Social and Environmental Impact of Karst Erosion on the Atoyac River, Mexico

Abstract:

In recent years there has been an increase in the formation of sinkholes in natural and urban areas in different parts of the world, which respond to both hydrogeological and anthropogenic factors, representing a social and economic danger as well as an environmental one. Such sinkholes are formed by erosion and vertical movement of the soil surface, and can be natural (presence of calcareous formations highly susceptible to water erosion) or human-induced (extraction of groundwater, mining works or failure of sewage pipes).

Erosion of limestone, also known as karst erosion, is associated with most of the sinkholes in the state of Florida in the United States and the formation of cenotes in the Yucatan Peninsula in Mexico. The most alarming aspect of this type of karstic relief is that it covers vast amounts of the earth's surface, both above and below ground, which, being in continuous contact with water, over the years, wears away until the surface collapses. This can lead to sinkholes under houses, on main roads and at the depth of bodies of water, causing the latter to dry out and affecting the water offer in the area.

For example, the disappearance of the Atoyac River in the Mexican state of Veracruz in March 2016 impacted families in eight nearby municipalities and the region's sugar industries, as water was no longer available to satisfy their basic requirements. On-site studies identified, a few kilometers from the river's source, a 20-meter-wide by 30-meter-long sinkhole in the bed that turned the flow of the river into the subsoil. Later, it was ruled that this was due to the dissolution of the limestone present in this mountainous area.

The supervised classification of Landsat 8 satellite images corresponding to a date before and after this event (as well as the comparison with low water times), identified the area affected by the decrease in the flow of the Atoyac River and the increase in sedimented material on its margins, and by analyzing the flow of water from the hydrometric stations on the river, it was possible to determine the decrease in the expenditure contributed by the river, obtaining as a result approximately a loss of 200 liters of water per second, affecting a total of 10,000 families in the nearby municipalities.