ALTERNATIVE SOURCES OF WATER SUPPLY FOR THE CITY OF GUADALAJARA, MEXICO

Guadalajara, Mexico’s second largest city, has a population of ~5 million people and an annual water consumption of ~210 million m³ (170,000 acre-feet). 35% of this water comes from wells, and 65% from the Rio Grande de Santiago. This river is partly fed by controlled releases from Lake Chapala, so its discharge is affected by extended drought conditions in the 52,500 km² watershed that feeds the lake. The lake level has dropped below that of the gravity outlet on several occasions (1950-1958, 1987-1992, and 1996-2002), with consequent sharp drops in the discharge of the river and, hence, on water supply to the city. New sources of water supply need to be developed to cope with these sudden multi-year shortages. *** The city is underlain by a bedrock aquifer hosted by a graben-fill sequence of ignimbrites, air-fall tuffs, lava flows, and interspersed alluvial layers. Yields in some deep wells are significant, so some of the shortfall can be met by constructing additional wells. Shallow groundwater resources, quite extensive in some cases, are available in the basins of the Región Lagunera (to the E of Guadalajara), Amatitán-Arenal ( to the NW), Tala-Ahualulco (to the W), and Villa Corona-San Martin (to the SW), but in all cases would require construction of pipelines and pumping facilities. *** The Rio Grande de Santiago receives the waters from the Verde, Juchipila, and Bolaños rivers downgradient from the city. All three rivers have good potential for construction of new storage reservoirs, but several factors have to be weighted to choose the best source: (1) The Rio Verde flows very close to the city, so conveyance costs would be minimal; in contrast, water conveyance from the Rios Juchipila or Bolaños would require construction of tens of kilometers of canals or pipelines. (2) The Rio Verde experiences significant upstream withdrawals for agriculture, whereas the watersheds of the Rios Juchipila and Bolaños are less intensively used. (3) The watershed of the Rio Verde is farther inland than the other two, so it receives less precipitation and is susceptible to the same drought conditions that affect Lake Chapala. *** We are in the process of collecting the hydrogeologic and engineering data needed to rank the technical feasibility of developing some of these alternative sources.