Tag Archives: hydropower

Colorado River

Extended Drought in Southwestern US

One of the projections of climate change due to global warming is alterations in rainfall patterns. Warmer air will hold more moisture so one might think that global warming will cause more rainfall and generally that is true overall, but another feature of global warming is a redistribution of rainfall, more falling on the coasts and less in the continental interior.

Additionally, the rainfall patterns are predicted to change to more intense storms where larger amounts of rain occur over shorter time spans. Heavy rains mean more runoff, hence less water available for the myriad of uses we depend on – energy production, agriculture, industry, recreation and most importantly drinking water.

>The Colorado River and its tributaries drain a basin of a quarter million square miles. Forty million people in six western states [Colorado, New Mexico, Utah, Wyoming, Nevada, Arizona] are directly in the line of fire of climate change. For millions of years the Colorado has flowed from the upper reaches of the Rockies to a large delta at its confluence with the Gulf of California.

Not so much any more. A combination of drought and pressure on the river from agriculture and burgeoning cities has reduced the flow to the point that in recent years the Colorado no longer reaches the sea. Virtually every drop is removed for irrigation in the Imperial Valley of California, to cool coal-fired power plants around the Four Corners area, and to water golf courses in Phoenix.

Global warming and the attendant climate change is predicted to decrease precipitation by twenty percent in the watershed over the next forty years. This will greatly exacerbate the issue of the availability of water in the southwest. The water level of Lake Powell,

Lake Powell on Colorado River

Lake Powell on Colorado River

formed by the construction of the Hoover Dam is at an all time low, some 120 feet below its high of a decade ago. Images show what appears to be a “bathtub ring” on sandstone bluffs along the lakeside.

Another distressed southwestern watershed is the almost two thousand mile long Rio Grande which demarks much of the border between the US and Mexico. The two hundred thousand square mile basin has been stressed by a decade long drought, and it appears to be getting worse due to global warming. Two significant reservoirs, Elephant Butte and Caballo are at less than ten per cent capacity.

Elephant butte Reservoir

Elephant butte Reservoir

Like the Colorado, the Rio Grande doesn’t make it to the sea. What little flow exists is removed, mainly for irrigation. The flow essentially ends by the time it reaches Presidio, TX.  Other significant water courses in China, India and Australia are distressed to the point of no exit flows. The problems are real and worsening with increasing population demand and climate change.

Global warming is real, we are causing it and we need to address how to stop,even reversed it, in addition to the immediate need for adaptation to the new climate we are forcing.

Hydropower in Arkansas

Electricity production in Arkansas is similar by source to the rest of the country. For Arkansas, the percentages are coal, 47 percent, nuclear 25 percent, natural gas 15 percent; and hydroelectric, 10 percent. Sustainable sources such as wind and solar electric represent only a fraction of a percent.

An ideal power source would be sustainable, clean and available when needed in the amounts needed. Hydroelectric energy production comes close to this ideal.

Facilities range in size from the generators at Remmel Dam on Lake Catherine with a 9.3 megawatt capacity to the dam at Bull Shoals with 380 megawatts. The dam on Lake Dardanelle comes in second with a capacity of 161 megawatts. Total hydropower in Arkansas is 1,374 megawatts from 15 facilities.

Discussions about energy supplies can get terribly muddled without a clear understanding of three terms: power, energy and capacity factor. Power is the ability to do work, energy is the actual work done and capacity factor is the amount of time actually doing the work.

An example may be helpful. The generators on Lake Dardanelle have a rating of 161 megawatts (power). When the generators run at this rate for one hour, they will produce 161 megawatt-hours (energy). To get the maximum possible annual energy produced, simply multiply by the number of hours in a year.

But they don’t run all the time. Too much water due to heavy upstream rainfall, or too little water, or even varying demands limit the amount of time the dam is generating (capacity factor). The average capacity factor for hydropower in Arkansas is about .47. This means on an annual basis, hydroelectric facilities produce about 47 percent of the energy theoretically possible.

Capacity factors for other energy sources for comparison are about 90 percent for nuclear and 17 percent for solar electric systems. A high capacity factor is not necessarily good, nor a low one bad as the important thing is matching supply with demand. A large reservoir like Bull Shoals is valuable as both long term and short term energy storage. Water accumulates during the winter when there is lower demand for electricity and then is released on hot afternoons in the summer to generate power “on demand.”

The ability to rapidly increase power production is important to meet peak demands. On the other hand, nuclear power reactors are better at providing base load power due to the fact that they run best a full power and are not capable of powering up and down to meet variable loads.

Hydropower is not a perfect solution due to several drawbacks. To be economically practical, they need to be large; therefore, large amounts of land are put underwater. More than 5 million people were displaced by the construction of the Three Gorges Dam in China. The remains of an unusual resort community called Monte Ne lies submerged under Beaver Lake. Occasional mechanical failures of dams have had catastrophic results, and reservoirs have limited lifetimes due to silt accumulation which ultimately limits power production.

Virtually all suitable sites for hydropower in Arkansas have been used. The last battle for a large reservoir, at Gilbert, resulted in the creation of the Buffalo National River. It is over 135 miles and the first federally protected river with the highest bluff and the tallest waterfall between the Rockies and the Appalachians.