Abstract

ORTIZ ZAMORA, Dalia del Carmen  and  ORTEGA GUERRERO, M. Adrián. Origin and evolution of a new lake in the Chalco plain: implications for land subsidence and flooding hazards to the urban areas of Valle de Chalco (State of Mexico) and Tláhuac (Federal District). Invest. Geog [online]. 2007, n.64, pp.26-42. ISSN 2448-7279.

Groundwater extraction from fourteen wells in the Chalco plain since the 1980's, the Mixquic-Santa Catarina System (MSCS), located at the southeast of Mexico City, is causing one of the more important environmental changes of the landscape within the Basin of Mexico in the last two decades. In the middle of the plain, where the thickness of the lacustrine sediments is the highest (300 m), land subsidence of 40 cm/year has occurred as a result of the transient aquitard response to pumping in the underlying main aquifer. A new lake is developing in this topographic depression due to the accumulation of surface water; the shape of the lake is being controlled by the distribution and geometry of a basalt layer that is present within the lacustrine sequence at 50 m depth, originated at the Sierra Santa Catarina. The New Chalco Lake surface is located 12 m below the original position of ground surface, covering a total extension of 1 000 ha. Based on the controls and magnitude of the regional land subsidence, it is expected that the lake surface will grow about 1 500 ha by the year 2015, increasing the risk of flooding to the urban areas of Valle de Chalco and Tlahuac. To reduce the danger and risk of land subsidence and flooding, there is necessary to analyze the convenience to increase the amount and efficiency of the hydraulic infrastructure in the future against the option relocate particular urban areas, within a radius of 2.5 to 3 km with center in the well P9 of the MSCS. The creation of a Metropolitan Council would permit to define dynamic and integral strategies for territory planning, and in particular for prevention of disasters, and the adequate equilibrium between the planning of proposed conservation areas and the environmental improvement with the reduction or mitigation of risk.

Keywords : Subsidence; flooding of urban areas; new Chalco lake; Valle de Chalco; Tláhuac; Mexico; hazardous map.