San Miguel FAQ

Glenn Wilson

We were all surprised by the unusual nocturnal storm, with its gales and great fall of water and hail. The next day we learned about the multiple damages it caused in the urban area of San Miguel. We could view photos and videos of raging streams running through downtown streets and accumulations of mud and stones dragged by the water. These alluvial flows were particularly intense in two streams northeast of the city: the Atascadero stream (Santo Domingo), and the small contiguous Saramago stream, which flows into the Obraje reservoir. Why was such havoc caused by a rain that lasted just over an hour? The answer is not complicated.

Until a few years ago, the high areas located northeast of the city were not as extensively urbanized as they are now. The earth and its plant cover had the ability to absorb the intense rains, reducing the runoff to the streams towards the lower parts of the city. But from the beginning of this century, when the intensive urbanization of these high areas was authorized, these hydraulic dynamics changed radically. More and more the surfaces are occupied by housing developments, shopping centers, industries, etc. These diverse constructions, covered with cement, prevent the penetration of the rainwater into the land. With hundreds of hectares practically sealed, unable to be absorbed, the rainwater drains in large volumes into the natural streams and is carried in the direction of the urban area.

Continue reading The Great Storm of the End of June by César Arias de la Canal in Lokkal.

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Glenn Wilson

I just found this article on Facebook about the same storm and its effects:

San Miguel forms part of the Sub Cuenca Támbula Picachos watershed. Starting in the Picachos mountains, runoff flows right through the center of town via the arroyo Atascadero into the Presa Allende. In the past, even in the heaviest of storms, property was rarely damaged as much of the water was absorbed; the Atascadero and the land above it acting as a natural sponge and buffer zone. However, recently we have been covering that land with cement and stone for new developments, housing and industrial parks. The water that would have been absorbed, hundreds of cubic meters, now flows right into town.

This effect was first noticed when the Luciérnaga Mall was built about a decade ago. After cementing over approximately 100,000 square meters to build the mall, estimates of the increased water flow through the Atascadero Arroyo were as high as 73%. Since then, the municipality has continued to authorize new development in the area. We do not have recent studies, but there is no doubt that the flow of water has only increased as a result of this building, almost certainly setting us up for even more serious flooding that could threaten both property and lives. It also threatens the very developments that are causing the problem. The increased water can potentially wash out the soil underneath, a scenario which has caused building collapse at sites all over the world, such as in Santa Fe, CDMX. It is in everyone’s interests to resolve the situation.

Observatorio Ciudadano de San Miguel de Allende The Greatest danger to our Watershed? Poor City Planning. (Spanish and English; scroll down for English.) More #ObservatorioCiudadano.

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