Trees, Dirt and Streams

Raw Dirt, Construction Site, George Mason University

Fairfax, VA, August 2010

©EOP

Yesterday afternoon, with the car thermometer registering 101 degrees F, I drove to the Vienna-Fairfax Metro station to pick up my wife. The area just south of the station looked radically different from its visage on my last trip to that station a few weeks earlier. A wooded area of several hectares had been stripped of all vegetation and was bare dirt being worked over by large construction machinery. It is the second property near the intersection of Route 29 and Nutley Street recently stripped of vegetation for new construction. In close proximity to the Metro Station, high density land uses are certainly justified, but was it necessary to clear away every last tree?

Fairfax County claims to be concerned about its tree cover, and has an ordinance to that end which, according to a news release from the County:

The Fairfax County Board of Supervisors adopted a tree preservation ordinance at its Oct. 15 (2007) meeting, protecting four types of trees. Under the new law, individual specimen, heritage, memorial or street trees can be protected from being cut down.

The new measure is not intended to protect large wooded tracts. Instead, the law only affects individual trees that property owners voluntarily agree to safeguard.

The board approved the law because even a single tree can benefit the environment. One mature tree with a 26-foot canopy can absorb the emissions of a vehicle driven 11,500 miles every year.

Homeowners, residents or groups can recommend individual trees for protection. After a public hearing, the board will approve the preservation of specific trees. Easements also may be required to protect a tree’s roots. If needed, property owners will donate the easements to the county.

As defined by the law, specimen trees are those that are notable in their size and quality for their species. Heritage trees have a historical or cultural interest. Memorial trees, as the name suggests, commemorate a memorial. Street trees are those that have been planted by the county on public rights of way.

There is a $2,500 fine for removing a protected tree without permission from the county. The ordinance takes effect immediately, and it has been added to the county code as chapter 120.

The preservation ordinance supports the county’s 30-Year Tree Canopy Goal adopted by the board in July. The county aims to blanket 45 percent of the county with tree cover by 2037. It is important to preserve existing trees because the county expects to lose 4 percent of its canopy during the next 30 years. To reach the goal, the county and the public also will have to plant an additional 2.6 million new trees.

Once achieved, the canopy goal is expected to save taxpayers money. The trees when matured should produce savings equivalent to $5.3 million for air pollution removal and $4.7 million in energy conservation every year. The additional canopy also will have the capacity to absorb more than 10 million pounds of carbon dioxide annually, which could eliminate the need for $1 million in greenhouse gas reduction services each year.

For more information about the new ordinance or 30-Year Tree Canopy Goal, call 703-324-1770, TTY 711, or visit www.fairfaxcounty.gov/dpwes/environmental/trees.htm.

It is interesting to note that the ordinance applies only to specific trees, not to forested areas. Since much of the woodland in the county is second growth, frequently a product of the reforestation of exhausted tobacco and other farm lands since the early and middle parts of the 20th century, that forest growing on nutrient poor land contains very few "specimen" trees notable for their age, girth, historical importance or beauty. Moreover, the ordinance only applies if land owners agree.

Fairfax City (under Virginia's peculiar local government system not a part of Fairfax County even though it is completely surrounded by it) calls itself a "Tree City USA." The City does indeed have many grand old trees and small woodlands, one of the strongest reasons attracting us to live here. Fairfax City has a stringent ordinance requiring City permission for tree removal. Despite that ordinance, a large parcel on the eastern edge of the City adjacent to Main Street (Route 236) was stripped of all vegetation for construction of residences just as the Cheney-Bush recession began in 2008, and the land has remained bare dirt since. As of a few weeks ago activity at the site has suggested that building will commence soon, but for about two years, through the melting snow of intense winter blizzards and torrential summer rainfall, dirt has eroded from that parcel into storm sewers flowing into nearby streams.

There has been a construction boom on the Fairfax campus of George Mason University over the past several years, and while some of that building used sites that previously had been parking lots, a major project at the north west corner of the campus, adjacent to Fairfax City, has also stripped several hectares of all vegetation. At the height of land, the site is the headwaters for a small stream which flows across the campus into a  holding pond. Despite some serious efforts to minimize erosion during construction, recent heavy rain has turned that pond a muddy brown, filling it with silt from the construction site a few hundred meters to its north. Eventually some of that silt will wash into the Occoquan, a primary source of water for the Virginia slurbs of Washington, DC.

Mason Pond, muddy after summer thunderstorms

George Mason University Campus, Fairfax

©EOP

Discussion of deforestation frequently focuses on the widespread cutting of trees in the Amazon Basin, in Brasil's Atlantic rain-forest, in Borneo or elsewhere in the tropics. In fact deforestation is a matter of consequence in many other areas. A recent Scientific American posting suggested that urban dwellers are driving deforestation. It was focusing on conditions in poorer countries where urban demand for food and fuel is leading to forest clearance, but the argument could well be extended to the United States where the demand for new slurban construction sites is causing large areas to be stripped of trees and other vegetation.

Fairfax City and County together have a large set of small-scale clearances which, in total, have a substantial impact on climate and water flow.The cooling effect of wooded land on nearby areas is well-known and easily demonstrated. On a hot and sunny summer day, walk from a copse of trees, even a small one, onto a patch of bare ground and the difference is instantly apparent. In a heat wave like the ones that have blighted the summer of 2010, a wooded area can be as much as 5 degrees C cooler than nearby open areas.

The effects of wooded land on water flow are a little more complicated. Forests even out the flow of streams, holding back some of it during and just after heavy rain and then releasing water in drier periods. The geology and soil of the Fairfax area and the torrential rains common with summer thunderstorms provide perfect conditions for filling streams with silt when the soil is bare.Wooded areas slow and filter the rapidly flowing rainwater draining after a storm, and they retain much of the material that could become silt. Water authorities in the county and nearby are well aware of the problems deforestation, and impermeable surfaces like paving  (a subject for another posting), create. Heavy rains in deforested areas lead to rapid runoff of silt loaded water into streams and reservoirs, while in a longish drought like the one in the first part of summer 2010, those streams and impoundments diminish or even dry up (their storage capacity getting smaller each storm as silt accumulates). When needed for water supply, that shrinkage can lead to sleepless nights for water managers after a long dry spell!

Minerals, Mining, and Water II: Hydraulic Gold Mining in California

"Hydraulic Mining, Behind the Pipes." 

Source: Central Pacific Railroad Photographic History Museum

Several months ago I purchased a copy of Isenberg, Andrew. 2006. Mining California: An Ecological History (New York: Hill & Wang, ISBN 0-8090-6932-6) at a used book sale. I have an ongoing if rarely pursued interest in the history of the far western US and in mining as a part of that history. Over the past few very hot days, stuck at home waiting for plumbers, I have been reading the fine and fascinating book. The early history of California is intimately tied to mining, and more than 100 years after the last hydraulic mines closed, scars remain on the landscapes of the Sierra Nevada foothills in "Gold Rush Country." Hydraulic mining techniques were widely used after about 1855, as water at high pressure was sent through nozzles pointed at loose sediments known or expected to contain gold nodules. The resulting mud was then run through screens and placers which separated out the valueless sand and gravel and left behind much of the heavier gold and other valuable minerals. (Not all of the gold was recovered, and there is a small but thriving present day business reprocessing the sand and gravel to recover the precious metals early mining left behind in deposits of sand and gravel like the one shown in th photo at the end of this posting).

In order to feed the high pressure nozzles, a great deal of water was needed, and to assure pressures high enough to wash the loose sediments into sluices, dams and aqueducts were built higher up on the streams. Not a few of those dams were poorly engineered or shoddily constructed, and there were several catastrophic dam breaks flooding downstream areas and killing miners unlucky enough to be in the path of the water flowing downhill. Vast quantities of materials were displaced by the technique, and among several consequences rivers once running clear were turned into thin mud flows. Salmon runs in those rivers ended, and San Francisco Bay received large quantities of silt. The already flood prone Sacramento and San Joaquin Rivers, near sea level in their final kilometers where they meet in the delta, flooded more often and more catastrophically. Closer to the mines, towns had to find alternate water sources as the water was too muddy and contained toxic metals dissolved at and downstream from the workings. Hydraulic mining was finally banned in 1884 by a decision of the federal 9th Circuit Court.

Traces of mining history remain in the water supply of those streams where water melted from the Sierra Nevada snowpack and flowing through the rivers of the gold region was used in hydraulic mining and today is the water supply for much of California's 37 million people, its industry, and its agriculture. Gold and other precious metals were the magnets attracting miners to the state, but California was also one of the world's major producers of mercury, chemical symbol Hg, at the New Almaden mine in the Coast Range mountains near present day San José in Santa Clara County and at New Idria in San Benito County about 100 km south. Mercury in most of its common forms is toxic to humans, domestic animals, and much plant life, and in some forms only a small exposure to mercury is needed to have toxic effect.

New Almaden Smelting Works, 1863

Source: Wikipedia

The proximity of the mercury source, it is less than 500 km between the New Almaden mine and most of the gold workings in the Sierra foothills, made an amalgamation process of mining popular. Gold (as well as silver and several other valuable metals) will dissolve in mercury. Once a quantity of ore is dissolved in a flask of mercury, distillation drives off the mercury, which can then be condensed and reused, leaving behind the desired gold. While the mercury fumes were highly toxic to anyone who happened to breathe them during the distillation, the process was inexpensive and thus popular. It was far from perfect, and lumps of mercury contaminated material were deposited in the detritus of hydraulic (and other) mines. Over time some of that mercury has leeched into the flowing waters of streams and contaminates nearby rivers. Occasionally health authorities ban use of the water for domestic purposes because of mercury contamination. In California with perennial water supply problems, mercury contamination of some of its more reliable streams remains a serious and ongoing problem.

Cone of hydraulic tailings on Wedge Gulch, The tailings were partly caught by a restraining dam, and the mass afterward eroded when the dam gave out. Big Trees quadrangle, Calaveras County, California. 1905. Published as plate 5-A in U.S. Geological Survey. Professional paper 105, 1917.

Dams - The Fascination of the Immense

Three Gorges Dam and Reservoir, Yangtze River, China, June 2009

NASA Earth Observatory

Standing on the Nevada shore (being careful not to cross over into Arizona where one might be arrested as an enemy alien) and admiring the sleek arch and art deco works of the great Boulder Dam (aka Hoover Dam) across the Colorado it is difficult not to be awed at the power of humanity. Many years ago a famous architect working on one of the megalomaniac urban design projects for which his field is notorious said something to the effect "make no little plans for they have no power to stir men's blood."  The design project thankfully came to naught, but his statement still has power. Nowhere is that more true than in the construction of huge dams. The icons of the New Deal in the United States are large dams, from the impressive structures on the Tennessee River and its tributaries as a part of the TVA to the grandest two of all, Boulder Dam on the Colorado and Grand Coulée on the Columbia. Subsequently dictators, autocrats, and even a few leaders in nominally democratic states have ordered construction of immense dams including ones on most of Russia's great rivers, on the Nile, on the Paraná, and on China's Yangtze. The dams have been variously designed to prevent flooding, to improve navigation, to store water for irrigation, and to produce electricity, with most of them intended to do at least two of that magic four.

Immense dams have come with a set of problems, however. Blocking the normal flow of the river, they serve also to block the flow of silt, and it collects behind the dams. The Aswan Dams on the Nile have blocked the flow of silt onto Egypt's riverine fields. While they generate a huge amount of electricity, much of that is used to produce fertilizer to take the place of the silt that once made the Nile Valley a breadbasket. Meanwhile the Nile delta is rapidly receding (and Egypt is getting smaller) as it is not receiving silt from upstream. The huge dams on the Colorado in the United States are also rapidly silting, though the low flows of the past decade mean that silting has been slowed. Eventually silting will render the dams useless for water storage and degrade or eliminate their benefits of flood control, navigation, irrigation water storage, and hydroelectric production. All dams are subject to silting, but the problem is especially great on rivers like the Colorado and the Nile whose headwaters include areas of easily eroded materials like sandstone.

A motto of the early Soviet experiment was "socialism plus electricity equals communism," and the construction of immense hydroelectric dams was a key goal throughout the ill-fated Leninist-Stalinist pseudo socialist experiment. A year ago Sayano–Shushenskaya Dam, one of the huge dams in Russia built by the Soviets to produce electricity, experienced a large explosion in its powerhouse, flooding the powerhouse and among other things sending a plume of lubricant oil down the Yenisei toward the Arctic, destroying several turbines, and killing at least 74 people. For a time Russia's electricity supply was reduced by a sizable percentage, and several key export industries, including aluminum production, were harmed. The flooded powerhouse had ot be closed and repaired, a process still ongoing, though the dam is again producing electricity.

Yesterday evening BBC News America had a story on flooding in China, high water on the Yangtze below the world's largest dam. One of the functions of the dam was to prevent downstream flooding, but it would seem it is having almost the opposite result. At least according to Chinese authorities the dam itself, also intended to  is secure  Earlier it was discovered that large dams in China were creating earthquakes and might have been directly responsible for several large and deadly temblors.

One must hope the Three Gorges Dam is the final immense dam built on earth to improve navigation on the Yangtze, to store water for downstream irrigation, and to produce hydroelectricity. Given the predilictions of totalitarian governments that may be a vain hope, but accumulated evidence makes it clear that huge dams create problems far greater than those they are intended to resolve.

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