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Summer 2004
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The Rio Laja Watershed, Guanajuato, Mexico, Improving With GIS

By Dr. Roger F. Tomlinson, Tomlinson Associates Ltd.

  click to enlarge
GPS site locations at the Laja Watershed project.

By any standard, there is a world class watershed rehabilitation effort underway in the Rio Laja Watershed in the state of Guanajuato in the arid center of Mexico. The project is important not only for the backbreaking and effective work that has been accomplished but also for the fact that in 2002 and 2003 more than 700 rural people—from a total of 51 villages, working through six volunteer agencies coordinated and funded by Save the Laja (Salvemos al Rio Laja A.C.) from San Miguel de Allende—established this continuing and expanding program on minimal funding and extraordinary community coordination and cooperation. The role of this project in educating and motivating people cannot be overstated. Men, women, and even young schoolchildren helped with the work.

The Laja Watershed is the largest in the state (1,250,000 acres). Compared to other watersheds in Mexico it is in fair condition. It has minimal industrial pollution. However, the area is arid and becoming increasingly desertified. The watershed is of considerable historical and cultural significance because it is the cradle of Mexican independence. On the banks of the Rio Laja, the colonial cities of Dolores Hidalgo and San Miguel de Allende are regarded as national monuments. Historical and archaeological sites in the region are extensive. Nevertheless, the state of Guanajuato is one of the poorest in the republic and one in which the fertility rate and population are higher than in most areas of Mexico. The per capita rate of migration to the United States is one of the highest in Mexico, in large part because of a deteriorated environment.

The need for rehabilitation is simple to understand. The only water recharging the water supply in the whole area enters into the watershed typically from the upland areas. The upland streams are also historically a major source of water for rural residents. When the summer monsoon-like rains fall, excessively quick runoff occurs because of overforesting, excessive grazing, and poor upland agricultural practices. The water is lost; it doesn't have time to sink in. Soil erosion is high. Small farm production is increasingly devastated. Worse, the remaining soil is degraded, reducing its ability to hold water. Nutrients needed for plant and animal life are leached out, the variety of plants and animals that can exist declines, and the whole ecosystem is threatened. This desertification is the big enemy in the Laja Watershed. In the absence of soil, rural residents must move to cities. This process can be slowed, and even stopped, but it takes time and work.

  photo of the watershed
A detail of the watershed.

That work is being done now in the Rio Laja Watershed. Thousands of small dams are being built to stop the erosion and return the streams to the stable state of a ripple pond. When that has been even partially achieved, trees and other forms of vegetation can be planted, fences put in place to protect the vegetation and river banks from overgrazing, and larger ponds dug for cattle. Good gravel extraction methods are required for downstream rivers, and farmers are using contour plowing and terracing to slow the overall movement of water and soil.

The voluntary agencies active in this work in the 2002–2004 field seasons are

  • Centro para los Adolescentes de San Miguel de Allende (CASA)
  • Cuerpos de Conservación de Guanajuato (CCG)
  • Fundación de Apoyo Infantil Guanajuato (FAI)
  • Grupo Interdisciplinario de Professionistas en Servicios Agropecuarios (GIPSA)
  • Peña Alta A.C. (PA)
  • Grupo Desarollo Rural de Sierra Gorda (SG)

Training in methods of watershed rehabilitation has been provided by the U.S. Forest Service. In 2003, fieldwork coordinators from each of the volunteer agencies underwent two weeks of classroom and in-the-field training in Arizona, followed by instruction in the watershed by U.S. Forest Service staff. GIS training was provided by Esri headquarters staff in Redlands, California, for the senior fieldwork coordinator of Salvemos al Rio Laja.

Note again that this is the only rehabilitation work happening in the Rio Laja Watershed and that it is all funded and coordinated through the efforts of Salvemos al Rio Laja A.C.

The work actually done in the watershed is verified and recorded in the Laja Information System, which works independently of any of the volunteer agencies involved. The equipment and software used by this system were donated by the manufacturers. Esri in California, Canada, and Mexico provided the GIS software, training, and support. Continuing help has been given by Jack Dangermond of Esri; Alex Miller of Esri Canada Limited; and Carlos Salmán Gonzalez of Sistemas de Información Geográfica, S.A. (SIGSA). ERDAS, Inc., provided the ability to interpret satellite images. Hewlett–Packard donated the computer hardware, and Trimble Navigation gave three advanced GPS units for determining exact locations of work in the field. When one GPS unit became unserviceable, Peter Murtaugh of Trimble immediately arranged for it to be replaced. This level of support tells its own story about the value of the work.

This GIS-based system receives fieldwork reports, GPS locations, and photographs from the volunteer agencies of every site in the watershed where work is done. It is an important record for funding agencies to see exactly how their funds have been used, direct the most effective place for future work, and carry out analysis on the results to see if success is being achieved.

It has been verified that in the 2002 and 2003 field seasons, more than 7,500 structures were built at 958 sites, more than 300 trees were planted, fences were erected at 25 sites, three large ponds were excavated, and 98.75 hectares of contour plowing and terracing were carried out. There is every evidence that these numbers will increase substantially in the 2004 field season and will probably double again in succeeding years. This is an enormous amount of work accomplished by well-coordinated volunteer agencies.

Some measures of success have already been observed in 2004, and five categories of success have been identified (see table below).

Category 1 Work done, but no effect
Category 2 Damage control, erosion reduced, soil loss lessened, reduced water velocity
Category 3 Water retention in the arroyos, erosion halted, some sediment buildup
Category 4 Hydrological regime changed, with vegetation indicators; significant aggregation of material; indicator species growing naturally, including grasses (bufel), scrub willow (hellow jarra, jarra del rio), and sedges (juncis)
Category 5 Recovered/Agriculture resumed
Vegetation patches, multiple desirable vegetation communities:
1. Sedges (bulrushes and grasses)
2. Scrub willow
3. A tiered vegetation structure on riparian willow, cottonwood, and alder
1. Step pools in upland areas
2. Ripple pools, meandering systems in midslope
3. Finer sediments lodging in lower areas

Category 1 (failure) has been hard to count as the villages take ownership of their structures and tend to rebuild those damaged during the rainy season. In some villages this has not been done. The degree of rebuilding needs to be documented better and reported on.

As might be expected, there are hundreds of examples of category 2, a smaller number of categories 3 and 4, and no category 5s yet. A public lecture illustrating the results to date was given in San Miguel de Allende on March 22, 2004. A more systematic examination, making full use of the Laja Information System GIS, is being undertaken by the University of Guelph, Canada, who will have had staff on the ground in the watershed (initially for three months) starting on May 10, 2004. The staff used data provided by the Instituto de Ecologia; state government of Guanajuato; and the federal agencies, SEMARNAT and CNA, with the cooperation of SIGSA and coupled with the verified fieldwork reports now in the system.

The University of Guelph will calculate the actual soil loss occurring over the watershed using the Revised Universal Soil Loss Equation that it developed during five years of previous fieldwork experience in Mexico. It will compare the soil loss with the effectiveness of the rehabilitation processes. This will give a way to measure whether "the right thing in the right place" is being done. In future years, the availability of high-resolution satellite imagery may make possible an assessment of changes that will tell the story of overall water retention.

The legacy of Susan Porter Smith, founder and president of Save the Laja, and her vision of rehabilitation of the Rio Laja Watershed is moving ahead with strength and commitment for the benefit of all in this part of the world.

The work in 2002 and 2003 was done by people from the communities of Alanzo Yanez, Alcocer, Cabras de Begona, Canada de Garcia, Canada de la Virgen, Cerrito de los Hernandez, Charco de la Sierra, Cienega de Potreno, Cruz de la Palmar, Dona Juana, El Canajo, El Colorado, El Rincon (Rincon del Esetano), El Saucillo, El Sauz, El Tablon, Estancia de Canal, Estancia de Zamarrripa, Fajardo de Bocas, Fajardo de Tambula, Guadalupe de Tambula, Guanajuantito, Jalpa, Jerico de Trancas, La Calera, La Campana, La Cienega, Laguna (Escondida), La Laguna, La Tinaja, Lagunillas, Llanos de la Fragua, Los Martinez, Maravillas, Ojo de Agua de Tepextle, Palacio de Abajo (Palacio), Picones, Presa de Manatiales, Presa de San Franco, Puerto del Cerrote, Quinteras, Rancho de Enmedio, Rancho de los Ramirez, Rosa de Castilla, Saltrillo, San Lucas, San Marcos de Abajo, Santa Domingo, Santa Rosa, Sosnabar, and Tequisquiapan.

For more information, visit or contact Dr. Roger Tomlinson, Tomlinson Associates Ltd. (tel.: 613-234-1001, e-mail:

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