the top priority for its designers. The lift was intended, in part, as an architectural monument for Britain’s Millennium Link project. The emphasis on elegant appearance notwithstanding, it is remains impressively efficient. The balanced gondolas at opposing sides of the wheel each carry 500 tonnes of water and canal boats. Each 180-degree cycle of load / rotate / and unload takes about 15 minutes — mostly for loading and unloading. According to this Wikipedia article, the old set of 11 locks for which the wheel was a replacement required most of a day for boats to get through. By a supremely British metric, the energy needed to cycle the wheel through one turn is reckoned as equivalent to what it takes to brew 8 kettles of tea.
The reason behind the efficiency and speed of a boat lift is that energy is not being dissipated by pouring water into or flushing it from a lock chamber to raise or lower the boats within. Instead, what amounts to a moveable section of the canal itself is mechanically raised or lowered to allow boats in that section to move between two levels of the canal. The moveable lift sections are usually paired, with the rise of one balanced by the descent of the other.
Thanks to Archimedes principle — that any object that floats in water will displace a volume of water whose weight is exactly equal to the weight of the object itself — the weight of the lift sections does not depend on the size or number of boats floating within it. The weight only depends of the water level within the section. If the water levels are closely regulated, the weights of the ascending and descending sections balance. So while the immediate forces and the mechanical power required for raising one of the lift sections can be very large, both are supplied by balance with the descending section. The paired lift sections operate as a kind of see-saw, with the net power limited to what’s needed to overcome friction.
The Falkirk wheel serves a canal that cuts directly across the contour lines of a hill. That’s appropriate when a steep rise separates two runs of the canal across relatively level terrain on either side. But it means running a section of the canal as an aqueduct traversing the rise. The extension bringing the upper canal to the Falkirk Wheel is scenic, but was challenging to build. And the larger the canal and higher the rise, the more challenging the aqueduct becomes.
In hilly terrain of the type that the Great Basin canal would traverse in places, the canal route would not cut across contour lines. It would follow one contour for some distance (with strategic cuts and fills to straighten the curves), and then hop to the next. The “hops” would be at boat lifts running directly up the slope between the two contours. A small example of such a lift is pictured below.
Now we’re coming to the interesting part for clean energy fans. The proposed Great Basin canal would not merely be a system for transporting heavy loads of soluble carbonate minerals from the Great Basin to the Pacific. It would be an important resource for clean power generation!
There are two main aspects of the canal as a clean energy resource. One is direct hydroelectric power generation. The other is pumped hydroelectric storage. We’ll look at power generation capability first. It’s non-obvious and requires some explanation.
The capability derives from the fact that the overwhelmingly dominant flow of cargo in the canal is from clay and mineral deposits at 4000 feet above sea level, transported down to sea level. Every ton of material loaded onto a canal barge at 4000 feet will displace a ton of canal seawater. As the barge moves down the canal toward the Pacific, it shifts a corresponding mass of seawater up the canal.
Assuming we want to leave saltwater lakes and marshes behind where we’ve excavated the carbonate materials, about 40% of the seawater shifted up-canal will be needed to fill the volume vacated when the materials were removed. The rest is potentially available to be sent back down the canal. On its 4000 foot descent, each metric tonne of seawater generates (and/or dissipates) 3.35 kilowatt-hours of energy. We’re shooting for a transport rate of one gigaton of minerals per year. 60% of that would be 600 megatons of seawater, for some 2 billion kilowatt-hours of energy per year. That’s a 24/7 average power of about 230 megawatts.
The actual power available to the the grid would be considerably less. Hydroelectric power generation is only about 89% efficient, and much of the power generated would be needed to move the barges and operate the boat lifts. However the biggest loss is that the flow available for power generation would likely be much less than 60% of the flow of minerals. That’s because a good portion of the seawater shifted up-canal by the down-canal movement of loaded barges would be needed to cover evaporation losses from the canal and from its associated lakes and marshes.
Seawater lost to evaporation is not necessarily lost to power generation, however. Regional geography and prevailing winds guarantee that a large fraction of any seawater lost by evaporation will show up as increased precipitation over the Wasatch range in Utah or the western Rockies. Precipitation on the western slope of the Wasatch range flows back to the Great Basin, but the rest flows to the Colorado. It will still generate hydroelectric power; it’s just that the power will flow from the turbines of dams along the Colorado River.
Energy storage and distribution
While the direct hydroelectric power generating potential of the canal is interesting, its significance is mostly symbolic. It’s the fact that the energy cost of canal operation could be negative — that it could be a net energy producer, instead of yet another energy consumer. But the more important energy aspect of the canal is its energy storage potential. Each of the 100 or so level changes that the canal would require joins two large reservoirs at different elevations. Each level change is an opportunity for installation of large scale pumped hydroelectric storage.
When all the stations along the canal are operating in the same mode, each canal section below the upper end of the canal has equal amounts of seawater flowing into it from its neighbor on one end and out to its neighbor on the other end. Water is flowing through all sections, but the water level in each is unchanged. Only the large lakes at the top of the canal will be rising or falling. They effectively serve as the upper reservoir for a single large pumped storage system, whose lower end is at sea level.
The many saltwater lakes and marshes that in aggregate comprise the upper storage reservoir could easily cover 1,000 square miles in total. That’s four times larger than Lake Mead but would still be less than 1% of the state of Nevada. The lower reservoir is the Pacific Ocean. The vast size of the two reservoirs combined with the 4,000 foot elevation difference give the overall system an energy storage potential of 8,800 gigawatt-hours per meter of level change in the upper reservoir.
That storage capacity is so huge that even if the entire Southwest region that it served were to move to 100% intermittent renewables, the system could handle it. There’d be no need for any fossil fueled backing generation. Distribution of the pumping and generating capacity among hundreds of stations along the canal route plus hundreds of square miles of intermediate storage reservoirs would make the capacity extremely robust.
Last but not least (as they say) there is one final aspect of the canal project that I should mention. In fact, it’s the source of my title for this article.
A Pacific and Great Basin canal would have huge potential as a recreation resource. It would support boat and barge travel from the Pacific to Las Vegas and beyond to Reno. In this context, “barge” can include not just heavy freight carriers, but also passenger carriers that could be the equal in amenities, if not in size, to ocean cruise ships. Importantly, it could also include privately owned or rented “house barges” for families or small groups.
In Great Britain, the old system of canals had ceased to have much importance for commerce by the middle of the last century. Many of the smaller canals fell into disrepair and were closed, More recently there’s been a movement to restore and maintain them, due to the growing popularity of “narrow boating”. Narrow boats are live-aboard canal boats, the aquatic equivalent of RVs that are popular here. Their long narrow shape enables them to negotiate the smallest and narrowest of the old canals.
Canal boats of this sort would make appealing successors to highway RVs for leisurely family vacations in a post-carbon world. In the main canal, they’d be towed by tractor robots running on the tow paths for safe “hands off” cruising. But there could be pull-outs and side canals along the way that would lead to docks, stores, picnicking and hiking areas. The biggest of those side canals would undoubtedly lead to a Las Vegas boat park and marina. It might be adjacent to a “Venice in Vegas” complete with quaint canals, pedestrian bridges, and gondoliers.
The interesting thing about tying in to the Las Vegas and Reno hotel and hospitality industry is that the entire canal project could conceivably be funded as a way to attract visitors. The two cities have both tried to deemphasize gambling and increase their appeal for family vacations. They face stiff competition for tourist vacation dollars from states with coastal resorts. So imagine the effect if, on top of everything else these cities have to offer, they could advertise ocean sport fishing, scuba diving, and surfing on a 10,000 acre “ocean” in the middle of the desert.
My initial SWAG for the average cost of the canal proper is $5 million per mile, which is about 5 times higher than the average cost of a mile of rural interstate. For 700 miles of canal (which is about what it would take) that’s $3.5 billion. For 200 boat lifts at 2.5 million each, add $500 million; for 200 pumped hydroelectric stations, 100 MW capacity, $25 million each, another $2.5 billion. That looks like $6.5 billion. For comparison, The Las Vegas Convention and Visitors Authority reports that in 2015, gaming revenues for Clark County (where Vegas is located) were $9.6 billion.
My numbers are little more than semi-informed guessing. They could easily be off by a factor of two or more. But it’s an interesting thought that what would be the greatest carbon mitigation and ecology enhancement project ever attempted could be funded by the money that visitors to Clark county drop on the gaming tables there in a single year.