The functions of dams and reservoirs
Mexico’s dams and reservoirs serve many valuable functions. The first is as a source of hydroelectric power. The amount of power that can be generated is a function of the amount of water streaming through the generators and its pressure, which is related to the height of the dam. Just over half of hydroelectric power is generated by dams on rivers which start in southern mountain ranges and flow into the southern portion of the Gulf of Mexico. Most of the rest comes from dams on rivers along the Pacific coast from the Balsas basin all the way north to Sonora.
Hydroelectric power has been important since the early part of the twentieth century. Currently about 22% of the electricity generating capacity is from hydroelectric plants. The largest hydroelectric plants are on the Grijalva River in Chiapas. Other rivers providing significant hydropower are the Balsas, Santiago, Fuerte, Papaloapan and Moctezuma.
Virtually all Mexican dams, except those in the rainiest southern areas, provide water for irrigated agriculture. This is particularly true in arid northern Mexico. Mexico ranks sixth in the world with about 63,000 cubic kilometers of irrigated agriculture. It is well behind India (558,000), China (546,000), the USA (224,000), Pakistan (182,000) and Iran (76,500). About 23% of Mexico’s cultivated area is irrigated, compared to 99.9% in Egypt, 82% in Pakistan, 47% in China and only 12% in the USA.
Dams also protect against floods, especially in the drier northern areas which are very susceptible to floods from rare but torrential downpours.
In addition, dams provide a source of water for urban populations, especially in the largest metropolitan areas.
Finally, the reservoirs behind dams throughout Mexico are an important recreational resource.
On the other hand, the construction of dams can also have negative effects, including habitat loss, the need to relocate existing residents away from the reservoir site, adverse changes in river flows downstream of the dam and sediment accumulation behind the dam which reduces the reservoir’s capacity.
Chapter 6 of Geo-Mexico: the geography and dynamics of modern Mexico is about water availability, rivers and aquifers; it includes several maps including one showing the relative sizes of the main reservoirs.