For thousands of years the flow of the 750-kilometer-long Lerma River was sufficient to exchange the entire water in Lake Chapala each year or two. The abundant excess of water flowed out of the lake and into the Santiago River where it continued past Guadalajara for its 500-kilometer run to the Pacific Ocean.
The first crisis for water (1948-1958) saw Guadalajara come to the defense of the lake because the city’s entire source of electricity was being endangered by the lack of flow from the lake to operate its three hydroelectric power plants on the Santiago River. These plants required 520 million cubic meters per year (Mm3/year), which would be equivalent to about 22 inches off the lake. Additionally, another nine inches of lake water was being sent down the Santiago for irrigation.
For perspective, today the water delivered to Guadalajara to sustain 2.4 million people is equal to about 8 to 10 inches off the lake.
While reduced rainfall in the Lerma River basin was the major cause of this shortage, the quickly expanding consumption of irrigation water in the basin was clearly a growing challenge. By 1978 the over exploitation of the Lerma River basin by irrigation works – nearly 100 percent more demand than supply – marked the point that sufficient water would no longer be available to maintain a full lake.
As a reaction to the low water level, in 1956 a pumping station was created at the northeast corner of the lake at Ocotlan. The objective of this plant was to pump water out of Lake Chapala to supply the hydroelectric power plants on the Rio Santiago, to supply irrigated farms created along that river and, for the first time, to send water to Guadalajara via the Atequiza canal and the newly constructed Las Pintas Canal. This flow to Guadalajara was in time increased to 284 Mm3/year, equivalent to 12 inches off of Lake Chapala. Unbeknownst to most of the public to this day, water has been pumped out of the lake each year at a rate nearly matching that consumed by Guadalajara today to supply water for irrigation and industry along the Rio Santiago.
In 1991 the initial water pipeline of a planned pair was extended from the lake to the city to supply 60 percent of its population. Guadalajara no longer needed to look to the Atequiza – Las Pintas canal system for water.
The second crisis for water at Lake Chapala (1987-2003), while due in part to lower rainfall during that period, was chiefly the result of the enormous 500-700 percent increase in irrigated lands since 1930 in the Lerma River basin, the construction of over 500 dams and reservoirs which then had a storage capacity sufficient to collect the entire flow of the river, and Mexico City’s extraction of over 300 Mm3/year at the head of the river.
Despite 20 years of meetings and hundreds of pages of water agreements, by 2002 the lake was but 14 percent full. While it might be said that Guadalajara was slow to come to the lake’s defense, it was the political might of the nation’s number two city that finally encouraged the federal government to step in. That action reallocated the waters of the Lerma such that by 2004 the lake was restored to 75 percent full and kept above 60 percent for the next five years. Today the lake is about 42 percent full, having silently slipped backward since 2010.
Will Guadalajara come to the defense of the lake again? How can the struggle between the over exploited Lerma River basin and the ever growing city of Guadalajara be resolved? That dilemma will be addressed in next week’s edition of the Reporter.
Todd Stong is a civil engineer who has shared his expertise on water issues as a volunteer advisor to government agencies and environmental groups over more than a decade.