Water conditions in the Valley of Mexico Basin

Abstract

With more than 22 million inhabitants, the Basin of the Valley of Mexico is the most populated area in Mexico. Within this region 22% of the gross domestic product is generated. The water needs by its inhabitants reaches a gross volume of 2 142 hm3/year and an additional 641 hm3/year for other uses as agricultural, industrial and other services is required. Of this volume, 62% is withdrawn from aquifers located within the basin, 17% comes from surface water and waste-water, and the remaining 21% is imported from other basins. The basin is currently under high water stress, there is an overexploitation about 639 hm3/year, which is almost 40% of the gross groundwater withdrawal. In addition the population, although moderate still is growing, at a rate of 0.6% per year. Since it is a closed basin, infrastructure to solve floods and sewage problems were built starting in the XVII century and continue until our days. Only 15% (95 hm3/year) of the surface runoff is used, the remaining volume of water (521 hm3/year) discharges into the Tula river basin. The total amount of water used in irrigated agriculture, including wastewater, is 207 hm3/year. This amount of water is used to irrigate approximately 24 000 ha. On the other hand, the wastewater volume at the exit of the basin is 1 260 hm3/year. By means of water balance it was estimated a water deficit of 639 hm3/year. The balance was calculated by successive approximations, in order to obtain the infiltration to the aquifers. The basin is under a huge water stress; therefore it is necessary to implement actions to decrease the water use, it also necessary to improve the water monitoring to be able to evaluate the effectiveness of such actions. The proposed structural actions are to increase aquifers recharge, define systems and recharge zones, to make an efficient use of water and to increase the reuse. Water treatment should be wider implemented and its use should be promoted for gardens and car washing, among others. In order to increase the use of surface water it is necessary to build dams. The most important thing is to reduce the water use in the cities. This will require reconsidering the downstream commitments with the Tula River basin. The empirical methods proposed by the norm NOM-011-Conagua-2015, give very accurate results, at least in this exercise. In addition, the present document shows a methodology to obtain the joint availability of surface and ground water, the analysis is carried out by means of successive approximations to obtain the infiltration coefficients for the water use.