Nov 23, 2011, 7:24 AM
Post #5 of 5
Did you know that more water is lost to evapaoration than GDL sucks away? In about 2002, when the lake was very low, the government forced release of water from the dams, private and governmental, legal and illegal. Of course, a part was due to the fact that the dams were full and at risk of washing a lot of bodies into the lake. And a lot of chemicals were washed from the farmers fertilizing the lirio. That too was a mess. There should be no problem with a second drain off from GDL as far as lake level is concerned. This has been confirmed by a volunteer civil engineer from the US. Below I have copied a document previously circulated by Dr. Stong for your edification. While it is true that most of the angst comes from the locals, uninformed gringos are also stirring the bucked which is ill advised given their prohibition of meddling with affairs of the government at risk of deportation. GDL is more influential than Chapala and will protect their water interests bu seeing the dams keep the lake at a proper level.
Re: [Chapala Payaso] Acueducto -- Si o no?
Can't Post | Private Reply
The Myths of Lake Chapala
The water is dirty – Like unto a shallow lake in the Southeastern USA, where the bottom consists more of silt and clay, rather than sand and rock, the constant actions of the waves on the shores of Lake Chapala keep the minute soil particles in suspension for up to 50-100 meters from the edge. Once into the lake 300 feet, where the water depth may be 3-4 meters, the clarity of the water is much improved.
The water is unsafe for swimming – The international standard for full-body recreational water safety relates to the measurement of coliform bacteria. Given a standard of 200 in the USA and 240 in Mexico for fecal coliform bacteria in a 100 ml water sample it has been shown by three years of testing at 20 sites about the lake that the level is typically 50-60. By contrast note that a fourth of California beaches are closed each day due to bacteria levels above the limit.
The fish from the lake are not safe to eat – Tilapia, catfish and carp are the most common fish in the lake. Of these the carp due to their bottom feeding nature, ingesting suspended sediments, are the most likely to accumulate undesirable substances like heavy metals. Up to the 1990s when more sediments were entering the lake and in 2002 when the lake was only 20% full a condition did exist where in both the water and the fish potentially had some materials which were beyond the limits. For the past six years with the lake level quite high and with over 200 treatment plants along the 700km long river that feeds the lake the lake water is quite good and in turn the fish have no known accumulations of undesired substances. In the winter of 2010 a very large and wide spread testing program of the carp fish for mercury was conducted. With a confidence level well over 90% it has been shown that the level of mercury is at about 0.39 versus a limit of 1.00 parts per million (ppm). Thus, it is similar to what may be found in a can of American tuna fish. Subsequent to these tests similar measurements have been made for lead, arsenic, cadmium and chromium. All were found to be similarly low in both the water and the fish. Since no water has flowed out of this lake in over 30 the key to good water and fish is keeping the lake 60% or more full. This is a condition experienced these past six years and expected to be so for the future since that is essential for the water supply from this lake to the 4 million people in the nearby city of Guadalajara.
The waste water plants about the lake do not work – Waste water treatment across Mexico on averages only 20-30%. By contrast such water treatment in the Lerma River basin that feeds the lake is over 60%. About the lake itself over 85% of all wastewater is treated, thus making this area among the highest in all of Mexico. In sum there are over 200 waste water plants along the Lerma River as well as 16 such plants about the lake. The very low levels of coliform bacteria noted above are indicative of the success in the past 30 years of assuring the lake water is clean and safe. Indeed there are waste water plants that from time to time fail, perhaps 2-4%, which can impact the water out to a distance of 1 km. As a safeguard to temporary outages like this a program of building wetlands in front of such plants is being considered.
The water entering the lake from the Lerma River is highly polluted - Based on materials found deep in the lake sediments it appears that 30 or more years ago that significant amounts of pollutants such as heavy metals were being transported by the Lerma River. In the intervening years the government has built over 200 waste water plants on this 700km long river. The upper third of the river is subject to industrial pollutants (e.g. heavy metals). The middle third receives agricultural pollutants (e.g. fertilizer, pesticides). The lower third of the river than comes to the lake is one of very low water velocity. The end result today is that the treatment plants, while not perfect, appear to accomplish quite a bit on the upper and middle thirds of the river while the forces of nature do a marvelous service on the lower third. The river’s slow passage in this lower third permits not only significant sedimentation of soil to which most potential inorganic pollutants are related but also allows the time required for natural bacteria to act on organics in the water to convert them into CO2 gas that goes into the atmosphere. Contrary to the easy assumption that pollution accumulates as the river flows, it is found that the best of the water in this river is that which enters the lake. In sum, nature, with the aid of government treatment plants in the last 15-20 years has been doing much to overcome pollutants that enter this river The government is presently entering stage three of its plans to treat the water of the Lerma River before it reaches Lake Chapala.
The lake’s level depends on how much it rains in Mexico - From before the time of the Romans until about 1980 the level of the lake depended on the rains sent by God. With the construction of over 200 dams along the Lerma River it became possible by 1980 for man to control the river, the source of 80-85% of the lake’s incoming water. From 1980 to 2002 it appears that the priority of allocation of Lerma River water went to the 1000s of farmers along this river. By 2001 the waters coming into the lake from the river had been so reduced that the lake’s volume was down to about 20%. Because of the needs of Guadalajara with a population of 4 million for water that they would be able to purify by conventional means, and to a lesser degree the desires of the 300,000 people that live about the lake, the federal government orchestrated an agreement with the 5 states through which the Lerma River flows. The compromise while yet allocating up to 80% of the river’s water to the farmers did provide for keeping the lake near to 60% full if at all possible given the rain water collected by the dams in the Lerma River basin. As seen by the last 6 years record of the near constant surface area of the lake, since 2004 the lake has been maintained over 60% full, with periods each year where it reaches to 80% full. Clearly, since 2004 the federal government has shifted the priority of water from the Lerma River farmers to keeping the lake much fuller. This transfer of water from farmers to cities has been the trend all over the world.
Guadalajara as it grows poses a threat of taking all the water from the lake - Presently, during the 8 months of the dry season each year Guadalajara pumps about 18 cm (7.1”) from off the top of the lake. As part of a long past agreement by the federal government the city is now seeking to obtain an additional 6 cm (2.4”) off the top of the lake for its 4 million population. The sum of water used from the lake by the city would then be 24 cm (9.5”). By comparison the lake with an average depth of 600 cm, 6 meters (19.7 ft) see each dry season the evaporation of about 120 cm of water, about 5 times as much water as may in the future be used my Guadalajara. While there is no debate that nothing can be done about evaporation from the lake there is reason to examine where Lerma River water is currently being wasted. The water entering the lake is about 85% from the Lerma River and 15% from runoff from surrounding mountains. In general it seems about 12% of the flow of the river is allocated to cities. Such cities, to include Guadalajara along with its pipeline from the lake, may have as much as 30% water loss due to leaks. That is 4.2% of the water from the Lerma may be lost each year due to pipe leaks in cities. Often not discussed by those close to the lake is the fact that the farmers along the Lerma River receive about 80% of the river’s water. They, due to very inefficient irrigation practices seem to be losing 50% of the water they take. That is 50% of the 80% they receive, thus 40% of the water of the river, is lost by them. Clearly the losses of water from the river by the farmers are 10 times the losses by the cities. Nevertheless, the cities must act to reduce their pipe leaks and the farmers must adopt more efficient irrigation practices. With the current agreement for allocating water between the lake and the farmers along the Lerma River, observed to be working well these past 6 years, each liter of water removed from the lake by evaporation or the use of Guadalajara is being replaced by a liter from the Lerma by controlling the gates on the 200 dams along that river. Given this priority to the lake and in turn Guadalajara’s need it can be seen that famers more and more will be encouraged to move to better irrigation methods.
The Santiago River flows into Lake Chapala – As with many 10 year old Internet sites that cite data of 20-30 years ago about the pollution of the lake, there is confusion over the Santiago River that once drained Lake Chapala. Millions of years ago the lake was as much as 600 feet higher than today. In the past 10,000 years or so the lake level has been near 1510 meters (4950 ft). Beginning about 1850 some dams were developed along the Santiago River to the north of the lake. These dams developed to aid in the irrigation of farm land along the Santiago River on its way from the lake to Guadalajara resulted in the lake level increasing to about 1520 meters (4985 ft). About 1908 a levee was build across the lake near to the city of Jamay in the NE corner of the present lake. This reduced the lake’s area by about a third. Until 1978,with the exception of long lasting periods of drought, water flowed out of the lake into the Santiago River. In turn the Zula River, just to the north of where the Santiago River exits, the lake would at times flow into the lake. However, by 1978 the dams along the Lerma River were capturing more and more of the river’s water to the point that since that year no water has flowed out of the lake. In turn the flow of the Zulu River has been totally into the Santiago River.
The Canadian Pelicans are Ailing Because of Lake Chapala – In recent years evidence of some malformed pelicans and the note of some thin shelled pelican eggs has prompted interest in potential environmental challenges at the lake, at lease near the town of Petetan where the migrating pelicans mass each year. A few years ago a PhD dissertation by Armando Avelar of the University of Guadalajara sought to relate pesticides to these possible ills of the pelicans. That study concluded that the pesticide levels in the lake were low and were not the reason for the pelican ills. It was then conjectured that it might be heavy metals in the lake waters that was the culprit. In the past year the large scale studies by the author for mercury in the water and the fish concluded the levels were low in both cases. Subsequently, less extensive but credible studies of lead, arsenic, chromium and cadmium in the fish and the water have concluded these are also at a low level as long as the lake remains 60% or more full. What might be happening to the pelicans? Visitors to Petetan are each day enthused by the feeding frenzy of the massed pelicans as tons of fish waste are dumped into the lake at this site. Consider that while the flesh of fish has been found to contain low levels of heavy metals that the organs of the fish, now fed in massive amounts to these birds, may contain 10 t0 30 times the level of heavy metals. The design purpose of organs like the liver and kidney is to remove pollutants. For example while the level of mercury in fish may be 0.4 parts per million(ppm) versus a limit of 1.00 the level of mercury could be as high as 12 ppm in these organs that make up a major portion of the diet of these birds who now look to man to feed them.
The Government will never reclaim/relinquish federal zones – In Mexico all waterways, lakes, rivers and even arroyos (10 meters from the centerline) are under the jurisdiction of the federal government. In the case of Lake Chapala the federal jurisdiction extends up to the max level of the lake, Cota 97.8 meters, about 1524 m above sea level, plus 10 meter onto the land beyond that maximum lake water edge. Prior to 1978, when the lake ceased to be full, the width of the exposed lake shore varied as the lake went up and down. In those times people secured “concessions” for a fee to make use of the exposed lake shore, especially for farming. In that the lake has not been full in the past 33 years and may never be full again in the next 100 years due to the claim on the water of the Lerma River by farmers, there is interest in what may be the best public use of the exposed lake shore. At this time it is estimated that the width of the exposed lake shore is on average 80 meters. About the lake this may suggest that there are up to 1400 hectares of exposed shore line that may never again be under the lake’s water. Frequent questions include (1) Will the government remove abandoned fence posts and barbed wire from past concession along the lake edges and extending into the lake up to 200 meters? (2)Will the government stop the illegal building of homes and businesses into this exposed lake bed, estimated to now claim up to 5% of the lake shore? (3) Will the federal government relinquish control of up to 10% of the permanently exposed lake shore areas to the municipios about the lake for appropriate public purposes (e.g. athletic fields, schools, libraries, beaches, and parking for villages whose 400 year old design of streets cannot accommodate? (4) Will the federal government relinquish 1% control of the exposed lakebed to the states to create engineered wetlands in this zone in front of existing waste water treatment plants so as to protect the lake from such plant’s periodic malfunctioning and the ever present challenge of over loading due to growing populations? (5) Will the government remove squatters that move into this zone and thus destroy the value of homes legally built along the shore?
Nothing More Can be Done To Make Mexico’s Largest Lake Better
Wider publication of government testing – Public access to government testing appears limited or at least unknown. Efforts by academic and private parties to provide test data to the public on the water and fish in the lake vary much in quality and quantity. The result is the public via an anxious media in most cases believes the worst as to quality of the water for full body recreation and the eating of fish, both of which are good.
Public efforts to clean up trash that may be seen at the lakes edge – While some government resources may be utilized to clean up highly visible areas, it is imperative due to the 220 km length of the lake shore that the public become involved, even it if it is for 10-20% of the shore. The government might provide trash containers, pay for plastic reclaimed, assign areas to public groups for weekly care and issue awards for cleanliness.
Correction/upgrade of select wastewater plants – It is estimated that up to 4 of the 16 plants about the lake do not function much of the year due to their collector sewer registers being below the level of the lake. In turn the other plants appear on average to be malfunctioning about 2-5% of the time due equipment failures, insufficient operator training, and lack of chorine to disinfect the effluent.
Remove abandoned fence post and barbed wire now in the lake - Masses of currently unemployed fishermen who know best where these obstacles exists maybe paid by the government to remove these hazards to use of the lake.
Dr. Todd D. Stong
Licensed Professional Engineer (USA)
Volunteer Engineer to Local Governments