water supply

Desalination of Sea Water Can Augment Our Water Supply Without Harming Sea Life

Since the Colorado River may not supply us with all the water we need, we should turn to the oceans.

Desalination of sea water can produce the freshwater we need to augment our natural supplies. The most common method is reverse osmosis where the sea water is forced through a semi-permeable membrane which removes the salt.

However, the process is energy intensive which some environmentalists claim will put more dread carbon dioxide into the atmosphere if the electricity comes from fossil-fuels. That can be solved by powering the plants with small, dedicated nuclear generators. (Powering such plants with wind or solar energy will make freshwater production intermittent and unpredictable.)

The other claim by some environmentalists is that the effluent from the desalinization process, very salty brine, is harmful to wildlife. A new study shows this concern is overblown.

A seven-year study, jointly conducted by Southern Cross University and the University of New South Wales at the Sydney (Australia) desalination plant found that when the plant was in operation, fish population in the area almost tripled. Fish populations decreased to normal when the plant was not operating. The Sydney plant has a capacity of producing 74,000 acre-feet of water per year.

Lead researcher Professor Brendan Kelaher said, “At the start of this project, we thought the hypersaline brine would negatively impact fish life. We were surprised and impressed at the clear positive effect on the abundance of fish, as well as the numbers of fish species. Importantly, the positive effects on fish life also included a 133 per cent increase in fish targeted by commercial and recreational fishers. As to why fish like it so much, we think they might be responding to turbulence created by dynamic mixing associated with the high-pressure release of the brine. However, more research is needed.” (Source) The report mentions no detrimental effects on fish or other sea life. The research was published in the journal Environmental Science & Technology. http://pubs.acs.org/doi/abs/10.1021/acs.est.9b03565

I did try to find information on negative impacts to marine life of concentrated brine being pumped into the ocean, but all I could find was speculation, no actual physical evidence. Apparently harm is minimal. As noted by marine biologist Daniel Cartamil of Scripps Institution of Oceanography, intake water may contain tiny organisms (plankton), including the eggs and larvae of marine life. None of these organisms survive their journey through the plant. However, this entrainment typically accounts for only about 1 percent or 2 percent of plankton mortality in a given area. Cartamil says this about the salty brine discharge: “In theory, marine life (particularly plankton) could be harmed by prolonged exposure to salinity levels higher than those they normally cope with. The most common solution to this problem is to mix the brine back into the seawater with high-speed jets, a process so efficient that salinity levels are effectively back to normal within 100 feet of the release point.” (Source)

Perhaps Arizona, California, and Mexico will take heart and build more modern desalination plants near the Sea of Cortez and the Pacific Ocean to help ease our dependence on the Colorado River. Some of the salt could be recovered for industrial applications. There is a desalination plant in Yuma, built in 1992 to treat agricultural runoff and conserve water in Lake Mead. But its technology is outdated. There is also a desalination plant just north of San Diego with a capacity of 56,000 acre-feet per year. Building more and bigger desalination plants powered by nuclear generators is technologically feasible but politically problematic.

Articles on small nuclear reactors:

A New Type of Molten Salt Nuclear Reactor

Small Modular Reactor by Westinghouse

What are small modular nuclear reactors, and why are three provinces uniting to build them?

Advanced Small Modular Reactors

Forest thinning may increase runoff and supplement our water supply

Thinning of southwestern forests, partly to curb devastating forest fires, has long been a controversial subject. In general, forest thinning has been opposed by environmental groups.

Now, however, a new study (“Effects of Climate Variability and Accelerated Forest Thinning on Watershed-Scale Runoff in Southwestern USA Ponderosa Pine Forests” published October 22, 2014) conducted by The Nature Conservancy and Northern Arizona University recommends accelerated forest thinning by mechanical means and controlled burns in central and northern Arizona forests. The study estimates that such thinning will increase runoff by about 20 percent, add to our water supply, and make forests more resilient. You can read the entire study here.

Forest thinning study area

The study abstract reads:

The recent mortality of up to 20% of forests and woodlands in the southwestern United States, along with declining stream flows and projected future water shortages, heightens the need to understand how management practices can enhance forest resilience and functioning under unprecedented scales of drought and wildfire. To address this challenge, a combination of mechanical thinning and fire treatments are planned for 238,000 hectares (588,000 acres) of ponderosa pine (Pinus ponderosa) forests across central Arizona, USA. Mechanical thinning can increase runoff at fine scales, as well as reduce fire risk and tree water stress during drought, but the effects of this practice have not been studied at scales commensurate with recent forest disturbances or under a highly variable climate. Modifying a historical runoff model, we constructed scenarios to estimate increases in runoff from thinning ponderosa pine at the landscape and watershed scales based on driving variables: pace, extent and intensity of forest treatments and variability in winter precipitation. We found that runoff on thinned forests was about 20% greater than unthinned forests, regardless of whether treatments occurred in a drought or pluvial period. The magnitude of this increase is similar to observed declines in snowpack for the region, suggesting that accelerated thinning may lessen runoff losses due to warming effects. Gains in runoff were temporary (six years after treatment) and modest when compared to mean annual runoff from the study watersheds (0–3%). Nonetheless gains observed during drought periods could play a role in augmenting river flows on a seasonal basis, improving conditions for water-dependent natural resources, as well as benefit water supplies for downstream communities. Results of this study and others suggest that accelerated forest thinning at large scales could improve the water balance and resilience of forests and sustain the ecosystem services they provide.

The study also notes that in “ponderosa pine forests of central Arizona, stand densities range from 2 to 44 times greater than during pre-settlement conditions” and all that extra foliage sucks up water and loses it through evapotranspiration, thereby decreasing the availability of water for downstream users and wildlife.

Congress has authorized a program called the Four Forest Restoration Initiative (4FRI) that will accelerate the use of mechanical thinning and prescribed burns across four national forests, treating 238,000 ha (588,000 acres) in the first analysis area over the next 10 years. That program should be expanded.

Arizona may have larger potable groundwater resource

Southern Arizona gets about 43% of its water by pumping groundwater aquifers.  The geology is well-suit for this because Southern Arizona is in the Basin and Range province which contains very deep, fault-bounded valleys.  In some places, bedrock is as much as 15,000 feet below the surface.   Portions of the Tucson and Avra valleys are over 8,000 feet down to bedrock.  Such valleys are filled with alluvium and water.

Figure-1-salinity-statewide-map-v3

Currently, water for drinking exploits aquifers down to a depth of about 1,200 feet.  Generally water below that depth is too salty for drinking.

Following up on two previous studies, Estimated Depth to Bedrock in Arizona and Preliminary evaluation of Cenozoic Basins in Arizona for CO2 sequestration Potential, the Arizona Geological Survey in a new study, examined the salinities of Arizona groundwater.  The study is A Summary of Salinities in Arizona’s Deep Groundwater, Arizona Geological Survey Open-File Report, OFR-12-26.

As part of that study, geologists of the Arizona Geological Survey (AZGS) reviewed geophysical well logs to catalog the concentration of total dissolved solids (TDS, i.e., salinity) of 270 water wells.  This included all water wells that penetrated deeper than about 2,600 feet, which is the minimum depth necessary to sequester carbon dioxide.

Among the results of that study, AZGS found that on the Colorado Plateau and in the Basin and Range province, there are some areas where “Fresh water can extend as deep as 5,000 feet (1,500 m), but below 6,600 feet (2,000 m) only brackish or saline groundwater was encountered..”   Water is considered “fresh” if it contains less than 1,000 ppm (parts per million) TDS.  Water is “brackish” if TDS are 1,000- to 30,000 ppm.  “Saline” water contains greater than 30,000 ppm TDS.  Sea water is about 35,000 ppm TDS.

This means that we may be able to extract drinking water from deeper aquifers in some areas.

See also:

Water Supply and Demand in Tucson

How much water is there?

Trends in groundwater levels around Tucson

Hydroclimate of northeast US highly sensitive to solar forcing

A new paper in Geophysical Research Letters presents “a 6800–year, decadally-resolved biomarker and multidecadally-resolved hydrogen isotope record of hydroclimate from a coastal Maine peatland.”

The researchers say that “Regional moisture balance responds strongly and consistently to solar forcing at centennial to millennial time scales, with solar minima concurrent with wet conditions. We propose that the Arctic/North Atlantic Oscillation (AO/NAO) can amplify small solar fluctuations, producing the reconstructed hydrological variations.”  Note that this method of solar amplification is supported by several studies in Europe.  The cycles and amplifications are also supported by independent lake sediment and speleothem (cave formation) data.

The researchers go on to say, “The Sun may be entering a weak phase, analogous to the Maunder minimum, which could lead to more frequent flooding in the northeastern US at this multidecadal timescale.”

Reference:

Nichols, J. E., and Y. Huang, 2012, Hydroclimate of the northeastern United States is highly sensitive to solar forcing, Geophys. Res. Lett., 39, L04707, doi:10.1029/2011GL050720.

[Link to full paper]

 

See also:

Weather extremes and global warming – no increasing trend

 

How much water is there?

The answer depends in part on how much you are willing to pay. There continues to be some valid concern about our water supply. These concerns generally cite our current drought conditions and population growth. Tony Davis of the Arizona Daily Star has written a series of articles on the subject, articles that generally sound an alarm. For instance, see Tucson’s source of water runs low and Contrasting views on what to do about dwindling water .

To put such articles in perspective, however, consider this:

The Tucson area currently uses about 350,000 acre-feet of water per year. An acre-foot is 325,851 gallons, enough to supply three-to six family residences for a year (the number of residences depends on who’s doing the estimation). For that 350,000 acre-feet of current usage, we withdraw about 256,000 acre-feet from our groundwater supply. The Central Arizona Project (CAP) provides about 65,000 acre-feet and the rest is from use of effluent and incidental recharge. Natural recharge to the aquifers is about 60,000 acre-feet per year, much less than the amount we withdraw.

Estimates from the University of Arizona imply that our groundwater supply, at projected rates of usage, represents about a 200-year supply. Our CAP allocation is 314,000 acre-feet per year. That would seem to cover our needs, but the CAP supply is subject to natural variation of droughts, and the whims of politics. For more details, please read my blog from last June: Water Supply and Demand in Tucson. For a perspective on droughts, see my article: Drought in the West.

Our CAP supply is drawn from the Colorado River. Currently our Colorado River reservoirs stand at 55% capacity, the same as last year at this time. We are not gaining on the amount stored because water released for electrical generation and river health about equals inflow to the system. See: Bureau of Reclamation weekly water report. See also: Bureau of Reclamation forecasted use for 2010. In contrast, the Salt River system, supplying Phoenix, stands at 97% capacity. The BR report says that our “water year” precipitation is 82% of normal in the Colorado River basin and 122% of normal in the Gila River system. Snowpack is put at 83% and 244% respectively.

The point of this article is that our water policy must be based on facts rather than on perceptions. Conservation measures must also be based on facts rather than on “feel-good” ideas of the day.

The groundwater supply mentioned above counts just the aquifers down to about 1200 feet, but depth to bedrock in the Tucson and Avra Valleys is as much as 15,000 feet deep in places, so the valleys contain more water. That deeper water, however, would be more expensive to pump and process.

A related, but important concern is not just the ultimate water resource, but also the distribution system, how to get the water to the customer. Current peak summer water demand in Tucson is greater than maximum well pumping capacity of 143 million gallons per day. How much water is there? That depends on how much you are willing to pay.