After my last posting on Colorado Hydroelectric power, I got a comment related to the fact that there were several hydro plants on the Big Thompson River. I started to do some more research eventually culminating with a visit to canyon yesterday to do some firsthand investigation on the subject.

There are actually two hydro plants situated on the Big Thompson River. One is part of the Colorado Big Thompson (C-BT) project and is located down by the mouth of the canyon near the Dam Store. It’s called the Big Thompson Power Plant and was accounted for in my last posting. It is the smallest of all the C-BT generating plants (4.8 MW) and is only operated during the runoff season from May through September. There is a dam just upriver from it, but the water from that dam is not used to power it. Instead, it is powered by a penstock with 180’of head that comes from the Charles Hansen Feeder canal. The canal runs across Highway 34 via an inverted siphon. That’s the pipe you see when you enter the canyon.

This is the 4.8 MW Big Thompson hydro plant. The large overhead structure is a crane for servicing the generator.

The water in the Charles Hansen Feeder canal can be augmented with the Big Thompson River by a diversion dam located about a mile up the canyon. This small dam feeds water into the Dille tunnel which goes through a mile of solid rock to meet up with the Charles Hansen Feeder canal just south of the inverted siphon. You’ll notice that the pipe is quite a bit lower than the open canal sections that run on either side of it. I’ve included a Google Earth 3D perspective of this phenomenon. I never understood what that pipe did until I flew over it and then it was like a lightbulb going off in my head. I suppose an aqueduct that ran across the canyon at the canal elevation would have cost much more to construct than this inverted siphon. The Charles Hansen canal is used to fill Horsetooth Reservoir with C-BT water.

The Big Thompson power plant’s penstock is formed by a rectangular concrete chute that runs down from the canal on the south side of the highway 34 and is piped under the highway and over to the generating station. In addition, some of the canal water can be simply dumped into the Big Thompson River depending on how they want to move flow along the C-BT project.

This is a Google Earth 3D view of the mouth of the Big Thompson canyon. You can see that the Charles Hansen canal is much higher in elevation than the pipe that crosses the highway. The power plant water inlet comes from the top of the canal on the left side of the canyon.

I spoke yesterday with a very nice woman from the Bureau of Reclamation by the name of Kara Lamb who posts frequently to a forum sponsored by Mountainbuzz. This forum is monitored by white water kayakers with rapt attention to check flow rates on the Big Thompson River. That way they know when it’s time to ditch work and do some kayaking. Flow rates are changed periodically to send water to where it’s needed and so the volumetric flow can vary unpredictably and thus is important for kayakers to check the forum to see when the water levels are suitable for kayaking. Kara is very knowledgeable about the C-BT project and in the course of one of her postings, she mentioned another power plant on the river owned by the city of Loveland. The power plant she referred to is the Idlewilde Hydro Plant located in Viestenz-Smith Park. This power plant is fed via a penstock from the Idlewilde Reservoir which is located about 2 miles upriver from the plant. The plant is very easy to overlook because it’s not very big and there is not much equipment around it to suggest it’s a power plant. It could easily be mistaken for a maintenance building.

I found in searching around that there was a trail that ran up the canyon on the opposite side from the park called the Foothills Nature Trail that was said to have a few exposed sections of the penstock, which is otherwise buried for the 2 mile distance it runs to the Idlewilde reservoir. I hiked this trail yesterday and took a picture of the metal pipe. It is 3’ in diameter and was originally made of wood back when it was first constructed in 1920’s.

A small exposed section of the Idlewilde Dam-Power Plant penstock. It runs 2 miles, mostly underground from the reservoir to the power plant and can carry 74 cfs of water.

I couldn’t find any information regarding the amount of water flow through the penstock or generating capacity of the Idlewilde plant on the Internet so I went to the park and found some posters that explained a little more about its tumultous history and other interesting facts. The generators inside the building were rated at 900KW which is enough to supply electricity to about 900 homes. Back in the days when the only use for electricity was lighting, this hydro plant could supply a substantial portion of Loveland’s electricity needs.

At 900KW, the Idlewilde hydroelectric plant much smaller than any of the hydro plants that are part of the CB-T project. But since it is not a technically a part of the C-BT project, there is no information about it on the C-BT web pages. The entire facility was completely wiped out in the Big Thompson flood of 1976 and the remnants of the 3 original generators are on display in the park. In the 1980s, the plant was rebuilt and the generators were replaced
with 2 turbines with the same generating capacity. The generating station subsequently returns all the water it receives from the penstock to the river just downstream from the hydro plant.

I also found on the Bureau of Reclamation website that my estimate of 50% for the capacity factor may be too high for several of the C-BT power plants, particularly the Big Thompson Power Plant since it only operates from May-Sept each year. Thus, its capacity factor is only around 20% of its 4.8MW nameplate value. I think that when the river flow is low like it is now in January (~20 cfs), only a portion of the rated power could be generated by the Idlewilde plant. In other words, a 74 cfs diversion flow from the Idlewilde Dam could not be sustained in the winter months and thus it would have to run at reduced capacity. But I was able to hear the generators running, so it appears to be generating at least some electricity year-round.

In talking with Kara, she mentioned that there have been various proposals to add hydro capacity over the years, such as at the outlet of the Olympus Dam in Estes Park, as well as the outlets of Carter Lake and Horsetooth Reservoir. However, these never seem to move forward due to their economics. They just wouldn’t generate enough power to cover their construction and operating expenses.

The more I research the C-BT project, the more impressed I am with the engineering and foresight that went into it. In addition to augmenting the water supply on the Front Range with more capacity that the Big Thompson and Poudre Rivers combined, the designers did an excellent job at extracting all of the available hydro power from the water with minimal environmental impact. It’s hard to fathom that much of the project was implemented more than 60 years ago.

My conclusion is still the same as my original assessment, that is, since now I know that 2 miles of the interior of the Big Thompson canyon essentially has its hydro power harvested to produce less than 1MW of power, the total capacity of the 20 mile stretch of canyon would account for no more than 12 MW of generating capacity which is certainly not enough to justify the environmental impact or economics of pursuing it.

My friend Bevan asked me recently why we don’t see more hydroelectricity projects being developed. I replied, “All available hydroelectricity that can be developed has already been developed”, hoping it didn’t sound too much like the unfortunate 19th century quote attributed to Charles Duell about how everything that can be invented has already been invented. Despite my interest in renewable energy, I had not thought very much about hydroelectric power since I have long assumed that if someone could have built another dam on any existing waterway and placed a generating turbine at the bottom of it, it would have been done decades ago.

Bevan responded, “Well, how about the Big Thompson River which flows unimpeded down a canyon for many miles and has no hydro generating stations along it?” I began to wonder if we had been avoiding employing a source of clean and renewable energy simply because of its environmental impacts, as often seems to be the case. I thought, “If the Big Thompson canyon could be dammed, how much hydroelectric power could it produce?” Please note I’m not suggesting that anyone actually do this. It’s one of the most naturally beautiful and accessible canyons in Colorado and even if it could supply enough energy to solve the entire world’s energy needs, it probably still would never be approved due to opposition by those who would like to keep the canyon and river in their natural states. I am just trying to satisfy a curiosity I have.

Often times, putting up dams on rivers is resisted even more vehemently by environmentalists than constructing fossil fuel-burning plants. The concerns range from the people who are displaced by lakes that are created by the dams to fish species that can no longer reach the river’s head waters to breed. Dams have some other benefits such as flood and drought control, but those may be overshadowed by the safety concerns of a dam breaking and causing flooding and destruction. So despite its environmentally-friendly electric power generation, hydroelectric power has other environmental impacts that can limit its acceptance.

A few months ago I took a clean energy class through CSU. One of the classes met at the offices of the Platte River Power Authority, a co-op power company that supplies electricity to the cities of Fort Collins, Loveland, Longmont and Estes Park. The PRPA gets about 20% of its power from hydroelectricity. While touring the grid control facility, I saw a lot of generating stations on the large control board. Among them were several hydro generating stations located west of Fort Collins. I realized that I had somehow overlooked these generating stations in my travels, although I’m sure I had driven by them or flown over them on many occasions. Upon doing some research into the topic, I found that the hydroelectric generating stations monitored by the PRPA are powered with water that is diverted from the western slope. Through a series of tunnels, canals, and siphons, nearly all of the 260,000 acre feet of water diverted annually from the western slope has its energy converted to electricity by a series of power hydroelectric generating facilities, most of which are easy to overlook.

The means to divert the water from the western slope is called the Colorado Big Thompson (C-BT) Project. It is one of the largest and most complex natural resource developments ever undertaken by the Bureau of Reclamation. There are more than 100 structures comprising this project which you can read about here.

The most important part of the project is the Alva B. Adams tunnel that directs water from Grand Lake on the western slope to the eastern slope of the Rocky Mountains. The tunnel is 13 miles long and goes through solid rock under the continental divide. The water eventually finds its way into several large man-made reservoirs, the largest two being Carter Lake and Horsetooth Reservoir which are situated in the foothills along the Front Range. Prior to arriving at these reservoirs, the water flows through 5 hydroelectric generating stations. I’ve listed them and their capacities in this table:

Unlike many of the hydro generating stations you find on large rivers, the ones that are part of the Colorado Big Thompson Project are small stations located at the end of long pipes called penstocks, which are large diameter tubes connected to the upstream water source.

Energy contained in water is proportional to both the water’s pressure and flow rate. This energy is converted to electric power through a turbine-generator. Available water flow is usually dictated by nature by the region’s snowfall and rainfall. Pressure, however, can be adjusted. To increase the pressure, it’s necessary to increase the depth of water, also known as its ‘head’. Water pressure increases about 1 psi per 2.3 foot of head, and as a result, you can see that the generating stations with the higher penstocks in the table above produce much more power. One way to get more pressure is to construct a very tall dam. Another way is to construct a relatively shallow dam and put the generating facility at lower elevation and connect the dam and generating station with a penstock. You need to constrain the water in the penstock that runs downhill to the generating station which has the effect of greatly increasing its pressure. Sometimes these large diameter pipes are buried, and other times they are exposed. You can see them exposed in several places in Colorado Big Thompson Project, such as above and below Mary’s Lake just south of Estes Park. There you can see a long sections pipes running down a mountainside. At the bottom of the upper penstock, you’ll find Mary’s Lake generating station. A similar penstock runs partially underground and partially above ground from Mary’s Lake to the east side of Estes Lake, where you will find Estes Park generating station.

I am missing one C-BT power plant in my list above because it is located on the western slope, a 21.6 MW generating facility on the Green M
ountain Reservoir. Although it is technically part of the C-BT project, I didn’t include it because I was interested in figuring out how much power is generated from this diversion project from water flow to the east side of the continental divide. I was also curious about how much water flowed to the east side of the continental divide through the tunnel and how it compared with the normal Big Thompson River flow. In other words, just how much water do we import from the western slope?

Wikipedia lists the average flow rate of the Big Thompson River to be 72.5 cu. ft/sec where it exits the Big Thompson Canyon. The Alva B. Adams tunnel can handle a flow rate of 550 cu. ft/sec. It runs at about 84% capacity on an annual basis which means that it has an annual average flow of 460 cu ft./sec. I was very surprised by this number. This means the tunnel provides more than 6 times as much water flow as the Big Thompson River provides on an annual basis.

The total maximum generating capacity of the 5 hydro plants that I’ve listed in the table is 162.5 MW. A reasonable capacity factor for hydroelectric generating plants is 50% so we can assume that the average annual generating capacity of these stations is about 81 MW or 710 million kWh per year.

So, where am I going with all this? I’m trying to figure out how much energy could be obtained if we were to convert all the flow of the Big Thompson canyon using several large dams or a series of smaller dams with penstocks connected to generating stations. Based on the differences in flow rates between the Big Thompson River and the diverted flow through the Alva B. Adams tunnel, which is a factor of 6.4 greater, I would estimate that the amount of power available from the Big Thompson River would be around 12 MW, again assuming a capacity factor of 50%. I figure that the head of each flow is the same, and thus the flow rate difference means that the Big Thompson would generate about 16% (1/6.4) of the capacity of the C-BT generating stations if it were to all be converted to electricity. That’s enough to power 12,000 homes. This sounds like a lot, but to really put it in perspective, this is only around 2% of the capacity of a typical fossil fuel generating plant. For example, the Rawhide Power Plant north of Fort Collins which is a coal/gas plant can generate 522 MW. The Fort St. Vrain power plant south of Greeley which uses natural gas can generate 720 MW. Nuclear plants typically have capacities of 1000 MW or more, with the largest one capable of generating more than 8000 MW. When you talk about power in those quantities, 12 MW seems like a drop in the bucket.

It would appear that the amount of power available from the Big Thompson River is so small as to not make it worth the investment even if there were no environmental concerns. The construction costs would be quite substantial, considering the impact to the region such a project would cause. It would require moving many homes and businesses as well as the highway that runs through the canyon.

Rivers in the Colorado are much smaller than the ones you find in the eastern and pacific northwestern parts of the United States. In fact, based on flow rate, they would probably only qualify as creeks in other parts of the country. On the lower section of the Susquehanna River in Pennsylvania, there are 3 hydroelectric dams in a span of 21 miles that combine to generate more than 1,000 MW of hydroelectric power. But with an average flow rate of 40,000 cu ft/sec, the Susquehanna River has 500 times the flow of the Big Thompson River.

The largest hydroelectric generating project in the world is currently under construction in China. The Three Gorges Project will have an output of 22,000 MW and will thus qualify as the largest electrical generating plant in the world of any kind. It’s not without its environmental impacts, however. Nearly 1.4 million people had to be moved in order to fill the lake behind the dam. I suppose eminent domain may work a little differently in China than it does in the U.S.. I can’t conceive of any public works program that could displace people on that scale in the U.S. or any other country for that matter.

Hydroelectric power is one of the oldest and largest sources of renewable energy available today. Its output doesn’t vary as much as other renewable energy sources like wind or solar. It even offers the potential for energy storage to allow for peak demand-shifting. However, I don’t think that it can be expanded significantly from its current state, except perhaps in a few geographies around the world that are underdeveloped by western standards.